A simplified food web
Food webs are a graphical depiction of the interconnections among species based on feeding relationships.
Food webs are a graphical depiction of the interconnections among species based on feeding relationships, and are a core concept of the field. The role of keystone species in communities is another important tenet, and one of the best–known ideas in community ecology. Keystone species are those whose
presence or absence profoundly affects other species in the community, disproportionately to its abundance (relative representation of species).
Community ecologists not only study the structure of communities but also changes in that structure. What do volcanoes, glaciers, sand dunes, storms,
agriculture, and fire have in common? They all initiate the process of change in communities.
In the adjacent figure, illustrating a three trophic food chain (producers–herbivores–carnivores) linked to decomposers. A food web is a set of interconnected food chains by which energy and materials circulate within an ecosystem. The movement of mineral nutrients is cyclic, whereas the movement of energy is unidirectional and noncyclic. Trophic species are encircled as nodes and arrows depict the links.
In this chapter, we will examine the factors that are most significant in structuring a community – in determining how many species there are overall, which particular species are present, and the relative abundance of these species. We begin with a fundamental factor influencing community structure: the interactions between the organisms in a community.