Primary Productivity, Trophic Levels, and Food Webs

Flashcards covering primary productivity, ecological efficiency, the laws of thermodynamics, the 10% rule, and food web dynamics.

Primary productivity

The rate at which solar energy (sunlight) is converted into organic compounds via photosynthesis over a unit of time.

Gross primary productivity (GPP)

The total rate of photosynthesis in a given area; also thought of as the total amount of sun energy that plants capture and convert to glucose.

Net primary productivity (NPP)

The rate of energy storage by photosynthesizers in a given area, after subtracting the energy lost to respiration ($NPP = GPP - RL$).

Respiration loss (RL)

The energy used by plants for cellular processes like movement and internal transportation, which is lost as heat.

Productivity measurement units

Productivity is measured in units of energy per unit area per unit time, such as $kcal/m^2/yr$.

Red light absorption

In aquatic ecosystems, most red light is absorbed in the upper $1\,m$ of water.

Blue light penetration

In the clearest water, blue light can penetrate deeper than $100\,m$, affecting photosynthesis for adapted aquatic organisms.

Ecological Efficiency

The portion of incoming solar energy that is captured by plants and converted into biomass, which is approximately $1\%$ for GPP and an average of $40\%$ of that for NPP.

Factors for high NPP

Factors include water availability, higher temperature, and nutrient availability.

1st law of thermodynamics

The law stating that energy is never created or destroyed, only changed in form.

2nd law of thermodynamics

The law stating that each time energy is transferred, some of it is lost as heat, meaning useable energy decreases as it moves up a food chain.

10% Rule

An approximation that in the transfer of energy from one trophic level to the next, only about $10\%$ of the energy is passed on.

Producers

Organisms that convert the sun's light energy into chemical energy (glucose) at the lowest trophic level.

Primary Consumers

Herbivores that eat producers to obtain energy.

Secondary Consumers

Animals that eat primary consumers; these can be carnivores or omnivores.

Tertiary Consumers

Top or apex predators that eat secondary consumers.

Biomass

The mass of all living things at a specific trophic level; only about $10\%$ of the previous level's biomass can be supported by the next level.

Food chain

A model showing one linear path of energy and matter flow through an ecosystem.

Food web

A model of an interlocking pattern of food chains that depicts the flow of energy and nutrients in two or more food chains.

Trophic cascade

A ripple effect down through lower trophic levels caused by the removal or addition of a top predator.

Biogeochemical cycles

Essential cycles (such as C, N, $H_2O$, and P) that demonstrate the conservation of matter as it cycles through the environment and organisms.