Energy Flow in Ecosystems

Energy flows through an ecosystem in a one-way stream, from primary producers to various consumers. A food chain is a series of steps in which organisms transfer energy by eating and being eaten.

Ecologists call this network of feeding interactions a food web

Detritus Pathway: decomposers convert that dead material  detritus (broken down into nutrients) eaten by detritivores, such as crayfish, grass shrimp, and worms.

Food Webs and Disturbance Remove/affect one part  cascading effect (changes in feeding relationships)

Trophic Levels and Ecological Pyramids Pyramids of energy show the relative amount of energy available at each trophic level. Each step in a food chain or food web is called a trophic level. T5 T4 T3 T2 T1

Pyramids of Energy 10% of the energy available within one trophic level is transferred to the next trophic level. 90% Lost: waste, heat, cell respiration

Trophic Levels and Ecological Pyramids Total amount of living tissue within a given trophic level is called its biomass. Shows the relative amount of living organic matter at each trophic level.

Trophic Levels and Ecological Pyramids A pyramid of numbers shows the relative number of individual organisms at each trophic level in an ecosystem.

Implications What does it mean to “eat low on the food chain”? How can we feed more people? How much space and energy does it take to produce a field of corn for consumption versus raising cattle for consumption?