Summary of Chapter Concepts

Ecological systems exist in a hierarchical organization. The hierarchy begins with individual organisms and moves up through higher levels of complexity including populations, communities, ecosystems, and the biosphere. At each of these levels, ecologists study different types of processes.

Ecological systems are governed by physical and biological principles. These principles include the conservation of matter and energy, dynamic steady states, a requirement to expend energy, and the evolution of new phenotypes and new species.

Different organisms play diverse roles in ecological systems. The major groups of organisms are plants, animals, fungi, protists, and bacteria. These organisms are involved in numerous species interactions, including competition, predation, mutualism, and commensalism. Each organism lives in specific habitats and has a particular niche.

Scientists use several approaches to studying ecology. Like all scientists, ecologists use the scientific method of developing and testing hypotheses. The testing of proximate and ultimate hypotheses can be accomplished using manipulative experiments, natural experiments, or mathematical models.

Humans influence ecological systems. The rapid growth of the human population during the past two centuries has increased human influence on ecological systems, particularly as the result of resources they consume and waste products they release.