Ecology Cheat Sheet

The core ideas of Ecology distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Ecosystem

A community of living organisms together with the nonliving components of their environment, interacting as a system through nutrient cycles and energy flows. Ecosystems can range in size from a small tide pool to an entire ocean basin.

Food Web

A complex network of interconnected food chains showing the feeding relationships among organisms in an ecosystem. Unlike a simple food chain, a food web reflects the reality that most organisms consume and are consumed by multiple species.

Biodiversity

The variety of life in a particular habitat or ecosystem, measured at three levels: genetic diversity within species, species diversity within communities, and ecosystem diversity across landscapes. Higher biodiversity generally correlates with greater ecosystem resilience.

Carrying Capacity

The maximum population size of a species that an environment can sustain indefinitely given the available food, water, habitat, and other resources. It is denoted by the letter K in population ecology models.

Ecological Succession

The process of change in the species composition of a community over time following a disturbance. Primary succession occurs on barren surfaces where no soil exists, while secondary succession occurs in areas where a disturbance has destroyed a community but left the soil intact.

Nutrient Cycling

The movement and exchange of organic and inorganic matter back into the production of living organisms. Major biogeochemical cycles include the carbon, nitrogen, phosphorus, and water cycles, each essential for sustaining life on Earth.

Keystone Species

A species that has a disproportionately large effect on its ecosystem relative to its abundance. Removing a keystone species triggers significant changes in ecosystem structure and can lead to the decline or loss of many other species.

Biome

A large-scale biological community classified by its dominant vegetation and characterized by the regional climate, particularly temperature and precipitation patterns. Earth's major terrestrial biomes include tundra, boreal forest, temperate forest, grassland, desert, and tropical rainforest.

Ecological Niche

The role and position a species occupies in its environment, including all of the conditions, resources, and interactions it needs to survive and reproduce. A niche encompasses not just habitat but diet, activity period, reproductive strategy, and relationships with other species.

Trophic Levels

The hierarchical levels in an ecosystem defined by the organism's position in the food chain. Energy is transferred from lower to higher trophic levels, but approximately 90% of energy is lost as heat at each transfer, limiting the number of trophic levels in most ecosystems.

Key Terms at a Glance

Abiotic Factor:A nonliving physical or chemical component of the environment, such as temperature, sunlight, water, wind, or soil composition.

Biodiversity:The variety of life in a particular habitat or ecosystem, measured at genetic, species, and ecosystem levels.

Biogeochemical Cycle:The pathway by which a chemical element or molecule moves through the biotic and abiotic compartments of Earth, such as the carbon, nitrogen, and phosphorus cycles.

Biomagnification:The increasing concentration of a substance, such as a toxin, in the tissues of organisms at successively higher trophic levels.

Biome:A large-scale community of organisms classified primarily by the dominant vegetation and characterized by regional climate patterns.

Biotic Factor:A living component of an ecosystem that influences other organisms, including predators, prey, competitors, parasites, and decomposers.

Carrying Capacity:The maximum population size of a species that an environment can sustain indefinitely given the available resources.

Commensalism:A symbiotic relationship in which one organism benefits while the other is neither helped nor harmed.

Community:All the populations of different species living and interacting in a particular area at a given time.

Decomposer:An organism, such as a fungus or bacterium, that breaks down dead organic material and recycles nutrients back into the ecosystem.

Ecological Niche:The role and position a species occupies in its environment, encompassing its habitat, diet, activity patterns, and interactions with other species.

Ecological Succession:The gradual process by which the species composition of a community changes over time following a disturbance or the formation of new habitat.

Ecosystem:A system formed by the interactions of a community of living organisms with the nonliving components of their environment.

Eutrophication:The enrichment of a body of water with excessive nutrients, often leading to algal blooms, oxygen depletion, and loss of aquatic life.

Food Web:A system of interlocking and interdependent food chains showing the complex feeding relationships within an ecosystem.

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