19.4 Populations

Population (one species, same area, same time), community (all populations together), ecosystem (community + non-living environment) — three terms that NEST. Sigmoid growth curve with four phases (lag, log/exponential, stationary, death) and four limiting factors (food supply, competition, predation, disease) that produce the characteristic S-shape. HL extension: explaining each phase mechanistically — lag = adapting + few breeders, log = no limits yet, stationary = limiting factors balance growth (birth = death at carrying capacity), death = limiting factors overwhelm.