Ratio of Basal to Top Species

Finally, ratios of species and links from basal to intermediate to top trophic levels (where basal species are prey only, intermediate species are prey and predators, and top predators have no predators) are expected to be constant (Briand and Cohen 1984). This implies a large proportion of top predators. Top predators are expected to comprise 29% of all species in a given community, and prey-to-predator ratios should be < 1.0 (Briand and Cohen 1984).

As shown for the properties discussed in the preceding text, this property reflects poor resolution of arthropod diversity. Top predators appear to be common because they are easily distinguished vertebrate species, whereas poor taxonomic resolution at basal and intermediate levels underrepresents their diversity. Reagan et al. (1996) reported that in a rainforest food web, which distinguished "kinds" of arthropods, representation of basal and intermediate species was 30% and 70% of all species, respectively, and the proportion of top predators was < 1%. Polis (1991b) also reported that top predators were rare or absent in desert communities. Both Polis (1991b) and Reagan et al. (1996) reported that ratios of prey species to predator species are much greater than 1.0 when the true diversity of lower trophic levels is represented.

Although the properties of food webs identified by early theorists may be flawed to the extent that arthropod diversity has not been resolved adequately, they represent hypotheses that have stimulated considerable research into community organization. Future advances in food web theory will reflect efforts to address arthropods at the same level of taxonomic resolution as other taxa.

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