Ecology and Ecosystems
Interactions in Nature
Levels of ecology
Ecology studies organisms, populations, communities, ecosystems, and the biosphere. Each level reveals different patterns of interaction and change.
Energy flow and trophic levels
Energy enters ecosystems mainly through photosynthesis and moves through food webs. Because energy is lost as heat at each transfer, higher trophic levels support fewer organisms.
Energy is not recycled
Matter cycles through ecosystems, but energy flows one way and is eventually lost as heat.
Why do food chains typically have fewer organisms at higher trophic levels?
Only a fraction of energy passes to the next trophic level; much is lost as heat and through metabolism.
Correct answer: Energy is lost between trophic transfers
What is carrying capacity?
Carrying capacity depends on resources, competition, and other limiting factors.
Correct answer: The maximum population size an environment can sustain long term.
Population growth patterns
Exponential growth
- Occurs when resources are abundant
- Produces a J-shaped curve
Logistic growth
- Slows near carrying capacity
- Produces an S-shaped curve
A species that has a large effect on community structure relative to its abundance is a:
Keystone species can strongly shape ecosystems even at low abundance.
Correct answer: Keystone species