Glossary

abiotic. Having to do with the chemical, geological, and physical aspects of an entity; i.e., the nonliving components.

absolute decomposition. The amount of detritus consumed by microbial decomposers (e.g., bacteria, fungi) and detritivores (e.g., earthworms).

acid–base reactions. A class of chemical reactions involving the transfer of protons without electrons.

acquisition. Any of various processes of acquiring resources from the environment, such as photosynthesis in leaves and nutrient uptake by roots.

adaptation. The evolution of a population by a process of natural selection in which hereditary variants most favorable to organismal survival and reproduction are accumulated, and less advantageous forms are discarded.

adaptive management. Dynamic resource management that incorporates new information gathered from scientific monitoring to systematically improve management practices.

adaptive radiation. The rapid diversification of an ancestral species into several ecologically different species, associated with adaptive morphological, physiological, and/or behavioral divergence.

adaptive syndrome. The suite of morphological, physiological, and behavioral characters that determine an organism’s ability to survive and reproduce.

aerobe. An organism that requires the presence of atmospheric oxygen to live. Distinguished from ANAEROBE.

aerobic. Relating to or occurring in the presence of oxygen. Distinguished from ANAEROBIC.

age structure. The distribution of various chronological ages in a given population.

agroecosystem. An ecosystem designed and managed by humans to produce agricultural goods.

agroforestry. An agricultural system in which woody perennials are deliberately integrated with crops and/or animals on the same unit of land.

airshed. A region sharing a common flow of air.

albedo. Energy reflected from the land or water surface. Generally, white or light-colored surfaces have high albedo, and dark-colored or rough surfaces have low albedo.

alien. Describing a species that occurs outside its natural range and dispersal potential, especially one that becomes established in an ecosystem and threatens native biological diversity or has other negative ecological and economic impacts.

Allee effect. An inverse relationship between population density and per capita population growth rate. Allee effects can accelerate the decline of a shrinking population. (First described by Warder Clyde Allee.)

allele. One of two or more alternative forms of a gene occupying the same chromosomal locus.

allocation. The partitioning of resources among alternative structures or functions within a plant. The principle of allocation states that resources used for one purpose will be unavailable for other purposes, creating trade-offs that strongly influence plant growth and life cycles.

alternative stable state. A relatively stable ecosystem structure or composition that is different from the stable state which was present before a disturbance.

altruism. Behavior that is detrimental to the individual actor performing it but beneficial to one or more other individuals; costs and benefits are measured in terms of effects on fitness, which can be quantified by lifetime reproductive success. Thus, altruistic.

anaerobe. An organism that can live in an environment in which atmospheric oxygen is absent. Distinguished from AEROBE.

anaerobic. Describing or occurring in the absence of oxygen. Distinguished from AEROBIC.

anoxia. The absence of oxygen. Thus, anoxic.

anthropocentrism. 1. Human-centeredness; the perspective that humans are the central entity of the universe. 2. Specifically, the fact of viewing the natural environment primarily in terms of its direct benefit to humans. Thus, anthropocentric.

anthropogenic. Human-caused; describing a phenomenon or condition of the natural world that results from, or is significantly influenced by, human activity.

anthroponosis. A disease transmitted directly from person to person. Compare ZOONOSIS.

apparent competition. An indirect interaction between prey species in which a given prey species experiences more intense predation because of the presence of the alternative prey, as a result of changes in either predator abundance or predator behavior.

assisted migration. A directed dispersal or translocation of organisms across the landscape.

attenuation. A decline in the number of species represented on islands with distance from a source of colonists.

autotroph. A self-feeder; i.e., an organism that can convert inorganic carbon to organic materials and thus does not need to ingest or absorb other living things. Green plants use light energy to make this conversion. Thus, autotrophic.

balance of nature. A popular term for the concept that different species in an ecosystem will tend to interact with each other in a manner that produces a stable state, with populations remaining relatively constant over an extended time.

basic reproductive number. For microparasites, the average number of new infections that would arise from a single infectious host introduced into a population of susceptible hosts. For macroparasites, the average number of established, reproductively mature offspring produced by a mature parasite throughout its life in a population of uninfected hosts. Usually denoted R₀.

batch culture. A method of cell culture in which strains are grown for a fixed period (e.g., a few days) before being transferred to a fresh medium. Compare CONTINUOUS CULTURE.

Batesian mimicry. See MIMICRY.

benthic. Referring to environments or organisms on the sea floor (the benthos).

bioclimatology. The scientific study of the effects of climatic conditions on living organisms.

biocontrol. See BIOLOGICAL CONTROL.

biodiversity. The genetic, taxonomic, and functional variety of all forms of life on Earth, encompassing the interactions among them and the processes that maintain them.

biodiversity hot spot. See HOT SPOT.

bioenergetics. The processes by which energy flows take place in living systems, or the study of such processes.

biogenic. Having to do with life; produced by or involving living things.

biogeochemistry. The scientific study of the physical, chemical, geological, and biological processes and reactions that govern the cycles of matter and energy in the natural environment.

biogeography. The geography of life; i.e., the scientific study of the way in which living organisms are distributed over the Earth, in terms of space and time.

biological control. A nonchemical pest control strategy involving the purposeful release of natural enemies of a pest (often from the pest’s area of origin), with the goal that the enemy will both suppress the density of the pest species and also persist to suppress future outbreaks of the pest.

biological diversity. See BIODIVERSITY.

biological nitrogen fixation. See NITROGEN FIXATION.

biomass. 1. The total mass of living biological material present in a given ecosystem at a certain time. 2. The totality of organic material that can be employed for use as fuel or for other industrial purposes.

biome. Any of various generalized regional or global community types, such as tundra or tropical forest, that are characterized by dominant plant life forms and prevailing climate.

biomechanics. The application of mathematical and biophysical theory to understand animal movement.

bionomic equilibrium. A term for the balance between fish stock abundance and the fishing fleet that a fishery will evolve to in the absence of regulation.

biosphere. The living world; the total area of the Earth that is able to support life.

biotic. Having to do with or involving living organisms.

biotic impoverishment. The generalized series of transitions that occur in the structure and function of ecosystems under chronic elevated disturbance.

bloom. A population outbreak of microscopic algae (phytoplankton) that remains within a defined part of the water column.

bottom-up. Describing strategies and efforts for conservation and restoration that rely on individual, localized initiatives rather than on large-scale government mandates.

bottom-up control. The regulation of ecosystem structure and function by factors such as nutrient supply and primary production at the base of the food chain, as opposed to “top-down” control by consumers.

boundary. Another term for an ECOTONE.

by-catch. The unintentional catch in a fishery of a species not targeted for capture, or of immature members of a targeted species.

carapace. The hard outer shell surrounding the bodies of small animals such as waterfleas and larger animals such as turtles.

carbon sequestration. The process of removing carbon dioxide from the atmospheric pool and making it less accessible or inaccessible to carbon-cycling processes.

carbon sink. 1. A site or reservoir in the environment that takes up released carbon from some other part of the atmospheric carbon cycle; e.g., oceans or forests. 2. More generally, any process or mechanism that removes carbon dioxide from the atmosphere.

cavitation. Another term for EMBOLISM.

chaos. The property of an attractor in a dynamic system that can be roughly characterized as aperiodic and sensitively dependent on initial conditions, and that can be detected by the presence of a positive Lyapunov exponent. In popular use chaos describes random, unpredictable, and disorderly conditions, but the phenomena given the technical name chaos have an intrinsic feature of determinism and some characteristics of order.

character adaptation. A character that evolved gradually by natural selection for a particular biological role, through which organisms possessing the character have a higher average rate of survival and reproduction than do organisms having contrasting conditions that have occurred in a population’s evolutionary history.

character displacement. The evolution of enhanced differences between two species in the same geographic location, as a result of selection against members of one or both species that use the same resources as members of the other species (i.e., ecological character displacement) or against individuals that tend to hybridize with members of the other species (i.e., reproductive character displacement).

chemoautotrophy. A mode of nutrition by which an organism can reduce inorganic carbon to organic matter in the absence of light, using preformed bond energy contained in other molecules.

chemotroph. An organism that makes its own food but, instead of using energy from the sun as photosynthetic organisms do, uses inorganic chemicals as an energy source.

classical biological control. See BIOLOGICAL CONTROL.

climax community. A stable community of organisms in equilibrium with existing environmental conditions; this represents the final stage of an ecological succession.

cline. A geographic gradient in the frequency or mean value of a phenotype or genotype.

coalescence. The point at which common ancestry for two alleles at a gene occurs in the past.

coancestry. The probability that two alleles sampled from two different individuals are identical by descent.

coefficient of relatedness. The probability that one animal shares an allele carried by another as a result of descent from a common ancestor.

coevolution. A process of reciprocal evolutionary change in two interacting species, driven by natural selection.

coevolutionary cold spot. A geographic region in which one of a set of interacting species does not occur or in which the interaction, although occurring, does not result in reciprocal evolutionary change.

coevolutionary hot spot. A geographic region in which the interaction between two or more interacting species does result in reciprocal evolutionary change.

coexistence. The indefinite persistence of two or more species within the same community; this involves species that will continue to persist in the face of perturbations in their abundances. Species that co-occur may or may not be stably coexisting, because one or more of them may be on the way to local extinction at a time scale that is too slow to be immediately apparent.

coextinction. A process in which the extinction of one species triggers the loss of another species.

colonization. The successful occupation of a new habitat by a species not previously found in this locale.

cometabolism. The simultaneous metabolism of two substrates in such a manner that the metabolism of one substrate occurs only in the presence of the second substrate.

common-pool resource. A resource system in which it is costly to exclude potential beneficiaries, but in which one person’s use subtracts resource units from those available to others.

community. An assemblage of species found together in a specific habitat at a certain time, interacting with each other in this area.

community genetics. The study of the role played by intraspecific genetic variation in community organization or ecosystem dynamics.

community module. A small number of species involved in a clearly defined pattern of interactions, such as two consumers competing for a shared resource, or two prey species interacting indirectly through their impacts on a shared predator.

community organization. A general term for the number of species found in a community, their relative abundances, and their pattern of interconnections by means of competition, exploitation, and mutualism.

competition. Ecological interaction in which two or more species negatively affect one another by consuming common resources or by other harmful means.

complementarity. The fact of two or more species using the same resources in different ways.

complementarity effect. The influence that combinations of species have on ecosystem functioning as a consequence of their interactions (e.g., resource partitioning, facilitation, reduced natural enemy impacts in diverse communities).

complex adaptive system. A system characterized by individuality and diversity of components, localized interactions between those components, and an autonomous process that selects a subset for replication and enhancement from among components, based on the results of local interactions.

conceptual landscape model. A theoretical framework that provides the terminology needed to communicate and analyze how organisms are distributed through space.

connectivity. The linkage of habitat, land cover, or ecological processes from one location to another or throughout an entire landscape.

conservation. An action taken to promote the persistence of biodiversity.

conspecific. An organism of the same species as another or others.

conspecific attraction. The attraction of individuals to members of the same species during the process of habitat selection.

constraint. Any of various factors that can absolutely limit certain actions of an organism.

consumer. An organism that consumes food from other organisms; a HETEROTROPH.

consumer–resource interaction. Any interaction in which one species depends on another for sustenance, including interactions between populations of predators and prey, or parasitoids and hosts.

context dependency. Spatial and temporal variation in the strength and/or outcome of mutualism that can be attributed to the local environmental context.

continental shelf. See SHELF.

continuous culture. A method of cell culture in which there is a continuous input of nutrients and output of spent medium, resulting in constant environmental conditions. Compare BATCH CULTURE.

continuum. A distribution of many species along a gradient, in which each species appears to be distributed randomly with respect to other species.

convergence. The development of increasing similarity over time, usually applied to species somewhat unrelated evolutionarily. Also called convergent evolution.

cooperation. 1. Mutually beneficial interactions among individuals of the same species, often involving social interactions such as foraging or parental care. 2. More generally, any behavior that benefits two or more interacting individuals.

corridor. A relatively linear area connecting two or more habitats, facilitating the movement of organisms between local populations.

critical habitat. The ecosystem on which any target species depends, such as endangered or threatened pollinators.

critical population size. The population size of susceptible hosts for which R₀ = 1, where R₀ is the BASIC REPRODUCTIVE NUMBER, and which must therefore be exceeded if an infection is to spread in a population.

critical transition. A change in the dominating feedback processes in an ecosystem, with implications for ecosystem structure and functioning. Systems undergoing a critical transition may be profoundly different than before the transition.

cropland. An official term for all land used for growing crops, including the sum of arable lands (land under temporary crops or temporarily fallow) and permanent crops (long-growing crops such as cocoa, coffee, rubber, fruit trees, nut trees, and vines).

culturability. The ability to grow strains in a laboratory in pure culture. Thus, culturable.

cultural services. The nonmaterial benefits people obtain from ecosystems through such factors as spiritual enrichment, cognitive development, reflection, recreation, and aesthetic experiences.

dead zone. A portion of the ocean or another body of water with very low levels of dissolved oxygen, forming in areas with low circulation and excess primary production (EUTROPHICATION).

decomposition. The breakdown of organic residues carried out by bacteria and fungi, resulting in the release of energy, nutrients, and carbon dioxide.

deforestation. A large-scale process of clearing land of trees or forest, as for logging, agriculture, housing, or the like.

demersal. Describing an organism that lives on or near the bottom of the ocean or a deep lake, especially one that feeds on benthic (bottom) organisms.

demographic stochasticity. Unpredictability through time in a population’s demography, caused by the randomness of individual fates. This type of stochasticity is usually important only at very small population sizes.

demography. The statistical study of trends in population, including how many individuals die, how many reproduce, how they are distributed by age, their geographic location, and so on.

denitrification. The microbial process that converts nitrate (NO₃^-, a nutrient readily available to plants) to nitrite to free nitrogen gas (N₂, generally unavailable to plants); this requires a carbon source and an anaerobic environment.

density. The relative number of individuals of a given species that are found in a certain area.

density dependence. The fact of the growth rate of a population varying in accordance with the abundance or density of the organism in question, as when the per capita rate of increase of the population decreases as the population’s density increases.

density-dependent. Describing a process that varies in accordance with the population density of the species concerned. For instance, below a certain host population size, parasitic infections may not occur (there are not enough hosts for the parasite to be transmitted between them), whereas above a certain host population size, parasitic infections may become prevalent.

density-dependent transmission. Parasite transmission in which the rate of contact between susceptible hosts and the source of new infections increases with host density; the probability of any individual host getting infected thus depends on the density of surrounding hosts.

desertification. The development of desert conditions in an area that was previously not an arid environment, as a result of climatic changes and/or human activity.

detrital. Having to do with or consisting of detritus (dead primary producer material).

detrital production. The amount of net primary production not consumed by herbivores, which senesces and enters the detrital compartment.

detritivore. An organism that feeds on DETRITUS. Thus, detritivorous.

detritus. Dead or decomposing primary producer material, which normally becomes detached from the primary producer after senescence.

developmental constraint. A bias in the morphological forms that a population can express, caused by the mechanisms and limitations of organismal growth and morphogenesis.

diapause. A physiological condition in which an organism can remain dormant to survive long periods of challenging conditions such as low temperatures or drought.

diauxie. Literally “double growth”; a description of the manner in which bacterial populations feed on mixtures of substrates (usually sugars). Diauxic growth is characterized by an initial growth phase, followed by a lag as the strain switches from the first to the second substrate, which in turn is followed by a second growth phase as the second substrate is utilized.

diet choice. The decisions made by foragers regarding which encountered food items to consume and which to reject. The abundances of different food types, their ease of being found and manipulated, and their value to the forager generally influence the decision to eat or not to eat.

diffuse coevolution. The extension of the coevolution of two populations to multiple other populations in the community.

dilution rate. In cell culture, the rate at which nutrients are input into (and output from) the microcosm.

direct effect. The immediate impact of one species on another’s chance of survival and reproduction, through a physical interaction such as predation or interference.

directional transition. The location of a boundary between two areas that moves in one direction through time.

disaptation. A character that decreases its possessor’s average rate of survival and reproduction relative to contrasting conditions evident in a population’s evolutionary history. A primary disaptation is disadvantageous when it first appears; a secondary disaptation acquires a selective liability not present at its origin as a consequence of environmental change or an altered genetic context.

discharge. Movement of the water in an aquifer back to surface water.

dispersal. The movement of individuals among local populations in a larger population.

disruptive selection. A process of selection that favors opposite extremes of a trait within a single population.

dissolved matter. A term for organic matter derived from the degradation of dead organisms, consisting of molecules that are typically less than 0.7 μm in size. Compare PARTICULATE MATTER.

disturbance. An episodic event that results in a sustained disruption of an ecosystem’s structure and function, generally with effects that last for an extended time. This may be a physical disturbance (e.g., fire, flood, drought, volcanic eruption), a biogenic disturbance (e.g., colonization by herbivorous insects or mammals), or an anthropogenic disturbance (e.g., deforestation, drainage of wetlands, chemical pollution, alien species introduction).

divergent (natural) selection. Selection arising from environmental forces acting differentially on phenotypic traits (morphology, physiology, or behavior) resulting in divergent phenotypes.

diversity. The fact of being varied or different. See BIODIVERSITY.

α, β, γ diversity. The species diversity (or richness) of a local community or habitat (α diversity); the difference in diversity associated with differences in habitat or spatial scale (β diversity); the total diversity of a region or other spatial unit (γ diversity).

diversity index. A mathematical expression that combines species richness and evenness as a measure of diversity.

domain. The range of characteristic scales in time and space at which a particular process operates, such as the delivery of an ecosystem service.

dynamics. The changes through time in the size of a population, or in a related measure such as density.

early successional species. Species that appear in an ecosystem following a disturbance event, such as a fire, landslide, or logging. Early successional species typically possess r-selected traits, such as high dispersal ability, short generation time, and rapid growth, but at the expense of having a short lifespan and poor competitive ability. As a result, their population sizes usually increase immediately after disturbances, and then decline later as conditions become more crowded and they are competitively replaced by LATE SUCCESSIONAL SPECIES.

ecological. 1. Having to do with the natural environment or the science of ecology. 2. Having to do with the protection or sustainable use of the natural environment.

ecological character displacement. Divergence in ecological traits caused by competition for shared resources; this may lead to reproductive isolation as a by-product.

ecological economics. The study of the interactions and coevolution in time and space between ecosystems and human economies.

ecological epidemiology. The study of infectious diseases in the context of the interactions between parasites and hosts.

ecological extinction. A reduction of the distribution and abundance of a species, to the point that it no longer significantly affects the distribution and abundance of other species in the ecosystem.

ecologically based divergent selection. Selection arising from environmental differences and/or ecological interactions (e.g., competition) that acts in contrasting directions on two populations (e.g., large body size confers high survival in one environment and low survival in the other) or favors opposite extremes of a trait within a single population (i.e., disruptive selection).

ecologically sustainable. A descriptive term for a fishery regulated so as to avoid any shift in the ecosystem that leads to an undesirable state, such as collapsed populations of a harvested species.

ecological network. A set of species that are connected to one another via some form of interaction, either trophic (as in a food web) or nontrophic (e.g., pollination, seed dispersal).

ecological niche. See NICHE.

ecological release. The expansion of habitat or use of resources by populations into areas of lower species diversity with reduced interspecific competition.

ecological speciation. A process by which barriers to gene flow evolve between populations as a result of ecologically based divergent natural selection.

ecological stoichiometry. The balance of multiple chemical substances in ecological interactions and processes, or the scientific study of this balance.

ecological succession. See SUCCESSION.

ecological trap. The attraction of animals to habitats where they perform more poorly, even when higher-quality habitat is available.

ecology. The branch of science concerned with the interrelationships of organisms with each other and with their environment.

ecomorph. An organism, population, or species whose physical appearance is determined by its environment.

ecosphere. Another term for BIOSPHERE.

ecosystem. A natural unit consisting of all the plants, animals, and microorganisms (biotic) factors in a given area, interacting with all of the nonliving physical and chemical (abiotic) factors of this environment. An ecosystem can range in scale from an ephemeral pond to the entire globe, but the term most often refers to a landscape-scale system characterized by one or a specified range of community types (e.g., a grassland ecosystem).

ecosystem-based management (EBM). A holistic approach to resource management aimed at the sustainable delivery of multiple ecosystem services by accounting for the ecological, environmental, and socioeconomic context and explicitly addressing cumulative impacts and trade-offs among the different sectors being managed.

ecosystem processes. The biogeochemical flows of energy and matter within and between ecosystems, e.g., primary production and nutrient cycling. Also, ecosystem function(ing).

ecosystem property. A measure of the status (e.g., species richness or standing biomass) or dynamic properties (e.g., resilience, resistance, susceptibility to invasion) of an ecosystem.

ecosystem services. The conditions and processes by which ecosystems and the species that comprise them sustain and fulfill human life. These include critical provisioning services such as food, timber, fiber, fuel and energy, and fresh water; regulating services that affect or modify factors such as air and water quality, climate, erosion, diseases, pests, and natural hazards; cultural services such as fulfilling spiritual, religious, and aesthetic needs; and supporting services such as soil formation, photosynthesis, and nutrient cycling.

ecosystem service trade-off. The reduction of the provision of one ecosystem service as a consequence of increased use of another service, due to management choices made by humans.

ecotone. A transition area where spatial changes in vegetation structure or ecosystem process rates are more rapid than in the adjoining plant communities.

ectotherm. An organism that uses external sources of heat for metabolism and whose rate of metabolism is closely linked to ambient temperatures; e.g., invertebrates, fish, amphibians, or reptiles. Thus, ectothermic.

edge. A well-defined area between patch types; this is often a barrier, constraint, or limit to the movement of animals and plants.

edge effects. Changes in population sizes, species richness, or other aspects of the ecology of individuals, populations, or communities at the interface between two habitat types.

effective population size. An ideal population that incorporates such factors as variation in the sex ratio of breeding individuals, the number of offspring per individual, and numbers of breeding individuals in different generations.

El Niño–Southern Oscillation (ENSO). Sustained sea surface temperature anomalies across the central tropical Pacific that are associated with the spread of warm waters from the Indian Ocean and Western Pacific to the Eastern Pacific and that are a major influence on global climate, especially in the Southern Hemisphere. (From the Spanish term El Niño, meaning “the Christ child,” because the phenomenon was first observed at around Christmas time.)

embolism. In plants, the blockage of water transport by air bubbles in the xylem (water-transporting cells), causing reduced water transport and, potentially, plant death.

emerging (infectious) disease. A disease of infectious origin whose incidence in humans has increased in the recent past or threatens to increase in the near future. It can be a completely new disease or an old disease occurring in new places or new populations, or one that is newly resistant to available treatments.

endangered. Describing a species that is predicted to be in danger of extinction throughout all or a significant portion of its range.

endemic. 1. A species that has a relatively narrow geographic range, such as one that is found only on a particular island or in a particular habitat or region. 2. Having to do with or describing such a species. Thus, endemism.

energetic equivalence. A concept that denotes the equivalence of species in terms of the amount of energy that their populations use within natural communities.

energy budget. A calculation or description of the relative energy flows into and out of a living system, such as a lake or an individual organism.

entropy. A measure of the randomness or disorder of a system, which in a living system will increase over time as its energy content degrades to usable heat. Thus animals must compensate for ever-increasing entropy by constantly acquiring energy via food.

environmental stochasticity. Unpredictable changes through time in the average demographic rates of a population. These changes can be caused by vacillations in weather, food, predation, or other biotic and abiotic forces influencing individuals in a population and can exert strong effects on the dynamics of populations.

environmental uncertainty. Unpredictable sources of density-independent changes in population level parameters.

epilimnion. The uniformly warm upper layer of a lake when it is thermally stratified in summer.

equilibrium. The level of density at which a population will remain, once it has reached this level, if the population is not perturbed.

euphotic zone. The upper portion of the ocean where there is sufficient light to support net photosynthesis, usually the upper 0–200 m in the clearest ocean water.

eutrophic. Describing a lake or other body of water that is richly supplied with plant nutrients and supportive of heavy plant growths.

eutrophication. The overenrichment of an ecosystem resulting from excessive additions of chemical nutrients; eutrophication may create anaerobic conditions (“dead zones”) in aquatic ecosystems.

evapotranspiration. The evaporation of water vapor from surfaces as well as the evaporation of water through the plant and leaf stomata by transpiration.

exaptation. The appropriation of a character through natural selection for a biological role other than the one by which the character was constructed through natural selection.

exclusion. A condition in which a species is driven to local extinction as a consequence of a competitive interaction.

exclusive economic zone (EEZ). The area bordering a nation’s coast where it has special rights over the exploitation and management of natural resources, including fish, minerals, and petroleum. Except in areas of overlap, the EEZ extends 200 nautical miles offshore.

existence value. The worth that humans place on the mere fact of knowing that certain species or ecosystems exist, even though they may not experience or make use of them personally.

exotic. Describing any nonnative species deliberately or accidentally introduced into a new habitat.

exploitation. The use of a natural resource by humans. See also OVEREXPLOITATION.

exploitative competition. A process in which individuals have indirect negative effects on other individuals by acquiring a resource and thus depriving those others of access to the resource.

extensification. The practice of increasing the amount of agricultural land that is under cultivation.

extent of occurrence. The area that falls within the outermost geographic limits of the occurrence of a species.

externality. In ecological economics, a third-party effect of a transaction that is not taken into account by the parties to the transaction. External effects may be positive or negative and can drive a wedge between the private and social net benefits of a transaction.

extinction. 1. The complete disappearance of a species, involving the death of all its members; more precisely termed global extinction. 2. The disappearance of a species from a given habitat or ecosystem, though it still exists elsewhere; more precisely termed local extinction.

extinction debt. A future loss of species that are subject to habitat destruction or fragmentation, but that have not yet reached an EXTINCTION THRESHOLD; these species are predicted to become extinct over time though this has not yet occurred.

extinction threshold. The point at which a species’ meta-population begins a critical decline, as from habitat loss and fragmentation, so that recolonizations will not be sufficient to compensate for local extinctions, and the entire metapopulation will become extinct even if some habitat patches exist in the landscape.

extinction vortex. As populations decline, an insidious mutual reinforcement occurring among biotic and abiotic processes to drive population size downward to extinction.

extirpation. The process by which a species is rendered extinct in a particular area or country while it survives in others. When a species consists of several populations, the extirpation of the last population is equivalent to the global extinction of that species.

facilitation. The positive effect of one species on another.

facultative mutualism. A type of mutualism that increases an organism’s success but that is not absolutely required for its survival and/or reproduction.

fecundity. The innate capacity to produce offspring.

fertility. 1. The fact of producing offspring. 2. The ability of soil to support plant life, especially agricultural plants. Thus, fertile.

fertility rate. The number of offspring produced by a female over a lifetime or during a specific age interval.

fire regime. The historic pattern of fires in a given ecosystem, in terms of frequency, severity, and extent.

fire return interval. The number of years between two successive fire events at a particular location.

fire suppression. An intentional effort to prevent wildfires in a forest ecosystem.

fishery. 1. A site for harvesting or catching fish or other aquatic life. 2. The sum of activities involved in the obtaining of fish or other aquatic life.

fishing down (through) the food web. The process by which the fisheries within a given marine ecosystem, having depleted the preferred large predatory fish at the top of the food web, turn to increasingly smaller species, finally ending up with previously spurned small fish and invertebrates.

fish stock. A population of a single species that is geographically distinct enough to be managed separately from other populations of the same species.

fitness. The extent to which an individual contributes its genes to future generations relative to other individuals in the same population; i.e., the individual’s relative reproductive success.

food chain. A description of an ecological system in terms of the feeding linkages and energy and materials flows among major groups of species therein (plants, herbivores, decomposers, carnivores).

food web. A network of feeding relationships among organisms in a local community.

food web compartment or channel. A subweb; i.e., a frequently and strongly connected set of species that connect with much lower frequency and strength to other species in the larger web.

food web connectance. The number of actual links or interactions in a food web divided by the maximum possible links.

food web pathway. A directed set of interactions from any one species to another (e.g., a resource to a consumer to a predator of the consumer).

foraging games. The behavioral challenges facing both predator and prey when the prey can perceive and respond to the hunting tactics of the predator and the predator can perceive and respond to the antipredator tactics of its prey.

forest fragmentation. The disruption of extensive forest habitats into isolated, smaller patches.

forest management. An approach to maintaining or restoring the composition, structure, and function of natural and modified forests, based on a collaborative vision that integrates ecological, socioeconomic, and institutional perspectives, applied within naturally defined ecological boundaries.

founder control. A condition in which the dominant species in a competitive interaction is the species that is initially most abundant.

founder event. The establishment of a new population with few individuals that contain a small, and hence unrepresentative, portion of the genetic diversity relative to the original population, potentially leading to speciation.

frequency-dependent transmission. Parasite transmission in which the rate of contact between susceptible hosts and the source of new infections is independent of host density.

F_ST. A measure of genetic differentiation among populations, expressing the proportion of variance within a set of local populations that results from the differentiation among them.

function. The use, action, or mechanical role of phenotypic features.

functional diversity. The variety and number of species that fulfill different functional roles in a community or ecosystem.

functional group. A group of species that share a common ecological function, regardless of their taxonomic affinities; e.g., the diverse assemblage of herbivores found on coral reefs.

functional response. The relationship between per capita resource consumption and resource abundance.

Gaia hypothesis. A description of the entire Earth as a unified superorganism. (Named for the ancient Greek goddess of the Earth.)

gap dynamics. A form of natural disturbance in certain forest types, in which an opening (gap) in the overstory alters the competitive environment, thus favoring the establishment or regeneration of certain species in the understory.

gene flow. Movement between groups that results in genetic exchange.

genetic bottleneck. A period during which only a few individuals survive and become the only ancestors of the future generations of the population.

genetic drift. Chance changes in allele frequencies that result from small population size.

genetic load. A decrease in average population fitness (relative to the fittest genotype) caused, for example, by immigration of locally less-adapted immigrants (migration load), mating among relatives (inbreeding load), fixation of deleterious alleles (drift load), or any other population process.

genetic stochasticity. Unpredictable changes in gene frequencies as a result of processes such as random genetic drift. This is usually important only at very small population sizes.

genome. The complete assembly of genes present in a given organism, coded by specific nucleotide sequences of DNA, that determines its taxonomic structure, metabolic characteristics, behavior, and ecological function.

geographic population. All the viable populations of a species found within the species’ geographic range.

geographic range. The spatial region that includes all the viable populations of a species.

geomorphology. The study of the formation, alteration, and configuration of landforms and their relationship with underlying structures.

geophagy. The eating of dirt. This behavior may be used to balance mineral intake for animals living in environments of low food quality.

geospatial. Having to do with the distribution of information in a geographic sense in such a way that entities can be located by some coordinate of a reference system (e.g., latitude and longitude), which places these entities at some point on the globe.

global carbon balance. The long-term net flux of carbon between terrestrial and marine ecosystems and the atmosphere.

global extinction. See EXTINCTION.

global positioning system (GPS). A set of 24 satellites that orbit the Earth and communicate their position to a ground receiving device in order to determine the geographic location of that receiver.

gonotrophic cycle. The complete cycle of time between a mosquito’s blood feeding and subsequent laying of eggs.

gradient. A transitional geographic area in which environmental conditions vary.

gradualism. The accumulation of individually small quantitative changes in a population leading to qualitative change. Compare SALTATION.

grasslands. Short-stature vegetation dominated by grasses; characteristic of locations with a strong water limitation for at least part of the year.

greenhouse gases (GHGs). Gases such as carbon dioxide, methane, nitrous oxide, tropospheric ozone, or chlorofluorocarbons that absorb solar radiation and reflect it back down to Earth, creating a “greenhouse effect” that warms the Earth’s surface.

gross primary production. The amount or rate of organic matter (sugars) produced from carbon dioxide by green plants through photosynthesis.

group selection. The concept that behaviors detrimental to an individual can evolve because they benefit the larger group of which it is a member.

growth rate hypothesis. The principle that differences in organismal C:N:P (carbon–nitrogen–phosphorus) ratios are caused by differential allocations to RNA necessary to meet the protein synthesis demands of rapid biomass growth and development.

guild. A group of species that exploit the same class of environmental resources in a similar way.

gyre. A major cyclonic surface current system in the ocean, roughly corresponding to the unproductive, highly stratified areas of the oceans that are most remote from the continents.

habitat. The place where an organism or population lives.

habitat fragmentation. The spatial isolation of small habitat areas that compounds the effects of habitat loss on populations and biodiversity.

habitat selection. The process by which individuals choose areas in which they will conduct specific activities.

HANPP. A measure of how much of the biological productivity of a given location is used, consumed, or co-opted by human activities. (An acronym for human appropriation of net primary production.)

Hardy-Weinberg principle. The concept that after one generation of random mating, single-locus genotype frequencies can be represented as a binomial function of the allele frequencies. (Named for G. H. Hardy and Wilhelm Weinberg.)

herbivore. An animal that feeds solely on plant tissue. Thus, herbivorous.

herbivory. The consumption of living plant material.

herd immunity. A condition in which a population contains too few susceptible hosts (either because of natural infection or immunization) for infection to be able to establish and spread within the population.

heritability. 1. The fraction of the total phenotypic variation in a population that can be attributed to genetic differences among individuals. 2. More specifically, that fraction of the total phenotypic variation that results from the additive effects of genes.

heterosis. An increase in fitness resulting from matings among individuals from different populations (e.g., as a result of superdominance or drift-load effects).

heterospecific attraction. The attraction of individuals to other potentially competing species during the process of habitat selection.

heterotroph. An organism that must consume organic compounds as food for growth (e.g., animals, most bacteria, and fungi). Thus, heterotrophic.

heterotrophic respiration. The metabolic process by which consumers (heterotrophs) convert sugars to carbon dioxide, releasing energy.

heterozygosity. The proportion of individuals in a population that have two different alleles for a particular gene.

holistic community. The concept that species within a community are highly interdependent, forming organismlike units.

homeostasis. The fact of an organism, or a system, maintaining constant internal conditions in the face of externally imposed variation.

hormone. Any of various substances acting as chemical messengers to carry information from one part of an organism (e.g., the brain) to another (e.g., the gonads), often via the blood transport system. Hormones bind to receptors on target cells and thus regulate the function of their targets. Various factors influence the effects of a hormone, including its pattern of secretion, transport processes, the response of the receiving tissue, and the speed with which the hormone is degraded.

host. The organism from which a parasite obtains its nutrition or shelter.

host plant. The plant on which an insect herbivore feeds.

hot spots. Regions with exceptionally high species richness, termed “hot” because they are often selected as priority targets for efforts to protect and conserve ecosystems.

human appropriation of net primary production. See HANPP.

Hutchinsonian ratio. The body size ratio of larger species over smaller species in a pair of species; niche theory predicts that co-occurring species should have larger body size ratio than expected by chance. (Developed by G. Evelyn Hutchinson.)

hydraulic lift. The process by which some plant species passively move water from deep in the soil profile, where water potentials are high, to more shallow regions where water potentials are low.

hydrology. The study of the properties, distribution, and effects of water on the Earth’s surface.

hypolimnion. The uniformly cool and deep layer of a lake when it is thermally stratified in summer.

hyporheic zone. The subsurface region under and lateral to a stream in which groundwater and surface water mix; considered metabolically important in streams and rivers.

hypoxia. A low level of atmospheric oxygen. Thus, hypoxic.

hysteresis. The phenomenon that the forward shift and the backward shift between alternative attractors happen at different values of an external control variable.

inbreeding depression. The decline in measures of individual performance (e.g., survival, growth, or reproduction) sometimes observed in offspring of parents that are closely related to one another.

indirect cues. Stimuli produced by factors that are correlated with other factors with direct effects on intrinsic habitat quality.

indirect effect. The impact of one species on another’s chance of survival and reproduction mediated through direct interactions with a mutual third-party species.

indirect interaction. An interaction between two species that is modified by a third species.

individualistic communities. The principle that communities are in essence groups of populations that occur together mainly because they share adaptations to the same abiotic environment; i.e., communities do not have organism-like qualities.

instability. The fact of being unstable. See STABILITY.

insular biogeography. See ISLAND BIOGEOGRAPHY.

intensification. A term for the practice of stimulating more agricultural production per unit area, mainly through increasing use of agricultural chemicals, irrigation water, high-yielding plant varieties, and machinery.

interaction strength (IS). The dynamic influence of one species on another, either direct or indirect.

interference competition. Competition in which individuals have direct negative effects on other individuals by preventing access to a resource through aggressive behaviors such as territoriality, larval competition, overgrowth, or undercutting.

interspecific. Having to do with or involving individuals of different species.

intraguild predation. A predation event in which one member of the feeding guild preys on another member of the same guild (predators consuming predators).

intraspecific. Having to do with or involving individuals of the same species.

intrinsic habitat quality. The expected fitness of an individual when it lives in or uses a given habitat, after controlling for any effects of conspecifics on fitness.

intrinsic rate of increase. The maximum per capita population growth rate for a population with a stable age structure (i.e., the proportions of the population in different age groups remain the same). The intrinsic rate of increase is often achieved when the population is at low density.

intrinsic value. A term for the value that other species have independent of their value to humans.

introduced species. A species established by human action in an area outside its natural range.

introduction. The movement, by human agency, of a species, subspecies, or lower taxon (including any part, gamete, or propagule that might survive and subsequently reproduce) into an area outside its natural range (past or present).

invasion. The fact of a nonnative species becoming established in a novel location, often with negative ecological consequences.

invasive species. A nonnative species that has become established in a new area outside its natural range. Also, invader.

inversion layer. The cap of the planetary boundary layer, where there is little or no vertical mixing and where the temperature may increase or remain constant.

irreplaceability. The status of a given site whose protection will be required for a system of conservation areas to meet all targets or to otherwise optimize a conservation objective function.

island biogeography. A branch of biogeography that studies the factors that affect the number of different species on a given island; “island” in this context can refer not only to the literal sense of a body of land surrounded by water, but also by extension to any isolated ecosystem surrounded by unlike ecosystems. The theory of island biogeography (Robert H. MacArthur and Edward O. Wilson) proposes that the number of species in a given island results from the dynamic equilibrium of the opposite processes of immigration from a source and local extinctions.

isotopic record of carbon. The changes in the ratio of carbon-13 to carbon-12 over geological time in marine carbonates or in organic matter in sediments or sedimentary rocks.

iteroparous. Describing a reproductive pattern in which individuals reproduce more than once in their lives. Thus, iteroparity.

IUU. An acronym for illegal, unreported, and unregulated fishing.

juvenile. A preadult stage in the development of an organism, resembling the adult but not yet reproductively mature.

keystone predator. A predator that strongly interacts with its prey and facilitates their coexistence; its removal from an ecosystem would significantly impact community organization.

keystone species. A species that has a disproportionately large impact on ecosystem structure and function relative to its own abundance.

kinematics. 1. Animal movement; the angles, velocities, and rates at which different body parts move throughout space. 2. The scientific study of such processes.

kin selection. Selection resulting from the effects of an organism on the fitness of its relatives, as well as through the organism’s own reproduction.

kinetics. 1. The forces produced by organisms during dynamic movements. 2. The scientific study of such movements. Thus, kinetic.

lake turnover. The mixing of deep anoxic (oxygen-poor) and shallow oxygen-rich water in lakes, occurring in fall and spring when water reaches the threshold temperature of 4°C.

land cover. The physical state of a land area in terms of its surface features, such as “rainforest,” “cropland,” or “desert.”

landscape. A human-defined area of the natural terrestrial world, typically ranging in size from about 1 km² to about 1000 km².

landscape connectivity. The ability of a landscape to facilitate the flows of organisms, energy, or material across a patch mosaic; this is a function of both the structural connectedness of the landscape and the movement characteristics of the species or process under consideration.

landscape dynamics. The manner in which a landscape, as a system of interacting components, structures, and processes, varies in space and time.

landscape ecology. The science and art of studying and influencing the relationship between spatial pattern and ecological processes on multiple scales. Land use and land cover change and its ecological consequences are key research topics in this discipline.

landscape fragmentation. The breaking up of vegetation or other land cover types into smaller patches by human activities, or the human introduction of barriers that impede flows of organisms, energy, and material across a landscape.

landscape function. The manner in which a landscape works as a tightly coupled geochemical–biophysical system to regulate the spatial availability and dynamics of resources.

landscape heterogeneity. The mix of different components, structures, and processes occurring in a given landscape, such as how different organisms disperse among different vegetation patches.

landscape pattern. The combination of land cover types and their spatial arrangement in a landscape.

landscape restoration. The actions and processes taken to help damaged landscapes recover toward a specified goal (landform, land use).

landscape system threshold. A point in the dynamics of a landscape where the system changes to a different state, as, for example, a damaged landscape becomes dysfunctional to the point where available resources no longer support a species.

land use. The practices employed on a particular piece of land, such as rotating grazing or intensive maize cultivation.

latent energy exchange. The exchange of energy by the evaporation of water.

late successional species. The species found in an ecosystem that has not experienced a disturbance for a long period of time. Late successional species typically have K-selected traits, such as long generation time, slow rates of growth, long lifespan, and strong competitive ability. As a result, late successional species come to dominate an ecosystem when no further disturbances occur. Compare EARLY SUCCESSIONAL SPECIES.

leaf energy balance. The balance of energy inputs and outputs that influence leaf temperature. Solar radiation is the most important input, and transpirational cooling and convective heat loss are the most important outputs.

life table. A table summarizing age-specific survivorship and fertility, used to calculate the net reproductive rate.

limiting factor. Of the various components of an ecosystem that can potentially restrict the ability of a certain organism or species to grow, survive, and reproduce in that area, the one that is least available at a given time. Limiting factors may be abiotic (e.g., temperature) or biotic (e.g., predators). Also, limiting resource.

limnology. The scientific study of the ecological and physical characteristics of lakes and other inland bodies of water.

lineage. A single line of ancestor–descendent relationship, connecting nodes within a phylogeny.

linkage disequilibrium. A statistical association between alleles at one locus and alleles at a different locus, the consequence of which is that selection on one locus (e.g., a locus affecting an ecological trait such as color pattern) causes a correlated evolutionary response at the other locus (e.g., a locus affecting mating preference).

load. See GENETIC LOAD.

local adaptation. The adaptation of populations to the immediate physical environment or to the resident populations of other species with which they interact.

local competition. Competition among relatives for limiting resources (including mates).

local extinction. See EXTINCTION.

local population. An assemblage of individuals sharing a common environment, competing for the same resources, and reproducing with each other.

longline. A line of considerable length, bearing numerous baited hooks, that is often used in commercial fishing; e.g., for tuna or swordfish. The line is set for varying periods up to several hours at various depths or on the seafloor, depending on the target species. Longlines, which are usually supported by floats, may be 150 km long and have several thousand hooks.

macroecology. The study of how species divide resources (energy) and area at large scales of space and time.

macroparasite. A parasite that grows but does not multiply in its host, producing infective stages that are released to infect new hosts; the macroparasites of animals mostly live on the body or in the body cavities (e.g., the gut); in plants, they are generally intercellular.

Malthusian. Having to do with or reflecting the views of the English economist and demographer Thomas Robert Malthus, especially the proposition that population is naturally limited by the available food supply.

market failure. 1. A situation in which competitive markets do not attain Pareto optimality; i.e., it is not possible to benefit one individual without harming someone else. 2. More generally, any situation in which competitive markets are not able to bring about the efficient and equitable distribution of resources.

mass effects. The quantitative effects of dispersal on local population dynamics. Emigration from a population may have negative effects on its demography, while immigration may have positive (rescue) effects.

matrix. The dominant and most extensive patch type in a landscape, which exerts a major influence on ecosystem processes.

maximum sustained (sustainable) yield (MSY). The highest long-term average yield that can be obtained from a fish stock on a sustainable basis.

megafauna. 1. A term for large-bodied (>44 kg) animals. 2. Specifically, the large mammal biota of the Pleistocene.

mesopredator. A predator that is fed on by another predator, usually a top carnivore.

mesotrophic. Describing lakes that are intermediate in characteristics between oligotrophic and eutrophic lakes. They are moderately well supplied with plant nutrients and support moderate plant growth.

metabolic. Having to do with or involved in METABOLISM.

metabolic rate. The energy expenditure of an organism per unit time. Metabolic rate is normally expressed in terms of rate of heat production (kilojoules per time).

metabolism. A network of chemical reactions that take place in living entities, by which energy and materials are taken up from the environment, transformed into the component of the network that sustains it, and allocated to perform specific functions.

metacommunity. A set of local communities that are linked by the dispersal of its components and potentially interacting species.

metapopulation. 1. A total population system that is composed of multiple local populations geographically separated but functionally connected through dispersal. 2. More specifically, a collection of populations each of which has reasonably high probabilities of local extinction and also of recolonization.

metapopulation capacity. A measure of the size of a habitat patch network, taking into account the total amount of habitat as well as the influence of fragmentation on metapopulation viability.

methanogens. Wetland bacteria that produce methane (CH₄, a greenhouse gas) by decomposing organic matter in anaerobic environments.

microbe. Another term for a MICROORGANISM, especially a disease-causing bacterium.

microbiology. The scientific study of microorganisms.

microevolution. The occurrence of small-scale changes in allele frequencies in a population over a few generations.

microhabitat. A small, localized habitat within a larger ecosystem, used for a specific type of activity (e.g., foraging, oviposition, nesting).

micronutrient. A chemical element necessary in relatively small quantities for organism growth.

microorganism. An organism that is generally too small to be observed without the aid of a microscope, either single-celled or a microscopic cell cluster; e.g., bacteria, cyanobacteria, unicellular algae, fungi, and viruses.

microparasite. A small, often intracellular parasite that multiplies directly within its host.

Millennium Ecosystem Assessment (MA). A five-year effort (2001–5) to assess global trends in ecosystem services and to transform the resulting knowledge into political action to reduce ecological threats worldwide.

mimicry. 1. Evolution by natural selection in which a character is favored because it closely resembles one found in a different species. 2. The fact of different species sharing similarly perceived characteristics in this manner. In Batesian mimicry (named for Henry Walter Bates), the mimic species is a desired prey item that tricks its potential predator by adopting the warning coloration of a similar distasteful or dangerous species. In Müllerian mimicry (named for Hans Müller), two species that are both distasteful or dangerous share common warning systems.

mineralization. The microbially mediated conversion of organically bound nutrients such as nitrogen and phosphorus to soluble inorganic forms that can be taken up by plants.

minimum viable population. The smallest number of individuals in a population required for the population to have a specified probability of persistence over a given period of time.

model. A term for the species whose character is copied by a mimic. See MIMICRY.

modularity. The evolution of developmental constraints by which one of two or more alternative, qualitatively different suites of characters can be activated by particular genetic or environmental cues.

monoculture. 1. An agricultural setting or system in which only one crop is cultivated; e.g., corn. 2. Any area in which a single plant species dominates the landscape. Thus, monocultural.

Monod equation. An equation describing the relationship between substrate concentration and the growth rate of a microbial population. (Developed by Jacques Monod.)

monophyletic. Describing a group of species that are more closely related to each other than any of them are to other species outside the group. Thus, monophyly.

morphology. 1. The observable form and structure of a given organism or taxon, considered as a whole. 2. The study of the form and structure of organisms, especially their external form. Thus, morphological.

MRCA. Most recent common ancestor; the most recent node that is shared by any two taxa in a phylogenetic tree.

MSY. See MAXIMUM SUSTAINED YIELD.

Müllerian mimicry. See MIMICRY.

multiple (stable) state. The existence of one or more alternative ecological communities in a given habitat, persisting over more than a single generation of the dominant species; this is contingent on the history of disturbance events that reset community composition.

mutualism. A two-species interaction that confers survival and/or reproductive benefits to both partners.

mycorrhizae. A relationship of symbiosis between the roots of most higher plants and several groups of fungi, in which the fungal partner typically derives energy from the plant and the plant receives nutrients from the fungus.

natal habitat. The area in which an animal lives immediately after birth.

natural enemy. A species that utilizes another species as a resource and harms that other species in so doing. Natural enemies include true predators, parasites, parasitoids, pathogens, and herbivores.

natural resource. Any feature of the environment that is utilized by humans in its natural state, through activities such as forestry, fishing, and mining.

natural selection. A difference, on average, between the survival or fecundity of individuals with certain phenotypes compared with individuals of the same species with other phenotypes.

neritic. Having to do with or inhabiting the shallow pelagic zone over the continental shelf, i.e., waters less than 200 m deep, and deeper waters in areas of coastal submarine slopes.

net ecosystem production. The amount or rate of organic material produced by green plants after both autotrophic and heterotrophic respiration.

net primary production (NPP). The biological productivity of the landscape, that is, the rate of conversion in a given location of physical energy (sunlight) into biological energy (through photosynthesis), in the form of organic carbon that becomes available for other trophic levels in the ecosystem.

net reproductive rate. The average number of offspring to which a newborn female gives birth over her entire life.

neutral dynamic. A variation in community composition determined by stochastic effects of dispersal and demography among species with equivalent niches.

neutrality. A term for the assumption of equivalence in individuals’ prospects of reproduction or of death, irrespective of the species they belong to.

neutral theory. The principle that genetic change is primarily the result of mutation and genetic drift, and that different molecular genotypes are neutral with respect to each other.

niche. The specific role and requirements of a particular population or species within a larger community.

niche complementarity. A condition in which different niches result in variation in the utilization of resources or space.

niche construction. The modification of local resource distributions by organisms so as to influence both the ecosystem and the evolution of resource-dependent traits.

niche dimension. An environmental variable along which a species’ niche is characterized, such as food size; typically represented as the axis of a graph.

nitrification. The biologically mediated oxidation of ammonium (NH₄) to nitrate (); specialized microorganisms derive their energy from this transformation.

nitrogen fixation. A process by which inert atmospheric dinitrogen (N2) is converted into chemical forms (e.g., nitrate, ammonia) that can be used by organisms. Nitrogen fixation is carried out by certain microorganisms.

nonadaptive radiation. An elevated rate of speciation in the absence of noticeable ecological shifts.

nonaptation. A term for a character that cannot be selectively distinguished from contrasting conditions present in the evolutionary history of a population.

non-point-source pollution. Pollution that comes from many diffuse sources and that is carried by rainfall or snowmelt as it moves over or through the ground to fresh water. These pollutants include excess fertilizers, herbicides from agricultural or residential areas, oils or other toxic chemicals from urban runoff, or salt from roads or irrigation practices. Compare POINT-SOURCE POLLUTION.

nontrophic interaction. A direct interaction that changes the behavior, morphology, or chemical composition of a species in response to the threat of being consumed.

nonuse value. The value of an allocation that benefits someone other than the user, deriving from the fact that the user cares for the beneficiary. The beneficiary may be some other species or a member of a future generation.

nullcline. A set of points in an ecological model where the rate of change of one species is zero (at equilibrium). In community models, intersections of nullclines indicate points where more than one species is at equilibrium.

numerical response. The relationship between the number of predators in an area and prey density.

numerical stability. A steady-state equilibrium in population size; i.e., the numbers of individuals to which a system will return if it is perturbed; stability in predator–prey systems refers to the numerical stability of both predator and prey that allows them to coexist indefinitely.

nutrient. One of the organic or inorganic raw materials required for the growth and survival of an organism; e.g., nitrogen, phosphorus, iron, or vitamins.

nutrient concentration. The percentage of a given element such as nitrogen and phosphorus within producer biomass or detritus on a dry weight basis.

nutrient content. The quantity of an element in an organism’s biomass. This may be measured as moles or grams per organism, as the percentage of mass made up by a given element, or as the X:C ratio where X is a nutrient such as N or P.

nutrient foraging. The noncognitive foraging behaviors of plants to influence the uptake of water, light, nitrogen, and other nutrients, as by adjusting allocations to roots and shoots or altering uptake kinetics.

nutrient limitation. A condition that occurs when the rate of a biological process such as productivity or decomposition is constrained by a low supply of one or more biologically essential elements.

objective function. A mathematical statement of quantities to be maximized (as in the case of the number of species or other biodiversity elements meeting targets) or minimized (e.g., cost).

obligate mutualism. A type of mutualism without which an organism will fail to survive and/or reproduce.

oceanic conveyor belt. An oceanic circulation pattern driven by temperature and salinity gradients to move warm and cold water around the globe, thus moderating temperatures and salinity patterns.

oligotrophic. Describing a condition of low nutrient concentration and low standing stock of living organisms. Oligotrophic lakes are poorly supplied with plant nutrients and support little plant growth. Thus, oligotrophy.

omnivorous. Describing an animal that feeds on both plants and other animals as a primary food source. Such an animal is an omnivore.

omnivory. The fact of feeding at more than one trophic level, such as occurs when a predator consumes herbivores as well as other predators.

outbreeding depression. A decline in fitness resulting from mating among distantly related individuals (as from the disruption of coadapted gene complexes).

overexploitation. The excessive, unsustainable use of a natural resource by humans, to the extent that the resource becomes depleted, or, in the case of wildlife, suffers extinction or loss of genetic diversity.

overfishing. Fishing activities that deplete a fishery to a point beyond the capacity of species to reproduce and maintain their population; e.g., the overfishing of cod in the Baltic Sea.

oviposition. The act of laying an egg on or in a host.

ovipositor. The specialized structure in many adult female parasitoids that allows them to lay an egg on or in a host.

pandemic. 1. An outbreak of a disease that spreads globally or throughout a very large region. 2. A species with a very large geographic range.

parasite. An organism that resides within or on another organism and is nutritionally dependent on that organism.

parasitoid. An insect in which the adult female lays one or more eggs on, in, or near the body of another insect (the host), and the resulting parasitoid offspring use the host for food as they develop, killing the host in the process.

Pareto optimality or optimum. An equilibrium situation in which economic resources and output are allocated so efficiently that no individual can be made better off without at least one other individual becoming worse off. (Described by economist Vilfredo Pareto.)

particulate matter. A term for organic matter derived from the degradation of dead organisms, consisting of materials such as leaf pieces, wood, animal body parts, and so on.

pasture. Agricultural land used for animal grazing, officially defined as land used permanently for herbaceous forage crops, either cultivated or growing wild.

patch. A relatively homogeneous area within a landscape that differs markedly from its surroundings in its biotic and abiotic structure and composition.

patch dynamics. The perspective that ecological systems are mosaics of patches exhibiting nonequilibrium transient dynamics and together determining system-level structure and function.

patch network. A series of discrete patches in a fragmented landscape, each of which may be occupied by a local population, and which together make up a system that may be occupied by a metapopulation.

pathogen. An infectious agent or parasite that causes illness in its host, usually defined as clinical illness, i.e., significant pathology or damaging physiological change. Thus, pathogenic.

pelagic. Having to do with environments or organisms of the open ocean, specifically the surface or middle depths of the oceans rather than the bottom.

per capita growth rate. The rate at which a population changes per individual in the population, as a result of reproduction, mortality, emigration, and immigration.

performance. A quantitative measure of the capability of an organism to conduct an ecologically relevant task such as sprinting, jumping, or biting.

persistence. The sustained existence of species or other elements of biodiversity both within and outside of conservation areas.

phenology. The timing of recurring biological phenomena, ranging from annual budburst and senescence in plants to the onset of animal migrations, egg laying, and metamorphosis. Thus, phenological.

phenotype. The outward characteristics of organisms, such as their form, physiology, and behavior.

phenotypic plasticity. The ability of an individual to express different features (i.e., alter its phenotype) in response to different environmental conditions.

phoresis. A mechanism of dispersal involving the attachment of the organism or a part to another actively dispersing organism. Thus, phoretic.

photoautotroph. An organism that converts inorganic carbon to organic materials and therefore does not need to ingest or absorb other living things. Green plants (as well as certain algae and cyanobacteria) are photoautotrophs because they use light energy to make this conversion.

photoautotrophy. A mode of nutrition by which an organism can reduce inorganic carbon to organic matter using light energy. Thus, photoautotrophic.

photosynthesis. The fundamental chemical process in which green plants (and blue-green algae) utilize the energy of sunlight and other light to convert carbon dioxide and water into carbohydrates, with chlorophyll acting as the energy converter. This releases oxygen and is the chief source of atmospheric oxygen. Photosynthesis provides green plants with their complete energy requirement and allows other organisms to obtain their own nutrients from these plants, either directly or indirectly.

photosynthetic. Relating to or involved in a process of photosynthesis.

photosynthetic pathways. Alternative photosynthetic pathways (C3, C4, and CAM) that differ in underlying biochemical and physiological mechanisms, resulting in contrasting performance depending on temperature and the availability of light, water, and nutrients.

phylogenetic clustering/overdispersion. The tendency of species to be on average more (or less) evolutionarily related in a sample than in the larger species pool.

phylogenetic distance. In a phylogenetic tree, the sum of branch lengths from one tip (or internal node) down to the MRCA (most recent common ancestor) and back up to another tip (or node).

phylogenetics. The scientific study of the evolutionary relationships within and between groups.

phylogenetic tree. A branching diagram showing the hierarchy of evolutionary relationships among a group of taxa (extant and/or extinct). Terminal taxa or tips are connected by branches to internal nodes that indicate a hypothesized ancestor. A clade includes all of the taxa (extant and extinct) that descend from a node.

phylogeny. 1. The evolutionary history of a species or other taxonomic group. 2. See PHYLOGENETIC TREE.

phytoplankton. Microscopic, mostly single-celled photosynthetic organisms living in the ocean or another body of water where they drift with the currents.

phytosociology. The study of the organization and distribution of plant communities.

planetary boundary layer (PBL). The lowest part of the Earth’s atmosphere where the surface influences wind movements, humidity, and temperature over time periods of about 1 hour and up to 1–2 km above the surface.

plankton. A collective term for various drifting organisms of the pelagic zone. Phytoplankton are photosynthetic primary producers, and zooplankton are consumers.

planula. The free-swimming larva of corals. Planulae are released directly by brooded corals following internal fertilization.

pleiotropy. The multiple phenotypic effects of a gene (e.g., a gene affecting color pattern that also affects mating preferences). Thus, pleiotropic.

point-source pollution. Pollution that comes from clearly identifiable local sources, such as outlet pipes from waste water treatment plants or other industrial sources. Compare NON-POINT-SOURCE POLLUTION.

policing. A term for actions by group members that suppress or punish selfish behavior by other group members.

polyculture. An agricultural system in which multiple crops are grown on the same unit of land at the same time.

polygyny. A mating system in which a few males monopolize many females.

polymorphism. The existence of two or more forms in the same population that differ in morphology or some other way.

population. A group of individuals of the same species occupying a certain geographic area over a specified period of time.

population cycles. Changes in the numbers of individuals in a population that repeatedly oscillate between periods of high and low density.

population dynamics. The variation in time and space in the size and density of a population.

population genetics. The study of the genetic composition of biological populations, the factors that lead to changes in this genetic composition over time, and the ways in which these changes affect evolution and speciation.

population growth rate. The per capita rate at which a population changes size over time, typically computed as the birthrate minus the death rate.

population regulation. The tendency of a population to persist within bounds.

population viability. See VIABILITY.

population viability analysis (PVA). A formal process of identifying the threats faced by a species and evaluating the likelihood that the species will persist for a given time into the future.

postmating isolation. Barriers to gene flow that act after mating; e.g., intermediate trait values of hybrids that make them poor competitors for resources, reducing their fitness.

predator. A natural enemy that kills its victim in order to utilize resources contained in that victim.

predator–prey relationship. The ongoing ratio in a given habitat of the population size of a predator and that of its target prey.

premating isolation. Barriers to gene flow that act before mating; e.g., divergent mate preferences that prevent copulation between individuals from different populations.

primary producer. An organism capable of converting atmospheric carbon dioxide into organic matter; an AUTOTROPH.

primary production or productivity. The production of new living material by autotrophs (e.g., plants, algae), most commonly through photosynthesis. Compare SECONDARY PRODUCTION.

private good. A commodity whose consumption by one agent reduces the amount of the good available for use by others; e.g., a loaf of bread. Compare PUBLIC GOOD.

private optimum. The allocation that optimizes a private decision maker’s objective function. If there are externalities, this will be different from the SOCIAL OPTIMUM.

producer–scrounger games. A term for the contrasting behavior patterns in socially foraging animals of either searching for their own food (producer) or searching for opportunities to join the food discoveries of others (scrounger).

production function. A real-valued function that shows the maximum amount of output that can be produced for any given combination of inputs.

propagule. Any part of an organism used for the purpose of dispersal and propagation.

provisioning services. Tangible and consumable items humans derive from ecosystems, such as food, fiber, fuel, and fresh water.

pseudointerference. A form of temporal density dependence in which the parasitoid efficiency decreases at high parasitoid densities because an increasing fraction of parasitoid attacks are wasted on already parasitized hosts.

public good. A commodity whose consumption by one agent does not preclude the availability of the same amount for use by others; e.g., clean air. Compare PRIVATE GOOD.

purse seine. A large fishing net used to encircle surface-schooling fish such as mackerel or tuna. The net may be of a size up to 1 km length and 300 m depth. Purse seines are so called because during retrieval, the lower part of the net is closed (or pursed) by drawing a line through a series of rings to prevent the fish from escaping.

PVA. See POPULATION VIABILITY ANALYSIS.

quantitative trait. A trait that shows continuous rather than discrete variation; such traits are determined by the combined influence of many different genes and the environment.

quasiextinction. The fact of a population collapsing to the point where extinction is likely to occur in the foreseeable future if existing conditions and trends persist.

quasiextinction threshold (N_qe). The minimum number of individuals below which a population is likely to be critically and immediately imperiled.

Quaternary period. The geologic time period beginning roughly 1.8 million years before present.

random walk. In population genetics, a change in allele frequencies from their initial values as a result of repeated episodes of genetic drift.

range edge or limit. The outermost geographic occurrences of a species, usually excluding vagrant individuals.

rarefaction curve. The statistical expectation of the number of species in a survey or collection as a function of the accumulated number of individuals or samples, based on resampling from an observed sample set.

recharge. The movement of surface water (e.g., rainwater) below ground into an aquifer.

redox reaction. One of a class of chemical reactions that involve the transfer of electrons with or without protons (i.e., hydrogen atoms); a contraction of the terms reduction (addition of electrons or hydrogen atoms to a molecule) and oxidation (removal of electrons or hydrogen atoms from a molecule).

reductionism. An analytical approach by which understanding of complex systems can be obtained by reducing them to the interactions among their constituent parts. Thus, reductionist.

regime. The specific, relatively stable state of a given ecosystem.

regime shift. A relatively rapid transition from one persistent dynamic regime to another; e.g., from a grassy savanna with low shrub biomass to a woody savanna with low grass biomass.

regulating services. Benefits obtained from the regulation of ecosystem processes, including disease regulation, climate regulation, erosion regulation, and pollination.

rehabilitation. See RESTORATION.

relative abundance. The quantitative pattern of rarity and commonness among species in a sample or a community.

remote sensing. The indirect measurement of habitat characteristics, for example by Earth-orbiting satellites.

renewable. Describing resources that are able to regenerate themselves within a relatively short time frame through natural processes. For example, wind energy and hydro-power are renewable resources; a natural gas deposit or a coal seam is nonrenewable; a forest or a fish stock is potentially renewable but may become nonrenewable if overexploited.

replacement technology. See SUBSTITUTE TECHNOLOGY.

representation. A term for a sampling of biodiversity pattern, such as a number of species occurrences, within the boundaries of conservation areas.

reproductive isolation. A reduction or lack of genetic exchange (gene flow) between taxa.

reproductive success. The number of an animal’s offspring that survive to maturity, relative to the number produced by others in the same population.

reservoir host. A host that can harbor human pathogenic organisms without acquiring the disease and thus serve as a source from which an infectious disease may spread.

resilience. The ability of an ecosystem to recover from or resist disturbances and perturbation, so that the key components and processes of the system remain the same.

resilient. Describing ecosystems that are able to maintain, or restore, essentially the same state when subject to disturbance or rapid change.

resistance. 1. The ability of an ecosystem to withstand disturbance without major change in structure and function. 2. The ability of an individual organism to limit or suppress the effects of an infectious disease.

resource. Any aspect of the environment that may be consumed by one individual such that it is no longer available to another organism; e.g., resources for plants include nutrients such as nitrogen, phosphorus, and potassium, along with light, water, and carbon dioxide.

response capacity. The ability of a local community to respond to changes in environmental drivers.

restoration. The process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed.

restoration ecology. The study of the ways in which active human intervention can aid in the recovery of disturbed ecosystems.

richness. See SPECIES RICHNESS.

richness estimator. A statistical estimate of the true species richness of a community or larger sampling universe, including unobserved species, based on sample data.

saltation. The evolution of a large, qualitative change in phenotype in a single mutational step. Compare GRADUALISM.

scale. The physical dimensions, in either time or space, of a phenomenon or observation.

scale insect. Any of various plant-sucking insects that stay attached to a plant for almost their entire life history.

scrounger. See PRODUCER–SCROUNGER GAMES.

seamount. An elevation rising 1000 m or more from the sea floor with limited extent across the summit.

secondary production. The production of new living material through tissue produced by heterotrophs (e.g., fish); so called because these organisms rely on the consumption of living or dead organic material of other organisms. Compare PRIMARY PRODUCTION.

selection. See NATURAL SELECTION.

selection effects. The influence that species have on ecosystem functioning simply through their species-specific traits and their relative abundance in a community. Positive selection effects occur when species with higher-than-average monoculture performance dominate communities. Negative selection effects involve the dominance of species that do not contribute significantly to ecosystem functioning.

selection gradient. A measure of the strength of selection acting on quantitative traits.

selective sweep. Favorable directional selection that results in a region of low genetic variation closely linked to the selected region.

selfish genetic elements. Genes that spread at a cost to the organism; stretches of DNA that act narrowly to advance their own proliferation or expression and typically cause negative effects on nonlinked genes in the same organism.

selfishness. Behavior that benefits the individual performing it at a cost to one or more other individuals.

self-organization. In social species, the spontaneous development of group organization, without central control, because of the actions and interactions of multiple individuals.

semelparous. Describing a reproductive pattern in which individuals reproduce only once in their lives and often die shortly after reproduction. Thus, semelparity.

sensible heat exchange. The exchange of energy as heat.

sexual selection. A difference among members of the same sex between the average mating success of individuals with a particular phenotype and that of individuals with other phenotypes; can be based on factors such as the ability to dominate rivals of the same sex, or attributes that are more attractive to the opposite sex.

shadow price. The social opportunity cost of an ecological resource; i.e., its true value to society. If there are externalities, implying that markets are incomplete, the shadow value will be different from the market price.

shelf. An area at the edge of a continent, below the surface of the ocean, down to a depth of 200 m (approximately 600 ft). Shelves usually are the most productive parts of the ocean and sustain the bulk of the world’s fisheries.

shifting baselines syndrome. The adoption of sliding standards for the health of ecosystems because of lack of experience and ignorance of the historical condition.

shifting transition. A boundary location that shifts back and forth with no net change over time.

sink. 1. A term for any population that consistently receives more immigrants than it sends out emigrants. Contrasted with SOURCE. 2. See CARBON SINK.

sink population. A local population that has negative expected growth rate, and that therefore would go extinct without immigration. Its habitat is termed a sink habitat. Contrasted with SOURCE POPULATION.

social–ecological system. An ecological system and a linked social system of resource users and their governance arrangements (if present).

social foraging. A process of collective feeding by groups of the same or different species. Social foraging may allow for information sharing, PRODUCER–SCROUNGER GAMES, group hunting, task specialization, and, very often, safety in numbers.

social optimum. The allocation that will optimize the social welfare function or index of social well-being.

soil texture. See TEXTURE.

source. Any population that consistently sends out more emigrants than it receives immigrants. Contrasted with SINK.

source population. A local population that has sufficiently high growth rate when small to persist even without immigration. Its habitat is termed a source habitat. Contrasted with SINK POPULATION.

spatial. Having to do with the space or area in which an organism or population is found, or in which an ecological process takes place.

spatial ecology. A discipline that studies the fundamental effects of space on the dynamics of individual species and on the structure, dynamics, and diversity of communities.

spatial refuge. A location where a species or local population is less likely to be affected by its predators, competitors, or pathogens, or by other processes impacting on its survival, growth, and reproduction.

speciation. The process by which new species develop through evolutionary forces.

species. A fundamental category for the classification and description of organisms, defined in various ways but typically on the basis of reproductive capacity; i.e., the members of a species can reproduce with each other to produce fertile offspring but cannot do so with individuals outside the species.

species abundance distribution (SAD). The relative abundance of different species in a given community.

species accumulation curve. The observed number of species in a survey or collection as a function of the accumulated number of individuals or samples.

species–area curve. A graph showing the number of species found in an area as a function of the area’s size.

species–area relation(ship). A relationship that describes how the number of species increases with the area sampled or with the size of the system under analysis; e.g., a lake, habitat fragment, or island.

species diversity. See DIVERSITY.

species richness. 1. The number of species in a community, in a landscape or marinescape, or in a region. 2. The fact of having a relatively large diversity of species in a given ecosystem.

species sorting. Variation in community composition determined by the optimization of fitness among species across patches.

stability. The fact of being stable; the ability of an ecological entity to maintain an equilibrium state, or to return to some previous equilibrium state following a perturbation; e.g., a population whose variability is small relative to the level of environmental variability in its habitat.

stable coexistence. The status of competing species that are able to maintain positive abundances in the long term and are able to recover from perturbations that cause them to deviate from their long-term or steady-state abundances.

stable point. A level of population to which, if the density is initially near this point, the actual population will move generally closer through time.

state. The prevailing conditions of an ecosystem at a given point in time and space, especially as defined by either the dominant species or composition of species, and associated process rates.

stepping stones. A term for small, unconnected portions of suitable habitat that an organism uses to move from one place to another.

stewardship. The ethical concept that the proper role for humans with respect to the natural environment is to act as a steward, or watchful caretaker.

stochasticity. Random (unpredictable) variability that is described by a probability distribution giving the mean, variance, and other properties of the random process. Thus, stochastic.

stock. A group of individuals of a species that can be regarded as an entity for management purposes; roughly corresponding to a population. See also FISH STOCK.

stock–recruitment relationship. A mathematical description of the number of new recruits to a fishery as a function of the spawning stock size.

substitutability. A condition in which an increase in the price of a certain good or service will induce greater demand for another good or service (the substitute).

substitute technology. A form of technology that can wholly take the place of some aspect of ecosystem services.

succession. The process of vegetation development following a disturbance, often characterized by relatively predictable sequences of species replacement over time.

support(ing) services. Processes that are critical to the support of all other ecosystem services, such as nutrient cycling, primary production, and soil formation.

survivorship. The probability that a newborn survives to or beyond a specified age.

sustainable. Able to be maintained over an extended period of time based on current conditions and practices; e.g., an ecosystem or a renewable resource. Thus, sustainability.

switching. A behavioral response by predators to relative prey abundance, such that common prey are disproportionately attacked.

symbiosis. An interaction (positive, negative, or neutral) in which two species exist in intimate physical association for most or all of their lifetimes and are physiologically dependent on each other. Thus, symbiotic.

sympatric speciation. A geographic mode of speciation in which a single population splits into two species in the absence of any geographic separation, often via disruptive selection. Also known as sympatry.

synergy. A situation in which two agents act together to enhance each other, producing a greater positive effect than could be obtained from their separate individual efforts. Such an interaction is synergistic.

syntrophy. A mutualistic interaction allowing two strains to utilize a substrate that neither could utilize if the other were absent.

systematic conservation planning. A scientific process for integrating social and biological information to support decisionmaking about the location, configuration, and management of target areas designated for the conservation of biological diversity.

target. 1. The explicit, quantifiable outcome desired for each species or other ecological element of interest. 2. The particular prey species that is the focus of a given predator’s efforts at predation.

taxon, plural taxa. Any named group (e.g., Vertebrata, Mammalia, Homo sapiens) at any taxonomic rank (e.g., Kingdom, Class, Species); higher taxa are more inclusive.

taxon cycle. A temporal sequence of the geographic distribution of species, from colonizing to differentiating to fragmenting to specializing.

taxonomy. The scientific discipline that is concerned with the naming and classification of organisms. Thus, taxonomic.

technological augmentation. The increase, through technological intervention, in the production of goods and services that nature provides.

technology. A broad term for both tangible human-made objects, such as tools and machines, and human-devised intangibles for the use of such objects, such as processes, programs, and services.

teleconnection. A cause-and-effect chain that operates through several intermediate steps and that leads to a linkage between two parts of a system which is unexpected or novel.

texture. A description of soil in terms of the proportions of sand (large particles), silt (intermediate-sized particles), and clay (smallest particles). Sandy, loose-textured soils allow rapid water infiltration and fast leaching of nutrients. Denser, clayey soils have poor drainage and poor soil aeration.

thermocline. A thermal or temperature gradient in a thermally stratified lake in summer, occupying the zone between the epilimnion and hypolimnion.

threshold. A situation in which there has been a nonlinear (i.e., sudden or stepped) change in an ecosystem in response to a stress or disturbance; this is often difficult to reverse.

threshold element ratio (TER). The nutrient ratio of an organism’s food when that organism shifts from limitation by one element to limitation by another. For example, in the case of C:P, when food is above the TER, that organism will be limited by P, and when food is below the TER, that organism will be limited by C.

top carnivore. See TOP PREDATOR.

top-down. Describing strategies and efforts for conservation and restoration that rely on large-scale government mandates rather than on individual, localized initiatives.

top-down control. Regulation of ecosystem structure and function by consumers rather than factors such as nutrient supply and primary production at the base of the food chain.

top predator. A predator at the top of the food chain feeding on organisms at lower trophic levels (e.g., mesopredators and herbivores).

trade-off. 1. The relationship between the quantity of one ecosystem service that is used and the quantity of one or more other ecosystem services that can be used. 2. More generally, the loss of one quality or aspect of something in return for gaining another quality or aspect.

trait spectra. The abundance-weighted distribution of particular traits in the community.

transmission threshold. The condition R₀ = 1, where R₀ is the BASIC REPRODUCTIVE NUMBER, which must be crossed if an infection is to spread in a population.

transpiration. The evaporation of water from the leaves, stems, and flowers of plants. Transpiration occurs through small pores, or stomata, on leaf and stem surfaces, which must remain open to take up carbon dioxide.

trawling. A fishing method in which one or a pair of vessels (trawlers) tow a large bag-shaped net (trawl net) either along the sea floor or in midwater. Although this is a relatively old method of fishing for many species of fish, bottom trawling is currently questioned because it destroys habitats and catches many nontarget species, which often are subsequently discarded.

trophic. Having to do with food or feeding, especially the feeding of one species on another.

trophic cascade. Reciprocal predator–prey effects that alter the abundance, biomass, or productivity of a community across more than one trophic link in the food web; e.g., removing predators enhances herbivore density, which in turn diminishes plant biomass.

trophic interaction. A direct interaction between species in an ecosystem involving the consumption of a resource species by a consumer species.

trophic level. The position of a given species in the chain of energy or nutrients. In a three-level chain, the top level is taken by predators, the second level by herbivores, and the bottom level by plants.

trophic link. A feeding relationship between two species in an ecosystem.

turnover event. A process of extinction and recolonization in a local population.

unfished biomass. See VIRGIN BIOMASS.

unstable equilibrium. The condition of a population that has moved away from equilibrium following a perturbation. The result may be cycles in abundance, extinction, or chaos, in which the densities are always bounded, but there are no repeated sequences of abundance.

upwelling. An oceanographic phenomenon in which wind induces a transport of water, usually away from a coast, with this water being replaced by water “welling up” from deeper layers. Because the upwelled water is nutrient-rich, upwellings belong to the most productive marine ecosystems.

use value. The value of resources when used by the valuer, as opposed to the value of resources that are used by someone other than the valuer (nonuse values).

utility function. A real-valued function showing that if a consumer prefers the bundle of goods x to the bundle of goods y, then the utility of x is greater than the utility of y.

vagility. An organism’s ability to move through the landscape.

vector. An organism carrying parasites from one host individual to another, within which there may or may not be parasite multiplication.

vector-borne disease. Infectious diseases spread indirectly via an insect or rodent; e.g., malaria, dengue fever, West Nile virus, plague, Hantavirus. Often, part of a pathogen’s life cycle occurs within the insect vector.

viability. The probability of continued existence of a population. Viability is the converse of the risk of extinction (often defined in terms of QUASIEXTINCTION rather than complete extinction) over some time period.

viable. Describing any population that can persist through time by a combination of local recruitment and immigration.

virgin biomass. 1. The average fish stock size in an unexploited condition. 2. Living vegetation potentially available for use as an energy source.

virtual water. The volume of water that circulates in an economic system as an embedded ingredient of food and other traded products; a concept based on the idea that arid countries compensate for water deficits by importing water-intensive commodities rather than domestically producing these commodities.

water mass. A portion of the marine environment having a characteristic average value of temperature and salinity that is related to its origin and global circulation pattern.

water/nutrient efficiency. The efficiency of photosynthesis relative to investment of water or nutrients.

watershed. All of the land area from which water that drains from it or is under it flows to a certain lower point such as a river or the ocean.

weathering. The breakdown of rocks and minerals, at least partially into soluble and biologically available components.

wildlife. A broad term for all uncultivated plants and undomesticated animals living freely in nature, especially vertebrates such as mammals, birds, reptiles, and amphibians.

within-system cycle. Transfers of nutrients among plants, animals, microorganisms, and soil and/or solution, within the boundaries of an ecosystem.

yield. The number of microbial cells produced per unit of substrate.

zoonosis. An infection that occurs naturally and that can persist in a wildlife species, and that also can infect and cause disease in humans.

zoonotic disease. Describing a disease that can be spread from animals to people, such as rabies or Lyme disease.