Ecology and Interdependence of Life
What this domain tests
Ecology and Interdependence of Life examines relationships among organisms and their environments. Expect energy flow, trophic levels, food webs, biogeochemical cycles, population growth, carrying capacity, symbiosis, succession, biodiversity, and human effects on ecosystems. You should trace consequences through a food web and distinguish matter cycling from energy flow.
Core rules
- Producers capture energy; consumers transfer it; decomposers recycle matter.
- Energy flows one way and is lost as heat at each trophic level; roughly 10% is transferred between levels.
- Matter such as carbon, nitrogen, and water cycles through living and nonliving reservoirs.
- Population size is limited by density-dependent factors (competition, disease) and density-independent factors (fire, drought).
- Carrying capacity is the maximum population an environment can sustain.
- Symbiosis includes mutualism, commensalism, and parasitism.
Worked example
A food chain has 10,000 kcal of energy in producers, 1,000 kcal in primary consumers, and 100 kcal in secondary consumers. Estimate the energy available to a tertiary consumer. Reasoning: Apply the 10% rule between trophic levels. Secondary consumers hold 100 kcal, so the tertiary consumer receives about 10% of that, or 10 kcal. The missing energy is used in metabolism, lost as heat, or passed as waste. The answer should not imply that energy is recycled; matter cycles, but energy dissipates.
Traps
- Reversing the arrows in a food web; arrows show energy flow to the consumer.
- Saying energy is recycled; matter cycles, energy flows.
- Treating the 10% rule as exact rather than an estimate.
- Confusing a population with a community.