Introduction

Methods

Results

Conclusions

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Many higher taxa exhibit latitudinal gradients in species richness, geographic range size, and body size. However, potentially interdependent relationships between body size, range area, and continental area mean that examination of a single univariate or bivariate pattern is unlikely to be of great utility when asking questions about latitudinal gradients. Therefore, I examined interactions between multiple variables, largely focusing on mechanisms structuring geographic ranges of 144 species of New World venomous snakes [families Elapidae (coral snakes) and Viperidae (pitvipers)]. These two lineages are monophyletic, collectively span 99º of latitude, and are extremely variable in body size and geographic range sizes.

Data were gleaned from a variety of primary and secondary sources. Island endemics and poorly-known species were discarded from the data set, resulting in a solely continental assemblage with reasonably well-known geographic range areas. The maximal known body length for each species was used as a relative indicator of body size. My measure of geographic range area corresponded to the extent of occurrence of each species, using a grid-cell tallying method. I calculated the width (km) of continental landmasses in 2.5º increments. Because phylogeny may confound macroecological studies, I used network autocorrelation to calculate the effects of shared evolutionary history on variation in geographic range area and body size within each family, using phylogenies constructed from multiple sources.

Results

Conclusions

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