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Ecosystem

All biotic and abiotic components of an environment interacting as a system.

Biotic

Living components of an ecosystem (plants, animals, fungi, bacteria).

Abiotic

Non-living components of an ecosystem (temperature, water, sunlight, soil, pH).

Predation

Interaction where a predator benefits (+) by consuming prey, which is harmed (–).

Mutualism

Symbiotic interaction where both species benefit (+/+).

Commensalism

Symbiotic interaction where one species benefits (+) and the other is unaffected (0).

Parasitism

Symbiotic interaction where the parasite benefits (+) and the host is harmed (–).

Competition

Interaction where both species are harmed (–/–) by competing for the same limited resource.

Resource partitioning

When competing species reduce overlap by using shared resources at different times, places, or in different ways.

Interspecific competition

Competition between individuals of different species.

Intraspecific competition

Competition between individuals of the same species.

Biome

A large regional ecosystem defined by its climate, with characteristic plants and animals adapted to those conditions.

Permafrost

Permanently frozen soil layer found in the tundra, preventing tree growth.

Carbon cycle

The movement of carbon through atmosphere, living organisms, oceans, and geological reservoirs via photosynthesis, respiration, decomposition, and combustion.

Nitrogen fixation

Conversion of atmospheric N₂ into ammonia (NH₃) by bacteria or lightning; makes nitrogen usable by organisms.

Nitrification

Bacterial conversion of ammonia to nitrites, then to nitrates (usable by plants).

Denitrification

Bacterial conversion of nitrates back to N₂ gas, returning nitrogen to the atmosphere.

Assimilation

The uptake of nutrients (nitrogen, phosphorus) by organisms from the soil or water.

Phosphorus cycle

The movement of phosphorus through rocks, soil, water, and organisms with NO atmospheric component.

Limiting factor

The resource or condition that most restricts growth or productivity in an ecosystem.

Hydrologic cycle

The movement of water through evaporation, condensation, precipitation, infiltration, and runoff, powered by the sun.

Transpiration

The release of water vapor by plants through their leaves; plants actively contribute to the water cycle.

Evapotranspiration

Combined water loss from both evaporation (from surfaces) and transpiration (from plants).

Gross primary productivity (GPP)

The total rate of photosynthesis in a given area; all the solar energy captured.

Net primary productivity (NPP)

GPP minus the energy the plant uses for its own respiration; the energy available to consumers.

Primary productivity

The rate at which producers convert solar energy into organic compounds via photosynthesis.

Trophic level

A feeding position in a food chain (producer, primary consumer, secondary consumer, etc.).

10% rule

Only approximately 10% of energy transfers from one trophic level to the next; the rest is lost as heat.

Food chain

A linear sequence showing who eats whom in an ecosystem.

Food web

An interconnected network of multiple food chains showing energy flow through an ecosystem.

Keystone species

A species whose role in an ecosystem is disproportionately large relative to its abundance; its removal causes major ecosystem changes.

Decomposer

An organism (bacteria, fungi) that breaks down dead organic matter and recycles nutrients back into the ecosystem.

Estuary

A highly productive coastal ecosystem where freshwater meets saltwater, receiving constant nutrient inputs.

Residence time

How long a substance stays in a particular reservoir before moving to another.

Biogeochemical cycle

The pathway by which a chemical element moves through both the biotic and abiotic parts of an ecosystem.

Eutrophication

Enrichment of a water body with nutrients (especially nitrogen and phosphorus), causing algal blooms and oxygen depletion — caused by human disruption of nutrient cycles.

Autotroph

An organism that produces its own food from sunlight or chemicals (e.g., plants, algae); same as producer.

Heterotroph

An organism that must consume other organisms for energy (consumers, decomposers).

Keystone species

A species that has a disproportionately large effect on its ecosystem relative to its abundance.