Fuzzy competitive exclusion explains parapatric distributions and highlights areas of concern for native species due to biological invasions

Abstract

The application of the fuzzy concepts of favorability (the degree to which environmental conditions are propitious for the occurrence of individual species) and favorableness (the degree to which environmental conditions are simultaneously favorable for competing species) operationalize a fuzzy version of the competitive exclusion principle that may be applied at biogeographic scales. Favorability was obtained by performing species distribution models applying favorability functions, while favorableness was derived from the application of the fuzzy intersection between the favorability for competing species. Potentially competing species would coexist in high-favorableness locations, as the demands of all species would be well fulfilled. In locations of low favorableness, the result would be either autecological exclusion of species or autecological segregation, as abiotic conditions are unfavorable for at least one of the species. Competitive exclusion would occur at the intermediate stretch of the favorableness gradient, as the conditions would be good enough for persistence of each species separately but not enough for permanent coexistence. After plotting individual favorability values along the gradient of favorableness for potentially competing species of turtles, deer, hares and vipers, the pairs of species and the specific geographical areas affected by competitive exclusion were identified. Among native species (hares and vipers) this resulted in parapatric distributions. In the case of native and introduced species (turtles and deer) this may be used to identify the particular areas where the native species are threatened of exclusion by the introduced species. This is important both theoretically and for biodiversity conservation planning.