2 Productivity and Trophic Structure Free Online FlashCards

What is primary productivity?

Primary productivity is the rate at which producers capture energy and store it as organic matter (biomass).

What determines an organism’s trophic level?

A trophic level is an organism’s feeding position. Producers occupy the first level; primary, secondary, and tertiary consumers feed at successively higher levels.

In a food chain, what does an arrow indicate?

A food-chain arrow points from the food to the consumer, showing the direction energy moves.

How do energy and nutrients differ in ecosystems?

Energy flows through ecosystems, while nutrients cycle.

Why is an energy pyramid always upright?

An energy pyramid shows energy available or transferred at each level over time. It is always upright because energy is lost at each transfer.

What does gross primary productivity measure?

Gross primary productivity (GPP) is the total energy or organic matter generated by producers.

How is net primary productivity calculated?

Net primary productivity is what remains for growth after producer respiration: $\mathrm{NPP}=\mathrm{GPP}-\text{producer respiration}$.

What does NPP measure: a rate or a standing amount of biomass?

NPP is a rate of new producer biomass available to consumers, not the total biomass present at one moment.

Why can an omnivore occupy more than one trophic level?

An omnivore that eats both plants and animals can feed at more than one trophic level.

What does a food web show?

A food web connects interrelated food chains and represents feeding relationships in a community more realistically than a single chain.

What do decomposers do in an ecosystem?

Decomposers break down dead organisms and wastes from all trophic levels, returning nutrients to the environment; energy dissipates as heat.

What is the approximate trophic transfer efficiency, and why are food chains usually short?

Roughly 10% of energy at one trophic level becomes production at the next, though the fraction varies. This declining supply helps explain why food chains usually have few levels.