The diets of Hispaniolan colubrid snakes : I. Introduction and prey genera.

Abstract

Approximately 1590 Hispaniolan colubrid snakes representing six genera and eight species were examined for prey remains (Alsophis cantherigerus, Antillophis parvifrons, Darlingtonia haetiana, Hypsirhynchus ferox, Ialtris dorsalis, Uromacer catesbyi, U. frenatus, and U. oxyrhynchus). The snakes were collected at many localities over a span of 80 years.Of 426 prey items, 77.9% were lizards (of which 69.6% were anoles), 19% frogs, 2.6% birds and mammals, and 0.5% other snakes. Darlingtonia was the only snake that did not exploit lizards; it fed exclusively on Eleutherodactylus frogs, including egg clutches. Disregarding Darlingtonia, there is no size class of Hispaniolan colubrids between 20-90 cm SVL that does not prey primarily on Anolis. Certain prey genera are added to, or deleted from, diets depending on snake size, but the data suggest that snake SVL alone does little to dictate what prey genera (or groups) are eaten. Shannon-Wiener values (H') indicate that Darlingtonia has the narrowest trophic niche, while Alsophis and Ialtris have the widest. Values of H' are not correlated with snake SVL, but highly significant (P<0.001) correlations exist between H' and mid-body circumference, head width, and snout width, and these characters may be indicators of trophic generalists and specialists. Anolis lizards are the most ubiquitous and conspicuous vertebrates on Hispaniola, and it is not surprising that they are widely exploited as a food source. Although as some snake species grow larger, anoles play a decreasingly important role in their diets, there is no evidence to suggest that they are ever abandoned as a food source by any Hispaniolan colubrid of any size.Secretive lizards of low vagility are eaten almost exclusively by wide ranging foragers (Alsophis, Antillophis); very active prey (Ameiva) is taken by sit-and-wait strategists (Hysirhynchus, U. frenatus). Those snakes which exploit the most prey groups are active foragers. Uromacer catesbyi exhibits both foraging modes, and predictably, eats diurnally active (anoles) and diurnally quiescent (hylid frogs) prey with almost equal frequency.Within Maglio's cantherigerus species assemblage, in which an Alsophis cantherigerus-like snake was ancestral to the other species, and in which longsnouted Uromacer are the most morphologically derived, there is an obvious trend toward trophic specialization on Hispaniola. The West Indies have provided an ideal natural laboratory for the investigation of many aspects of vertebrate ecology, and an arena in which to test theories of island biogeography. The most extensively studied West Indian vertebrates have been the lizards of the iguanid genus Anolis. Conversely, the ecology of West Indian snakes has been largely ignored. This is surprising in light of the fact that much has been written about Anolis predation, but little has been written about predators of Anolis; snakes may be important, frequent consumers of anoles.Hispaniola is physiographically and ecologically the most diverse of the Greater Antilles and, concomitantly, it has the most diverse snake fauna, including six colubrid genera containing 11 described species. It has rich frog and lizard faunas, but only two endemic mammals. Study of the diets of Hispaniola's colubrid snakes was undertaken to gain initial insights into the ecology of the snakes and to determine 1) what the snakes eat; 2) what relationships exist between snake diet and snake size as well as head and body proportions; 3) what relationships exist between snake foraging mode and prey type and size; 4) if anoles, as the most ubiquitous and conspicuous vertebrates on Hispaniola, comprise an important source of food; 5) if significant geographical differences in diet exist, expecially on satellite islands; 6) if "north island" and "south island" (sensu Williams 1961) Anolis ecomorphs are preyed upon by the same snake species in similar proportions; 7) if snakes are selective or opportunistic predators.This paper, the first in a series that will address all of the above topics, will briefly describe methods, snake species and prey genera. Prey genera are analyzed in terms of what snake taxa prey upon them, what size classes of snakes prey upon them, and prey genera diversity versus snake size and proportions.