DSST Environmental Science key terms

The rate at which producers form organic material using light energy in photosynthesis or chemical energy in chemosynthesis, measured within a defined system and time period.

Gross primary productivity minus the energy producers consume in their own respiration; the energy actually available to consumers and decomposers as biomass accumulates.

The feeding positions in a food chain, from producers at the first level through primary, secondary, and tertiary consumers, each transferring only a fraction of its energy upward.

The ecological generalization that roughly ten percent of energy at one trophic level is passed to the next, so food chains rarely support more than four or five levels.

The pathway by which an element such as carbon, nitrogen, phosphorus, or water moves among living organisms and the atmosphere, soil, rock, and oceans over time.

Conversion of atmospheric nitrogen gas into ammonia or related compounds by bacteria, lightning, or industrial processes, making nitrogen usable by living organisms.

Nutrient enrichment, usually by nitrogen and phosphorus runoff, that triggers algal blooms whose decay consumes dissolved oxygen and can create dead zones.

The maximum population size of a species that a given environment can sustain indefinitely given available food, water, habitat, and other limiting resources.

Population increase at a constant per-capita rate, producing a J-shaped curve when resources are abundant and no significant limits apply.

Population growth that slows as the population approaches carrying capacity, producing an S-shaped curve because resources become limiting.

Any resource, condition, or interaction that restricts population growth or distribution, such as food supply, predators, disease, or a specific nutrient.

The principle that growth is constrained not by total resources but by the single scarcest essential factor, even when all others are abundant.

A graph showing the number of males and females in each age class of a population, used to project future growth and dependency needs.

The average number of children a woman would bear over her lifetime at current age-specific birth rates, a key driver of population growth.

A model describing the shift of a population from high birth and death rates to low ones as a society develops economically and medically.

The number of different species present in a community, one component of biodiversity that ignores how evenly individuals are distributed among those species.

The relative abundance of individuals among the species in a community; communities with similar abundances have high evenness and generally higher diversity.

A region with exceptionally high numbers of endemic species that has already lost a large share of its original habitat, making it a conservation priority.

A species found naturally in only one restricted geographic area and nowhere else, making it especially vulnerable to habitat loss and invasive species.

A non-native organism introduced to an area where it spreads rapidly, outcompetes native species, and disrupts ecosystem function, often lacking natural predators.

The breakup of continuous habitat into smaller, isolated patches by roads, development, or clearing, reducing gene flow and increasing extinction risk.

Altered conditions, such as more light, wind, and predator access, along the boundary between two habitat types, which can degrade remaining habitat fragments.

The gradual, directional change in species composition of a community over time, from pioneer species toward a more stable climax community.

The first organisms to colonize bare or disturbed substrate, such as lichens and mosses, which help build soil for later successional species.

The relatively stable, late-successional assemblage of species that develops when a site's conditions and disturbance regime remain largely unchanged.

A species whose influence on community structure is disproportionately large relative to its abundance; its removal triggers major ecosystem changes.

Indirect effects that ripple through a food web when a predator's abundance changes, altering populations at lower trophic levels and sometimes vegetation.

An organism whose presence, absence, or condition reveals environmental conditions such as pollution levels or habitat quality, because it is sensitive to change.

The amount of dissolved oxygen consumed by microbes decomposing organic matter in water; high values signal organic pollution and threaten aquatic life.

A condition in which dissolved oxygen in water falls so low that most animal life cannot survive, often caused by nutrient-driven algal decay.