2 - Defining and measuring versatility

Summary

An ecologist's judgement of the ecological versatility of a species is very much a filtered one. The most important filters are the ecological characteristics of the taxa under study, and the taxonomically inspired biases of investigators. For example, one reads of specialized and generalized insectivores (e.g., Freeman 1979), but surely this can only mean a relative degree of versatility nested within a coarser degree of food specialization or generalization? The biases of the investigator, engendered by the characteristics of the taxon that she or he studies, often lead to this type of loose terminology.

However, this is by no means the only source of inexactness. Ecological scale – the spatial and temporal scales at which organisms operate – also alters the perspectives of how specialized or generalized species are (Allen and Starr 1982, Dayton and Tegner 1984, Wiens et al. 1987, Orians and Wittenberger 1991, Levin 1992). This works in two ways, one organismal and one investigator-based. Many workers have noted that different organisms show different levels of discrimination, and hence, dissimilar responsiveness to spatial variation in resource availabilities (e.g., Addicott et al 1987, Pahl-Wostl 1993). This often leads to an altered perception of the ecological versatility of the population or species over different spatial scales. The often-cited review of Fox and Morrow (1981) showed how the level of perceived specialization of a species depends upon how many populations are considered. Populations of a species may show high resource specificity locally, but shift to, and specialize on, alternative resources elsewhere (e.g., Nitao et al. 1991). Therefore, the species as a whole actually displays greater generalization at a large scale than do its local populations.