Various activities of organisms like population explosion, availability and shortage of food, and overcrowding result in shifts in the ecosystem. These shifts further result in different kinds of succession. Succession is the step by step orderly and gradual replacement of communities that lead to a climax community. At the end of this course, among other things, students will gain very good understanding of climax communities, primary succession, causes, effects and adaptations to overcrowding, causes and effects of food shortage, balance in nature, dynamic equilibrium in ecosystems and methods of controlling human population.