Patterns Of Community Structure

A central theme of community ecology has been identification of patterns in community structure across environmental gradients in space and time (see also Chapter 10). The diversity of community types at landscape and regional scales has been a largely neglected aspect of biodiversity but is important to the maintenance of regional species pools and metapopulation dynamics for many species. In addition, the mosaic of community types on a landscape may confer conditional stability to the broader ecosystem, in terms of relatively consistent proportions of community types over time (see Chapters 10 and 15).

Identification of patterns in community organization has become increasingly important to population and ecosystem management goals. Introduction of exotic insects to combat noxious pests (weeds or other insects) requires attention to the ability of the biocontrol agent to establish itself within the community and to its potential effects on nontarget components of the community. Efforts to conserve or restore threatened species require consideration and maintenance of the underlying community organization.

Depending on the descriptive approach taken (see earlier in this chapter), patterns have been sought in terms of species diversity, food web structure, or guild or functional group composition. Unfortunately, comparison of data among communities has been hampered by the different approaches used to describe communities compounded by the variety of sampling techniques, with their distinct biases, used to collect community data. For example, sweep netting, light trapping, interception trapping, pitfall trapping, soil coring, canopy fumigation, and branch bagging are among the techniques commonly used to sample terrestrial arthropods (Leather 2005). These techniques differ in their representation of nocturnal versus diurnal flying insects, arboreal versus soil/litter species, and sessile versus mobile species, etc. (e.g., Blanton 1990, Leather 2005, Majer and Recher 1988, Southwood 1978). Relatively few studies have used the same, or similar, techniques to provide comparative data among community types or locations. Some proposed patterns have been challenged as subsequent studies provided more directly comparable data or increased resolution of arthropod taxonomy (e.g., Hawkins and MacMahon 1989, Polis 1991b, Reagan et al. 1996). Disturbance history, or stage of postdisturbance recovery, also affects community structure (e.g., Harding et al. 1998, Schowalter et al. 2003, E. Wilson 1969; see Chapter 10). However, the history of disturbance at sampled sites often is unknown, potentially confounding interpretation of differences in community structure. Nevertheless, apparent patterns identified at a variety of spatial scales may serve as useful hypotheses to guide future studies.

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