Species Numbers, Density Compensation, and Colonizing Ability of Lizards on Islands in the Gulf of California

Abstract

The distribution of lizard species and numbers on islands in the Gulf of California was examined in light of island biogeographic theory. Using linear multiple regression techniques with the percent completeness of the island's lizard fauna as the dependent variable (LS), the relationship and predictive power of several island independent variables (in original and transformed forms) were explored. The results of this analysis differed sharply for different subsets of islands. The independent variable accounting for the most variance in LS for oceanic islands was island area; their distance from the mainland explained most of the residual variance. For land—bridge islands, maximum island elevation was the most predictive single variable, and island distance was least important. In both these island groups and considering all the islands together, island area, elevation, and the number of perennial plant species were highly correlated and explained little of each others residual variance. On 12 islands, diversity of shrub volume was also measured and was found to have less predictive power than the other variables considered. Life history attributes of each lizard species were gleaned from the literature and compared with the respective colonizing abilities of the species. In general species occurring on many Gulf islands (e.g., Uta stansburiana) may reach high mainland population densities, have potentially high birth rates and high death rates, and may be habitat generalists. Species absent from most islands and most likely to go extinct on land—bridge islands (e.g., Xantusia vigilis) have the converse of these attributes. The reasons for the divergence of these results and those expected from predictions is discussed. Lizard fauna relaxation times were calculated for land—bridge islands and were found to be inversely related to island area as predicted from island biogeographic theory. Extinction rates for lizards are about one half as high as those calculated for birds and mammals. Timed searches for lizards were also performed on most of the islands and the adjacent Baja California peninsula. These revealed that the numbers of Uta and total lizard numbers were both inversely related to the number of lizard species occupying an island. The probable reasons for such excess density compensation were examined, and it was concluded that differences in pedation intensity, insect productivity, and possibly competitive interference account for the extremely high number of lizards on some small isolated islands.

Species‐Area Relationship for Stream Fishes

“…Intensity of resource competition is likely to be low in recently colonized habitats, with densities and species richness both increasing until saturation is approached. An inverse relationship between total density and species richness, such as that observed in Panama pools, is analogous to the density compensation phenomenon previously reported for insular faunas (Case 1975). Occurrence of this phenomenon is generally associated with intense competition for resource, especially food (Case et al 1979).…”

Predicting community structure in snakes on Eastern Nearctic islands using ecological neutral theory and phylogenetic methods

“…Intrinsic factors specific to the taxa themselves, such as the ability to disperse from the mainland to islands and maintain population sizes that are resistant to extinction, may also influence species presence [3,[5][6][7][8][9][10]. Species able to disperse widely throughout the mainland and across the ocean may be better candidates for establishing populations on islands compared with those taxa that are poor dispersers or never maintain large population sizes.…”

Gradients in density variations of small rodents: the importance of latitude and snow cover

“…The numbers and total density of alternative prey species generally decreases northwards (Simpson 1964). Density compensation in the sense of Case (1975) is hardly applicable as resources generally diminish northwards and there is no evidence of such a compensation. Generalist predators should thus be least effective in regulating microtine populations in northern Fennoscandia (for long-term data on "typical microtine cycles" in northern Fennoscandia; see Tast and Kalela 1971;Lahti et al 1976;Henttonen et al 1977;Hansson 1979a;Hansson etal.…”