Food Web Connectance

Community connectance, the proportion of potential feeding relationships that actually occur in the community (Pimm 1982), should increase with increasing species richness as follows:

where L is the number of links and S is the number of species (Martinez 1992). This constant connectivity hypothesis predicts that, on average, each species will be involved in predator-prey interactions with 14% of the other species in the community. Havens (1992) analyzed 50 pelagic food webs with species richness ranging from 10-74 and found that the number of links per species increased 4-fold over this range. Reagan et al. (1996) reported that the food web in a tropical forest in Puerto Rico supported constant connectance at low taxonomic resolution but that connectance dropped quickly as taxonomic resolution was increased. Polis (1991b) and Reagan et al. (1996) also found that the prediction that each species interacts with only 2-5 other species greatly underestimates the actual number of linkages per species and concluded that these properties are sensitive to taxonomic resolution.

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