Idea or model
Food chains and webs
Who eats whom in an ecosystem. Energy and nutrients pass from producers to the animals that eat them.
Ecology
How living things interact with each other and their environment.
Ecology is the study of how living things interact with each other and with the places they live.
Ecologists study food webs, energy flow, populations and communities, and how ecosystems respond to change.
Topics include population dynamics and predator-prey models, trophic cascades and keystone species, primary production and the carbon cycle, and biodiversity loss in a changing climate.
Big questions
- What controls how many animals an ecosystem can support?
- What happens when a top predator disappears?
- How is climate change moving species?
Key ideas
Open any idea in the knowledge graph to see what it connects to, here and in other fields.
Process
Energy flow
Energy enters most ecosystems as sunlight and is lost at each step up a food chain, which limits how many levels it can support.
Process
Primary production
Carbon fixed by plants, algae and photosynthetic microbes: about 105 billion tonnes a year worldwide, roughly half on land and half in the ocean.
Process
Trophic cascade
Effects that ripple down a food chain, as when predators hold herbivores in check and plants flourish.
Idea or model
Keystone species
A species, often a predator, that strongly shapes its whole community. Robert Paine introduced the term in 1969.
Idea or model
Population dynamics
How population sizes change through births, deaths and interactions such as predation. Mathematical predator-prey models date to the 1920s.
Idea or model
Functional response
How a predator's feeding rate changes with prey density. It often levels off when prey are plentiful.
Idea or model
Paradox of enrichment
In some predator-prey models, adding resources makes population cycles larger and less stable instead of simply raising every population.
Process
Carbon cycle
The movement of carbon among the air, oceans, living things, soils and rocks.
Idea or model
Biodiversity
The variety of life, from genes to ecosystems. A 2019 global assessment found that around 1 million animal and plant species are threatened with extinction.
Idea or model
Climate change and living things
Warming is moving species ranges: a 2003 analysis found shifts toward the poles averaging 6.1 km per decade and spring events arriving 2.3 days earlier per decade.
Explore it in the labs
Simulation
Change temperature, rainfall, soil and populations in a plant, herbivore and predator food chain, and watch the whole web respond.
- Ecology
- Plant Biology
- Evolution
Interactive explorer
Follow water, sugar and gases through a plant, test what limits photosynthesis, and match hormones to their effects.
- Plant Biology
- Biochemistry
- Ecology
Interactive explorer
Compare bacteria, archaea, fungi, protists and viruses side by side, and model how a bacterial culture grows.
- Microbiology
- Evolution
- Immunology
Current research
Search published papers and preprints in Ecology, with clear labels for reviews, primary research, clinical trials and preprints.
Search papers in EcologySources & further reading
The explanations on this page are our own summaries of these sources. Follow a link to read the original; if anything here disagrees with it, the original wins. How we choose and check sources.
Biology 2e (opens the original in a new tab)
OpenStax (2018). OpenStax, Rice University.
Free introductory college textbook.
TextbookEducationalLicence: CC BY-NC-SA 4.0 (linked, not reused)
Summary for policymakers of the global assessment report on biodiversity and ecosystem services (opens the original in a new tab)
IPBES (2019). Zenodo. Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services.
Consensus reportIntergovernmental sourcePrimary production of the biosphere: integrating terrestrial and oceanic components (opens the original in a new tab)
Field CB, Behrenfeld MJ, Randerson JT, et al. (1998). Science 281:237-240.
Global net primary production of about 105 petagrams of carbon per year, split roughly evenly between land and ocean.
Peer-reviewedPrimary researchFood web complexity and species diversity (opens the original in a new tab)
Paine RT (1966). The American Naturalist 100:65-75.
Removing a predatory sea star from rocky shores reduced the number of species present.
Historical paperPrimary researchSea otters: their role in structuring nearshore communities (opens the original in a new tab)
Estes JA, Palmisano JF (1974). Science 185:1058-1060.
Historical paperPrimary researchTrophic cascades in Yellowstone: the first 15 years after wolf reintroduction (opens the original in a new tab)
Ripple WJ, Beschta RL (2012). Biological Conservation 145:205-213.
Peer-reviewedReviewDoes restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system (opens the original in a new tab)
Hobbs NT, Johnston DB, Marshall KN, et al. (2024). Ecological Monographs 94.
Field experiments questioning how fully wolf reintroduction restored Yellowstone's streamside vegetation.
Peer-reviewedPrimary researchA note on trophic complexity and community stability (opens the original in a new tab)
Paine RT (1969). The American Naturalist 103:91-93.
Introduced the term keystone species.
Historical paperPerspectiveFluctuations in the abundance of a species considered mathematically (opens the original in a new tab)
Volterra V (1926). Nature 118:558-560.
One of the founding mathematical models of predator-prey cycles.
Historical paperTheory or modelWhat drives the 10-year cycle of snowshoe hares? (opens the original in a new tab)
Krebs CJ, Boonstra R, Boutin S, et al. (2001). BioScience 51:25-35.
Real population cycles involve food, predators and more; simple two-species models leave much out.
Peer-reviewedReviewSome characteristics of simple types of predation and parasitism (opens the original in a new tab)
Holling CS (1959). The Canadian Entomologist 91:385-398.
Introduced the functional response: how a predator's feeding rate saturates as prey become abundant.
Historical paperPrimary researchParadox of enrichment: destabilization of exploitation ecosystems in ecological time (opens the original in a new tab)
Rosenzweig ML (1971). Science 171:385-387.
In some models, adding resources makes predator-prey cycles larger and less stable.
Historical paperTheory or modelThe Carbon Cycle (opens the original in a new tab)
NASA Earth Observatory. NASA Science. National Aeronautics and Space Administration.
ReferenceGovernment sourceEducationalNature's Dangerous Decline 'Unprecedented'; Species Extinction Rates 'Accelerating' (opens the original in a new tab)
IPBES (2019). IPBES media release. Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. Published 2019-05-06.
Announces the 2019 global assessment, including its estimate of around 1 million species threatened with extinction.
Fact sheetIntergovernmental sourceA globally coherent fingerprint of climate change impacts across natural systems (opens the original in a new tab)
Parmesan C, Yohe G (2003). Nature 421:37-42.
Peer-reviewedSystematic analysisSummary for Policymakers. In: Climate Change 2022: Impacts, Adaptation and Vulnerability (Working Group II, Sixth Assessment Report) (opens the original in a new tab)
Intergovernmental Panel on Climate Change (2022). IPCC Sixth Assessment Report. Intergovernmental Panel on Climate Change.
Consensus reportIntergovernmental source