Ecology is the scientific study of the interactions between organisms and their environment, including other organisms. The word was coined in 1866 by the German zoologist Ernst Haeckel from the Greek oikos, meaning “house” or “household”, and logos, meaning “study”. Ecology is literally the study of nature’s household: who lives there, what they need, and how they get along.
Ecology is not the same as environmentalism. Environmentalism is a social and political movement; ecology is a science that provides evidence, whatever the conclusions turn out to be.
What you will learn
- What ecology studies and how it differs from related sciences
- The levels of ecological organisation, from individual to biosphere
- What emergent properties are and why they matter
- How ecologists test ideas using observation, experiments and models
The levels of ecological organisation
Ecologists work at different scales, each with its own questions.
| Level | Definition | Example question |
|---|---|---|
| Individual (organism) | A single living thing | How does a camel cope with water loss? |
| Population | Individuals of one species in one area | Why is the tiger population in Chitwan growing? |
| Community | All the populations of different species in an area | How do lions and hyenas share prey on the Serengeti? |
| Ecosystem | A community plus its physical environment | How does energy and nitrogen move through a grassland? |
| Landscape | A mosaic of connected ecosystems | Can leopards move between forest patches through farmland? |
| Biome | A large region with a characteristic climate and vegetation | Why are deserts found at around 30° north and south? |
| Biosphere | All life on Earth and where it lives | How is the global carbon cycle changing? |
The study of individual species and their environment is sometimes called autecology, and the study of communities and ecosystems synecology. Today most ecologists describe their work by topic instead: behavioural ecology, population ecology, community ecology, ecosystem ecology, landscape ecology, global ecology, and applied fields such as conservation biology and restoration ecology.
Emergent properties
Each level has emergent properties: features that appear only when the parts interact and cannot be predicted from the parts alone. A single tree does not have a canopy microclimate, but a forest does. A single ant cannot build a ventilated nest, but a colony can. A population has a birth rate, a death rate and an age structure; an individual does not.
This is why ecology cannot simply be reduced to physiology or genetics. Understanding a coral reef requires studying the reef as a whole, not just individual corals.
Habitat and niche
Two terms appear throughout ecology:
- A habitat is the place where an organism lives, such as a mangrove forest or an alpine meadow.
- A niche is the role an organism plays and the full set of conditions and resources it needs: what it eats, when it is active, the temperatures it tolerates, and so on. A useful comparison is that the habitat is the organism’s address and the niche is its profession.
We explore niches in more detail in Module 2.
How ecologists do science
Ecologists use three main approaches, often together.
- Observation and description. Long-term monitoring, such as counting tigers with camera traps or recording when birds arrive each spring, reveals patterns. The Serengeti and Yellowstone have been studied for decades.
- Experiments. Ecologists test cause and effect by changing one factor. Field experiments include fencing out grazers to see how vegetation changes, or removing a predator from a rock pool. The ecologist Robert Paine’s removal of the starfish Pisaster from rocky shores in Washington State in the 1960s showed that a single predator can maintain the diversity of a whole community, and gave us the term keystone species.
- Models. Mathematical and computer models describe how systems might behave, such as how a population grows or how a disease spreads. Models generate predictions that can be tested with data.
Like all scientists, ecologists form hypotheses, make predictions, collect data and use statistics to judge whether the evidence supports their ideas. Because ecosystems are complex and experiments can be hard to replicate, ecologists pay close attention to sample size, controls and confounding factors.
A short history of ecology
- 1859: Charles Darwin’s On the Origin of Species frames organisms as shaped by their environment and by each other.
- 1866: Ernst Haeckel coins the word Oekologie.
- 1927: Charles Elton’s Animal Ecology introduces food chains, food webs and the pyramid of numbers.
- 1935: Arthur Tansley introduces the term ecosystem.
- 1942: Raymond Lindeman’s study of a Minnesota lake establishes the trophic-dynamic view of energy flow.
- 1953: Eugene and Howard Odum’s Fundamentals of Ecology becomes the field’s defining textbook.
- 1962: Rachel Carson’s Silent Spring shows the ecological effects of pesticides.
- 1967: Robert MacArthur and E.O. Wilson publish the theory of island biogeography.
- Today: satellite data, DNA methods, animal tracking and global data networks allow ecology at planetary scale.
Case study: the Serengeti as a living laboratory
The Serengeti shows every level of ecology at once. Individual wildebeest must find enough grass and water. The wildebeest population grew from about 250,000 in the early 1960s to over a million by the late 1970s after a cattle disease, rinderpest, was eliminated. That increase changed the whole community: more grazing meant less dry grass, fewer fires, and more trees. It also supported more lions and hyenas. Scientists have studied these links for over 60 years, making the Serengeti one of the best-understood ecosystems on Earth.
Try it yourself
Pick a small patch of habitat near you, such as a park, garden or pond. Spend 15 minutes listing every organism you can see and one thing each is doing. Then sort your list by level: which observations are about individuals, which about populations, and which about interactions between species?
Common misconceptions
- “Ecology means being eco-friendly.” Ecology is a science. It informs environmental decisions but is not itself a set of values.
- “Nature is always in balance.” Ecosystems constantly change. Populations fluctuate, fires and floods reset communities, and climate shifts over time.
- “An ecosystem is just a place.” An ecosystem is the living community and its physical environment, together with the flows of energy and nutrients between them.
Key terms
- Ecology: the study of interactions between organisms and their environment.
- Population: members of one species living in the same area.
- Community: all the interacting species in an area.
- Ecosystem: a community and its physical environment.
- Emergent property: a feature that arises from interactions between parts.
- Keystone species: a species with an effect on its community far larger than its abundance would suggest.
Quick quiz
Test what you have learned. Scoring 60 percent or more marks this module as complete.
Further reading
- Begon, M., Townsend, C. and Harper, J. Ecology: From Individuals to Ecosystems.
- Paine, R. T. (1966). “Food web complexity and species diversity.” The American Naturalist.