Ecology and Environment
Ecology and Environment
This domain tests populations, communities, ecosystems, and human effects on them. Expect data interpretation, energy-flow calculations, and questions about sampling and succession.
Core rules
- Population size changes through births, deaths, immigration, and emigration. Exponential growth occurs with unlimited resources; logistic growth levels off at carrying capacity (K).
- Energy is lost at each trophic level, commonly about 90%, so food chains are short and top predators are few.
- Nutrient cycles differ from energy flow: energy passes through and is lost as heat, while carbon, nitrogen, and phosphorus are recycled.
- Primary succession starts on bare substrate; secondary succession follows disturbance where soil remains.
- Biodiversity includes species richness and evenness; it is measured with quadrats and transects for plants and mark–recapture for mobile animals.
Worked example
A mark–recapture study marks 40 animals, then recaptures 50, of which 8 are marked. Estimate N = (marked × recaptured) / marked in recapture = (40 × 50) / 8 = 250. Reasoning: the marked proportion in the second sample is assumed to represent the whole population. This requires a closed population, no mark loss, and equal catchability.
Traps
- Net primary productivity is gross productivity minus respiration.
- Mark–recapture assumes no immigration, emigration, births, or deaths between samples.
- A high number of species does not always mean high evenness; one dominant species can lower diversity.
- Energy pyramids are always upright, but numbers and biomass pyramids can be inverted.