Ecology and the Environment
What to know
Ecology covers population dynamics, community interactions, energy flow, nutrient cycling, and human environmental impacts. Know population growth models (exponential vs. logistic with carrying capacity), factors that limit populations (density-dependent and density-independent), and survivorship patterns. Understand community interactions: competition, predation, mutualism, commensalism, parasitism. Know food chains and webs, trophic levels, and the 10% energy transfer rule. Understand the carbon, nitrogen, and water cycles and the roles of producers, consumers, and decomposers. Recognize ecological succession (primary vs. secondary) and biodiversity's role in ecosystem stability. Human impacts include pollution, habitat loss, invasive species, and climate change.
Traps
Questions often test the 10% rule and ask how much energy reaches a top predator. Another trap is confusing density-dependent (food, disease) with density-independent (weather, fire) factors. Watch for questions about primary versus secondary succession: primary starts on bare rock with no soil; secondary follows a disturbance where soil remains. Also avoid the misconception that energy cycles; matter cycles, but energy flows and is lost as heat.
Worked example
If producers capture 10,000 units of energy, the primary consumers receive about 1,000, secondary consumers about 100, and tertiary consumers about 10. Rule of thumb: each trophic level retains roughly 10% of the energy from the level below, so food chains are short.
Rule of thumb
Matter cycles through ecosystems; energy flows one way and is dissipated as heat.