Part 3 Communities and Ecosystems In nature, areas of land and volumes of water contain assemblages of different species, in different proportions and doing different things. These communities of organisms have properties that are the sum of the properties of the individual denizens plus their interactions. | Introduction In nature areas of land and volumes of water contain assemblages of different species in different proportions and doing different things. These communities of organisms have properties that are the sum of the properties of the individual denizens plus their interactions. The interactions are what make the community more than the sum of its parts. Just as it is a reasonable aim for a physiologist to study the behavior of different sorts of cells and tissues and then attempt to use a knowledge of their interactions to explain the behavior of a whole organism so ecologists may use their knowledge of interactions between organisms in an attempt to explain the behavior and structure of a whole community. Community ecology then is the study of patterns in the structure and behavior of multispecies assemblages. Ecosystem ecology on the other hand is concerned with the structure and behavior of the same systems but with a focus on the flux of energy and matter. We consider first the nature of the community. Community ecologists are interested in how groupings of species are distributed and the ways these groupings can be influenced by both abiotic and biotic environmental factors. In Chapter 16 we start by explaining how the structure of communities can be measured and described before focusing on patterns in community structure in space in time and finally in a more complex but more realistic spatiotemporal setting. Communities like all biological entities require matter for their construction and energy for their activities. We examine the ways in which arrays of feeders and their food bind the inhabitants of a community into a web of interacting elements through which energy Chapter 17 and matter Chapter 18 are moved. This ecosystem approach involves primary producers decomposers and detritivores a pool of dead organic matter herbivores carnivores and parasites plus the physicochemical environment that provides living conditions and acts both as a source .
