MSc Project: Macroecology of Lizards in North America
Co-advisors: Shai Meiri & Ian Owens.
The macroecological patterns of three groups of terrestrial vertebrates – amphibians, birds and mammals – have been studied in great detail at both regional and global scales. In this study, I explore macroecological patterns in the fourth major group of terrestrial vertebrates, the reptiles. I focus particularly on the geographical distribution fo species richness, endemism, range size and body size of the lizards of North America.
I digitized range maps of 139 lizard species and collected ecological data for 119 species from the published literature. Based on this GIS database I found that lizard species richness is relatively high in Baja California and southwest USA, and geographical patterns of richness are strongly correlated to the maximum temperature and radiation. Endemic species richness does not follow the same pattern as overall species richness, with most endemic species being found in Baja California, and some others in Florida. In agreement with the findings of studies on other terrestrial vertebrates, geographical range size decreases of lizards with latitude, and large-bodied species tend to reach further north than small-bodied species. However, contrary to the patterns found in some other terrestrial groups, there was no correlation between lizard range size and body size. I also found that chiefly herbivorous lizard species have larger body sizes than carnivorous species, and even within a single family, Phrynosomatidae, species with strictly carnivorous diet are smaller than chiefly carnivrous species and omnivorous species are the largest of all. When I looked at the influence of activity patterns on macroecology I found that nocturnal species are all in the Gekkodnidae family, and they all have relatively small body size and small range size. This family is restricted in low latitude areas and the unusual patterns illustrate the broader finding that species body size varies significantly with phylogeny in this group of organisms.
I also qualitatively compared the macroecological patterns of lizards in North America with those of the other three groups of terrestrial vertebrates and found that patterns in the other terrestrial vertebrate groups are not always predictive in those of lizards. Patterns in lizard species richness are very different from those of amphibians in North America, but are similar to those of mammals and birds. Range sizes of birds and mammals are larger than that of lizards, and amphibians have even smaller range size. Taken together, therefore, my results suggest that although several aspects of lizard macroecology are rather similar that of other terrestrial vertebrates, there are also some intriguing differences. I interpret these in the light of the fact that reptiles are ectothemic and typically have a stronger reliance on their thermal environment than either mammals or birds.
