Ecology
Ecology tests organism-environment relationships, population growth, species interactions and adaptations.
Core rules
- Population density is numbers per unit area or volume; natality, mortality, immigration and emigration change it.
- Exponential growth occurs under unlimited resources; logistic growth shows carrying capacity and an S-shaped curve.
- Interactions include mutualism, commensalism, parasitism, predation and competition.
- Gause's competitive exclusion principle states that two species cannot occupy the same niche indefinitely.
- r-selected species have many small offspring with little care; K-selected species have fewer offspring with more care.
Worked example
In mark-recapture, 100 fish are marked and released. Later, 200 are caught and 20 are marked. Estimated population N = (marked first x total second) / marked recaptures = (100 x 200) / 20 = 1,000. The reasoning assumes marked and unmarked fish mix randomly and are equally likely to be recaptured; violation of these assumptions biases the estimate.
Traps
- Commensalism benefits one species and leaves the other unaffected.
- Parasitism does not always kill the host immediately.
- Exponential growth assumes unlimited resources and cannot continue forever.
- A niche is not just habitat; it includes functional role and resource use.