Ecology and Environmental Science
Domain 5 - Ecology and Environmental Science
This domain tests population dynamics, species interactions, energy and nutrient flow, succession, and human effects on ecosystems.
Populations and communities
- Exponential growth (r) is unlimited; logistic growth adds carrying capacity K, producing an S-curve with density-dependent limits (food, disease, space). Density-independent factors include weather and fire.
- Survivorship curves: Type I (late loss, humans), Type II (constant, birds), Type III (early loss, many fish and plants).
- Interactions: competition (competitive exclusion; resource partitioning allows coexistence), predation (including keystone effects), mutualism (+/+), commensalism (+/0), parasitism (+/−).
- Age-structure diagrams predict growth: a broad base indicates an expanding population, a narrow base a declining one.
Ecosystems
Energy flows one way and is lost as heat; roughly 10% transfers between trophic levels, so food chains rarely exceed four or five links. Gross primary productivity minus respiration equals net primary productivity. Biogeochemical cycles: carbon (photosynthesis, respiration, combustion, dissolution), nitrogen (fixation, nitrification, assimilation, denitrification - atmospheric N₂ is unusable to most organisms), phosphorus (sedimentary, no gas phase, often limiting). Primary succession begins on bare substrate (lichens, mosses); secondary succession follows disturbance with soil intact.
Worked example
A lake is sampled by mark–recapture: 50 fish are captured, marked, released, and mixed. A second sample of 120 contains 15 marked fish. Estimated population N = (marked in first sample × total in second sample) ÷ marked in second sample = (50 × 120) ÷ 15 = 400. The estimate assumes a closed population, no mark loss or mortality, thorough mixing, and equal catchability; if marked fish become trap-shy, the estimate is biased upward.
Traps
Confusing exponential with logistic growth; calling a density-dependent factor density-independent; reversing the 10% rule (energy is lost, not gained); assuming nitrogen gas is directly usable; mixing up primary and secondary succession; forgetting that habitat loss and invasive species, not pollution alone, are leading causes of biodiversity decline; treating a population estimate as a census.