Distribution of Maximum Snout-Vent Length among Species of Scincid Lizards

Abstract

-The distribution of maximum snout-vent length for 1206 of the approximately 1227 described species of scincid lizards ranges from 23-490 mm, has a mode of 55 mm, a median of 69 mm, a mean of 82 mm, and is strongly right skewed. At both the small and large ends of the distribution, there are noticeable lineage effects, that is, a few lineages contribute a large proportion of the species. Perhaps surprisingly given the surface-volume relationships of small animals, many of the smallest species occur in arid or seasonally arid habitats. Egg size may be the limiting factor in the evolution of small adult size. The larger species tend to be burrowers (litter and sand swimmers), have diets different from the usual (for scincids) arthropods, occur on small oceanic islands (absence of predators?), or are live-bearing. Species of skinks that have gone extinct in the last 200 years have been relatively larger than species that have survived. The overall shape of the size distributions for scincids and gekkonids, the only other major group for which there are comparable data, are surprisingly similar, suggesting a common cause such as tracking evolutionarily the same size spectrum of arthropod prey. al of Herpet logy, Vol. 35, No. 3, pp. 383-395, 2001 right 2 01 Society for the Study of Amphibi s and R ptiles ibution of Maximum Snout-Vent Length among Species of Size is a key feature in the biology of most animals because of its relationship to a wide variety of ecological and physiological attributes (Peters, 1983; Calder, 1984; Schmidt-Nielsen, 1984; Harvey and Pagel, 1991). But what determines size? One approach to this question is to examine the distribution pattern of some measure of size both within and among lineages. Here I present the distribution curve for one aspect of size, maximum snout-vent length, for the largest family of lizards, the skinks; make some observations about its shape and some attributes of the species at its extremes (where correlating factors are likely to be most pronounced), and compare it with the only other large group of lizards for which there are similar data, the geckos. There are approximately 1227 described species of living and recently extinct (since Euroe is a key feature in the biology of most i als because of its relationship to a wide vai ty of ecol gical nd physiological attributes pean expansion) scincid lizards (pers. obs.). These species comprise approximately 31.7% of all lizard species (based on a total of 3865 species, Bauer, 1992). Skinks are also one of the most diverse lizard groups, in part, because of their repeated reduction of limbs and their consequent extension into subsurface microhabitats. Data on size for 1206 species of skinks (98.3% of all skink species) form the basis of this analysis. MATERIALS AND METHODS Maximum snout-vent length (SVL and henceforth, size), measured to the nearest whole millimeter, was the variable chosen to estimate species size. There were two reasons for choosing this variable. First, it is easy to determine, especially from the literature, and, hence, it can be broadly surveyed. Second, it is indicative of the 383 This content downloaded from 157.55.39.35 on Wed, 31 Aug 2016 04:37:28 UTC All use subject to http://about.jstor.org/terms