Ecology
Core concepts
Ecology studies interactions at organism, population, community, ecosystem, and biosphere levels. Populations grow exponentially under unlimited resources; logistic growth adds carrying capacity (K). Density-dependent factors (competition, disease, predation) intensify with crowding; density-independent factors (weather, fire) do not. Species interactions include competition, predation, parasitism, mutualism, and commensalism. In food webs, energy flows from producers to consumers and is lost as heat; typically only about 10% passes to the next trophic level. Biogeochemical cycles (carbon, nitrogen, phosphorus, water) recycle matter. Ecological succession may be primary (bare substrate) or secondary (disturbed but soil present). Biodiversity supports ecosystem services such as pollination, water purification, and climate regulation; human activities can reduce biodiversity and alter cycles.
Traps
Energy pyramids always taper; biomass and numbers pyramids may not. The 10% rule applies to energy transfer, not total energy. Primary succession starts without soil; secondary starts after a disturbance leaves soil. A niche is a species’ role; habitat is where it lives.
Worked example
If producers capture 10,000 kcal, herbivores receive about 1,000 kcal, secondary consumers about 100 kcal, and tertiary consumers about 10 kcal. Rule of thumb: multiply by 0.10 each trophic step.