19: Food Webs

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Page ID: 84662

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Learning Objectives

Differentiate among the components of food webs, the sources of energy to food webs, and the types of food webs
Use quantifiable characteristics to describe and compare food webs
Appreciate the key ecosystem role that apex predators play through trophic cascades

Summary

The food webs of all ecosystems have autotrophs at the base; these producers may fix carbon using energy from the sun (photoautotrophs) or from specific chemical compounds (chemoautotrophs). The energy produced at the base of the food web moves through several levels of heterotrophs, including detritivores, herbivores, omnivores, and carnivores, but some of this energy is lost during each transfer up the food web. When the apex predator or keystone predator of an ecosystem is removed, this can result in a trophic cascade that impacts the entire food web. Food webs are extremely complex, and cannot be easily depicted on paper, so the food webs we see are simplifications of reality; the simplest form is a food chain, which involved a linear sequence of interactions from primary producer to apex predator. Scientists quantify food webs by calculating transfer efficiency, food web length, and food web connectance.