Learning Objectives

21.1.1 Describe how energy flow among trophic levels in an ecosystem is related to the food selection of consumers.

21.1.2 Explain how both primary production and detritus can be at the base of food chains.

21.1.3 Evaluate how terrestrial detrital energy inputs from outside an ecosystem (allochthonous) would change in a river from its source to where it reaches the ocean.

In Chapter 20, we introduced Ray Lindeman's simplified approach to categorizing groups of organisms in an ecosystem according to how they obtain energy (see Figure 20.3). Rather than grouping them by their taxonomic identity, he grouped them into categories based on how they obtained energy in the ecosystem. In this section, we'll take a closer look at these feeding categories.