The study of: the distribution and abundance of organisms, the interactions among organisms. Biotic interactions: the interactions between organisms and their non-living environments. Emergent properties become evident as we move from one level to the next higher level: organism: Energy flux and cycling of nutrients: biosphere: To understand human population growth: must consider general principles of population ecology. Study of populations in relation to the environment: a population consists of all the individuals of one kind (a single species) within a given area. Examine dynamics of groups of conspecifics: emphasize intraspecific relationships i. e. within species. The central objective of population ecology is to determine population characteristics and to follow ecological processes within populations. Age / size / sex / behavior: population. Abundance (density) / spatial distribution (dispersion) / age distribution / sex ratio / size. Development / growth / reproduction / death: population. Population growth / age distribution changes / mortality / demographics / dynamics.