This document discusses key concepts around biodiversity and population ecology. It defines biodiversity as the variety of living organisms within an environment. Biodiversity is important as it sustains the flow of energy through food webs. Species provide direct economic value through resources like food and medicine, and indirect economic value through ecosystem services. A population's size is determined by its natality and mortality rates. Population growth is limited by density-independent factors like disasters and density-dependent factors like competition for resources when the population reaches the carrying capacity.