Ecology and Environmental Biology
What this domain tests
Ecology and Environmental Biology covers population dynamics, species interactions, energy flow, nutrient cycling, succession, and conservation. Questions often use graphs, life tables, or field estimates to test whether you can distinguish pattern from mechanism.
Core rules and concepts
- Population growth: exponential dN/dt = rN; logistic dN/dt = rN(1−N/K).
- Mark–recapture estimate: N ≈ (M × C)/R, where M is marked initially, C captured second, R marked recaptures.
- Energy transfer between trophic levels is about 10% efficient; most is lost as heat.
- Gross primary productivity (GPP) minus respiration = net primary productivity (NPP).
- Density-dependent factors such as competition and disease intensify with population size; density-independent factors such as fire and storm do not.
- Succession: primary starts on bare substrate; secondary follows disturbance with soil intact.
Worked example
Researchers mark 40 fish, release them, then capture 50 fish and find 10 marked. Estimate population size: N ≈ (40 × 50)/10 = 200. Reasoning: assume marked and unmarked fish mix randomly and have equal capture probability. If marked fish avoid traps, the estimate is biased upward; if they are more catchable, it is biased downward.
Traps that cost marks
Do not confuse GPP with NPP. Do not treat the 10% rule as exact for all ecosystems. Do not call a density-independent factor density-dependent just because it kills many individuals. Do not assume a high biodiversity index always means high ecosystem function; context matters. In mark–recapture, do not forget that the second sample includes both marked and unmarked individuals.