Ecology
What you must understand
Ecology studies interactions between organisms and their environment. Energy flows through ecosystems in one direction, while matter cycles. Trophic levels form food chains/webs; only about 10% of energy transfers to the next level, so higher levels support fewer organisms.
Population ecology examines growth models: exponential (unlimited resources) and logistic (limited by carrying capacity). Community interactions include competition, predation, mutualism, commensalism, and parasitism. Succession (primary vs. secondary) describes community change over time.
Biogeochemical cycles (carbon, nitrogen, water, phosphorus) move matter through living and nonliving reservoirs. Human activity (burning fossil fuels, fertilizer runoff) alters these cycles.
Traps
- Energy flows and is lost as heat; matter cycles.
- Only ~10% of energy passes between trophic levels; the rest is lost largely as heat.
- Exponential growth assumes unlimited resources; logistic includes carrying capacity.
- Primary succession starts on bare rock; secondary succession follows a disturbance where soil remains.
Rule of thumb
For energy-transfer questions, multiply by 0.10 per trophic level.
Worked example
If producers store 10,000 kcal, primary consumers receive ~1,000 kcal, secondary consumers ~100 kcal-so top predators need large areas to feed.