DSST Environmental Science flashcards

30 cards. Read the term and the definition here. The deck at the top of this page is optional.

Primary productivity

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.

Net primary productivity

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

Trophic levels

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.

Ten percent rule

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.

Biogeochemical cycle

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.

Nitrogen fixation

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

Eutrophication

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

Carrying capacity

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

Exponential growth

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

Logistic growth

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

Limiting factor

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

Liebig's law of the minimum

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

Age structure diagram

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

Total fertility rate

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

Demographic transition

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

Species richness

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

Species evenness

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

Biodiversity hotspot

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.

Endemic species

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

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.

Habitat fragmentation

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

Edge effect

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

Ecological succession

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

Pioneer species

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

Climax community

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

Keystone species

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

Trophic cascade

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

Indicator species

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

Biological oxygen demand

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

Hypoxia

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