Chapter 19: Community Ecology
Larry B. Crowder
A “community” is often defined as a group of populations that occur in a common area and that interact with one another. Many ecologists prefer the term “assemblage” to define a group of co-occurring populations, a term that does not imply significant interactions among populations. In this paper, I often use the more common term “community” but do not intend it to mean that all communities must be highly interactive. Community ecology is a young science and its applications to fisheries are even more recent. As a result, there are few “standard methods” in fish community ecology. However, a community-oriented approach to fisheries biology is becoming increasingly necessary (Steele et al. 1980; May 1984b). Practical experience has shown that a particular fish population often cannot be studied and understood, much less managed, in isolation from other populations with which it interacts.
Many of the ideas and theories elaborated by community ecologists apply directly to fishes, but others do not. Most of the theory in community ecology derives from work with birds and mammals, which tend to have fairly predictable growth rates and for which the juveniles are similar in size to the adults. In strong contrast, fish growth rates can be highly variable, and fish can increase several orders of magnitude in size during their lifetimes. This often results in complex interactions among populations that are difficult to characterize. But we need to understand how ecological roles of fishes shift during ontogeny in order to manage multispecies fisheries (May 1984b).
In this chapter, I outline the major philosophical approaches to fish community ecology and give examples of how each can help us understand the structure and dynamics of fish communities. Competition, predation, and symbiotic interactions are important factors that structure fish communities, as are historical and stochastic factors. For each interaction, I review cases illustrating different approaches. Ultimately, the diversity of species occupying a particular system may be related to species interactions, although biogeographic factors will also be important.