This is a second in a series of 3 PowerPoint presentations on Ecology. This presentation includes 34 slides. There is a discussion of organization of ecosystem basics (species, population, community, ecosystems, habitat, niche, etc.). It also covers species interactions (predator-prey, competition, and symbiotic relationships of parasitism, commensalism, and mutualism). Factors that determine population size are covered. There are also discussions on primary and secondary succession.