Ecology: Energy Flow, Trophic Levels, and Food Webs

Energy

The ability to do work or the process of doing work.

Potential energy

Stored energy, usually energy stored in complex organic molecules.

Kinetic Energy

Energy being used or released, including movement of mass, light, heat, solar radiation, and other forms.

First Law of Thermodynamics

Energy cannot be created nor destroyed; account for the energy on both sides of the transformation.

Second Law of Thermodynamics

No transformation is 100% efficient; without the addition of energy, disorder in a system increases.

Trophic Level

A level in a food chain or food web, representing the flow of energy through populations.

Producer

An autotroph, typically a green plant, that produces energy through photosynthesis.

Primary Consumer

A heterotroph, specifically a herbivore, that consumes producers.

Secondary Consumer

A heterotroph, specifically a carnivore, that consumes primary consumers.

Third Level Consumer

A heterotroph, specifically a carnivore, that consumes secondary consumers.

Food Chains

Describes the flow of energy through the populations in a community.

Food Webs

Shows all possible transfers of energy in a community.

Apex predator

The predator not eaten by others in the food web.

Pyramid of biomass

Illustrates the amount of biomass at each trophic level, following the 10% rule.

Pyramid of energy

A necessary consequence of the Second Law of Thermodynamics, showing energy loss at each trophic level.

Pyramid of size

Indicates that animals at higher trophic levels tend to be larger than their prey.

Pyramid of numbers

Shows that animals at higher trophic levels tend to be fewer than their prey.

Gross Primary Productivity (GPP)

Mass of carbon fixed through photosynthesis.

Net Primary Productivity (NPP)

Mass of carbon fixed through photosynthesis minus that emitted by plants during respiration.

Factors that influence productivity

Moisture, temperature and seasonality, and disturbance.

Top Down vs. Bottom Up Control

Herbivores may limit the growth of plants, reducing productivity; carnivores may limit herbivore populations, increasing plant growth.