Chapter 20 Outline
Case Study: Toxins in Remote Places
Feeding Relationships
CONCEPT 20.1 Trophic levels describe the feeding positions of groups of organisms in ecosystems.
- Organisms can be grouped into trophic levels
- All organisms are either consumed or end up as detritus
Energy Flow among Trophic Levels
CONCEPT 20.2 The amount of energy transferred from one trophic level to the next depends on food quality and consumer abundance and physiology.
- Energy flow between trophic levels can be depicted using energy or biomass pyramids
- Energy flow between trophic levels differs among ecosystem types
- The efficiency of energy transfer varies among consumers
- Trophic efficiencies can influence population dynamics
Trophic Cascades
CONCEPT 20.3 Changes in the abundances of organisms at one trophic level can influence energy flow at multiple trophic levels.
- Trophic interactions can trickle down through multiple trophic levels
- What determines the number of trophic levels?
Food Webs
CONCEPT 20.4 Food webs are conceptual models of the trophic interactions of organisms in an ecosystem.
- Food webs are complex
- The strengths of trophic interactions are variable
- Some species are more important in food webs than their numbers would indicate
- Direct and indirect effects determine net interaction strength
- Does complexity enhance stability in food webs?
Case Study Revisited: Toxins in Remote Places
Connections in Nature: Biological Transport of Pollutants
