© 2002 Blackwell Science Ltd. http://www.blackwell-science.com/geb RESEARCH LETTER Global Ecology & Biogeography (2002) 11, 41–47 Blackwell Science, Ltd Does body size predict dates of species description among North American and Australian reptiles and amphibians? ROBERT N. REED* and SCOTT M. BOBACK Department of Biological Sciences, Auburn University, Auburn AL 36849–5414 U.S.A. ABSTRACT Which factors determine whether a species is obvious to collectors? For some taxa, species of small body size tend to be described later than large-bodied species, perhaps because large animals are more obvious or easily captured. Thus it has been proposed that current estimates of species numbers within taxa may be biased, as they may not include small species. However, the trend for recently described species to be small-bodied has only been observed in a few higher taxa, and may not be general. Herein, we examine the relationships between body size and date of description for the entire herpeto- faunas of North America and Australia (snakes, lizards, turtles, frogs and salamanders). We found that body size is generally a poor predictor of description date in herpetofaunal taxa. Even for most taxa that did exhibit a negative relationship between these variables, recently described species could not be dis- tinguished from a random draw from overall species pools. We interpret our results in the light of the history of exploration of these continents and the biology of reptiles and amphibians. Key words Amphibians, Australia, body size, date of description, macroecology, North America, randomiza- tion, reptiles, species richness estimates. INTRODUCTION Within a variety of higher taxa, the probability of describing a species tends to be related to body size (Diamond, 1985; Gaston, 1991; Gaston & Blackburn, 1994; Gaston et al., 1995). In other words, large fierce animals may be rare (Colinvaux, 1980) but large animals do tend to be collected and described earlier than small animals. Our knowledge of faunal diversity both within and among taxa may thus be biased in favour of large species, especially in incompletely surveyed areas such as the tropics. If this bias exists, estimates of species numbers and concomitant conservation planning should be adjusted to account for small and as yet undescribed species within each taxon. The explanatory power of body size in predicting descrip- tion dates varies widely among taxa, and has only been examined in some insects, birds and mammals (Gaston, 1991; Gaston & Blackburn, 1994; Patterson, 1994; Blackburn & Gaston, 1995; Gaston et al., 1995). The best evidence for a strong relationship comes from insects, but even among insect taxa this evidence is far from uniform (Gaston, 1991; Gaston et al., 1995). Among South American birds, geo- graphical range size and relative abundance are the best predictors of description date, while body mass is a very poor predictor of description date (Blackburn & Gaston, 1995). Clearly, the assumption that recently described species are small is debatable and further data are needed to assess the generality of this hypothesis. In this paper we examine relationships between body size and description date for the reptiles and amphibians of North America and Australia. We first use Spearman cor- relations to test for negative relationships between these variables. Secondly, we examine possible confounding effects of the shape of body size distributions on regression results via randomization tests. Finally, we test the generality of the body size/description date thesis by examination of patterns across higher taxa and between the two continents. MATERIALS AND METHODS Our dataset included 1433 species from five higher taxa: lizards, snakes, turtles, frogs, and salamanders, encompassing the entire non-marine herpetofaunas of Australia and North America (exclusive of Mexico). Dates of description were taken from Cogger (2000) for Australian species and Collins (1997) for North American species. Some taxonomic deci- sions in the latter publication are under debate (Frost et al., * Corresponding author and current address: Robert N. Reed, Drawer E, Savannah River Ecology Laboratory, Aiken, SC 29802, USA. E-mail: reed@srel.edu