Ecology

Seven topics on how organisms interact with each other and their environment. Responses to the environment and why behavior — innate, learned, and signaling — is heritable and shaped by natural selection, the energy flow through ecosystems where energy moves one way and is lost as heat so only about 10% reaches the next trophic level, population ecology where growth shifts from exponential to logistic as resources run short, the effect of density on populations and the split between density-dependent and density-independent factors, community ecology of predator-prey cycles, symbiosis, and competition softened by niche partitioning, biodiversity as more than a species count — genetic, species, and ecosystem diversity — and the disruptions that ripple through whole webs when keystone species are lost or invasive species arrive.