IN CONTEXT
Biology
5th–4th century BCE Ancient Greek writers observe the web of inter-relationships between plants, animals, and their environment.
1866 Ernst Haeckel coins the word “ecology”.
1895 Eugenius Warming publishes the first university course book on ecology.
1935 Alfred Tansley coins the word “ecosystem”.
1962 Rachel Carson warns of the dangers of pesticides in Silent Spring.
1969 Friends of the Earth and Greenpeace are established.
1972 James Lovelock’s Gaia hypothesis presents Earth as a single organism.
The study of the inter-relationship between the animate and inanimate world, known as ecology, only became a subject of rigorous and methodical scientific investigation over the last 150 years. The term “ecology” was coined in 1866 by the German evolutionary biologist, Ernst Haeckel, and is derived from the Greek words oikos, meaning house or dwelling place, and logos, meaning study or discourse. But it is an earlier German polymath named Alexander von Humboldt who is regarded as the pioneer of modern ecological thinking.
Through extensive expeditions and writings, Humboldt promoted a new approach to science. He sought to understand nature as a unified whole, by inter-relating all of the physical sciences and employing the latest scientific equipment, exhaustive observation, and meticulous analysis of data on an unprecedented scale.
The crocodile’s teeth
Although Humboldt’s holistic approach was new, the concept of ecology developed from early investigations of natural history by ancient Greek writers, such as Herodotus in the 5th century BCE. In one of the first accounts of inter-dependence, technically known as mutualism, he describes crocodiles on the River Nile in Egypt opening their mouths to allow birds to pick their teeth clean.
A century later, observations by the Greek philosopher Aristotle and his pupil Theophrastus on species’ migration, distribution, and behaviour provided an early version of the concept of the ecological niche – the particular place in nature that shapes and is shaped by a species’ way of life. Theophrastus studied and wrote extensively on plants, realizing the importance of climate and soils to their growth and distribution. Their ideas influenced natural philosophy for the next 2,000 years.
Humboldt’s team climbed Mexico’s Jorullo volcano in 1803, just 44 years after it first appeared. Humboldt linked geology to meteorology and biology by studying where different plants lived.
"The principal impulse by which I was directed was the earnest endeavour to comprehend the phenomena of physical objects in their general connection, and to represent nature as one great whole, moved and animated by internal forces."
Alexander von Humboldt
Nature’s unifying forces
Humboldt’s approach to nature followed in the late 18th-century Romantic tradition that reacted to rationalism by insisting on the value of senses, observation, and experience in understanding the world as a whole. Like his contemporaries, the poets Johann Wolfgang von Goethe and Friedrich Schiller, Humboldt promoted the idea of the unity (or Gestalt in German) of nature – and of natural philosophy and the humanities. His studies ranged from anatomy and astronomy to mineralogy and botany, commerce, and linguistics, and provided him with the breadth of knowledge necessary for his exploration of the natural world beyond the confines of Europe.
As Humboldt explained, “The sight of exotic plants, even of dried specimens in a herbarium, fired my imagination and I longed to see the tropical vegetation in southern countries with my own eyes.” His five-year exploration of Latin America with the French botanist Aimé Bonpland was his most important expedition. Setting out in June 1799, he declared, “I shall collect plants and fossils, and make astronomical observations with the best of instruments. Yet this is not the main purpose of my journey. I shall endeavour to discover how nature’s forces act upon one another and in what manner the geographic environment exerts its influence on animals and plants. In short, I must find out about the harmony in nature.” And he did just that.
Among many other projects, Humboldt measured ocean water temperature and suggested the use of “iso-lines”, or isothermal lines, to join points of equal temperature as a means of characterizing and mapping the global environment, especially the climate, and then comparing the climatic conditions in various countries.
Humboldt was also one of the first scientists to study how physical conditions – such as climate, altitude, latitude, and soils – affected the distribution of life. With Bonpland’s assistance, he mapped the changes in flora and fauna between sea level and high altitude in the Andes. In 1805, the year after his return from the Americas, he published a now-celebrated work on the geography of the area, summarizing the inter-connectedness of nature and illustrating the altitudinal zones of vegetation. Years later, in 1851, he showed the global application of these zones by comparing the Andean zones with those of the European Alps, Pyrenees, Lapland, Tenerife, and the Asian Himalayas.
Defining ecology
When Haeckel coined the word “ecology”, he too was following in the tradition of viewing a Gestalt (unity) of the living and inanimate world. An enthusiastic evolutionist, he was inspired by Charles Darwin, whose publication of On the Origin of Species in 1859 banished the notion of Earth as an immutable world. Haeckel questioned the role of natural selection, but believed that the environment played an important role in both evolution and ecology.
By the end of the 19th century, the first university course in ecology was being taught by the Danish botanist Eugenius Warming, who also wrote the first ecology textbook Plantesamfund (Plant Ecology) in 1895. From Humboldt’s pioneering work, Warming developed the global geographical subdivision of plant distribution known as biomes, such as the tropical rainforest biome, which are largely based on the interaction of plants with the environment, especially climate.
Individuals and community
Early in the 20th century, the modern definition of ecology developed as the scientific study of the interactions that determine the distribution and abundance of organisms. These interactions include an organism’s environment, encompassing all those factors that influence it – both biotic (living organisms) and abiotic (non-living factors such as soil, water, air, temperature, and sunlight). The scope of modern ecology ranges from the individual organism to populations of individuals of the same species, and the community, made up of populations that share a particular environment.
Many of the basic terms and concepts of ecology came from the work of several pioneer ecologists in the first few decades of the 20th century. The formal concept of the biological community was first developed in 1916 by the American botanist Frederic Clements. He believed that the plants of a given area develop a succession of communities over time, from an initial pioneer community to an optimal climax community within which successive communities of different species adjust to one another to form a tightly integrated and interdependent unit, similar to the organs of a body. Clements’ metaphor of the community as a “complex organism” was criticized at first but influenced later thinking.
The idea of further ecological integration at a higher level than the community was introduced in 1935 with the concept of the ecosystem, developed by the English botanist Arthur Tansley. An ecosystem consists of both living and non-living elements. Their interaction forms a stable unit with a sustaining flow of energy from the environmental to the living part (through the food chain) and can operate on all scales, from a puddle to an ocean or the whole planet.
Studies of animal communities by the English zoologist Charles Elton led him to develop in 1927 the concept of the food chain and food cycle, subsequently known as the “food web”. A food chain is formed by the transfer of energy through an ecosystem from primary producers (such as green plants on land) through a series of consuming organisms. Elton also recognized that particular groups of organisms occupied certain niches in the food chain for periods of time. Elton’s niches include not only the habitats but also the resources upon which the occupying organisms rely for sustenance. The dynamics of energy transfer through trophic (feeding) levels were studied by the American ecologists Raymond Lindeman and Robert MacArthur, whose mathematical models helped change ecology from primarily a descriptive science into an experimental one.
A food chain transfers energy from primary producers (plants and algae that convert the Sun’s energy into food energy) to consumer organisms that eat the plants (such as rabbits and other herbivores), and then to the predators that feed on the consumers.
"This whole chain of poisoning, then, seems to rest on a base of minute plants which must have been the original concentrators."
Rachel Carson
The green movement
A boom in popular and scientific interest in ecology in the 1960s and 1970s led to the development of the environmental movement with a whole range of concerns, stimulated by powerful advocates such as the American marine biologist Rachel Carson. Her 1962 book Silent Spring documented the harmful effects on the environment of man-made chemicals such as the pesticide DDT. The first image of Earth seen from space, taken by Apollo 8 astronauts in 1968, awakened public awareness of the planet’s fragility. In 1969, the organizations Friends of the Earth and Greenpeace were established, with the mission to “ensure the ability of the Earth to nurture life in all its diversity”. Environmental protection, along with clean and renewable energy, organic foods, recycling, and sustainability, were all on the political agenda in both North America and Europe, and national conservation agencies were established based on the science of ecology. Recent decades have seen growing concern over global climate change and its impact on the environment and present ecosystems, many of which are already under threat from human activity.
Rachel Carson (far right) made a significant contribution to the science and public understanding of ecology by drawing attention to the destructive impact of pollution on the environment.
ALEXANDER VON HUMBOLDT
Born in Berlin to a wealthy and well-connected family, Humboldt studied finance at the University of Frankfurt, natural history and linguistics in Göttingen, language and commerce in Hamburg, geology in Freiburg, and anatomy in Jena. The death of his mother in 1796 provided Humboldt with the means to fund an expedition to the Americas from 1799 to 1804, accompanied by botanist Aimé Bonpland. Using the latest scientific equipment, Humboldt measured everything from plants to population statistics and minerals to meteorology.
On his return, Humboldt was fêted across Europe. Based in Paris, he took 21 years to process and publish his data in over 30 volumes, and then synthesized his ideas in four volumes entitled Kosmos. A fifth volume was completed after his death in Berlin, aged 89. Darwin called him “the greatest scientific traveller who ever lived”.
Key works
1825 Journey to the Equinoctial Regions of the New Continent
1845–1862 Kosmos
See also: Jean-Baptiste Lamarck • Charles Darwin • James Lovelock