Long-term comparison of diets in three syntopic rattlesnake species

Pawlicki, Anthony

pawlicki@arizona.edu

Goode, Matt

Saban, Kristen

Wildlife Conservation and Management

School of Natural Resources and Environment

University of Arizona,

Tucson, Arizona USA

Fundamental aspects of a species’ ecology, behavior, physiology, life history, and evolution can be learned from information on diet; however, research on diet is often considered as less important, because it is thought of as too descriptive or lacking in scientific rigor. The fact that diet is an important aspect of a species’ natural history is precisely why we take the time to study it, placing an emphasis on organismal biology with an eye towards the ethological dictum, “know thy animal,” put forth by pioneering behavioral ecologists, such as Konrad Lorenz and Nico Tinbergen. Understanding diet leads to a treasure trove of information about animals, ranging from foraging strategies (e.g., sit-and-wait vs. active foraging), to physiological ecology (e.g., energetics), to fitness consequences related to body condition and reproductive frequency. And from an evolutionary perspective, correlates of diet, such as life history strategies, consequences of body size, and functional morphology (head size and gape limitations) can only be examined if diet is well understood. We present data on diet gleaned from fecal analyses of three syntopic rattlesnakes living in rocky foothills of the Sonoran Desert near Tucson, Arizona. The three species, Tiger Rattlesnake (Crotalus tigris), Black-tailed Rattlesnake (C. molossus) and Western Diamond-backed Rattlesnake (C. atrox) vary in several important ways, including habitat preferences, feeding strategies, venom composition, body size, fecundity, defensive behavior, abundance, and phylogeny. Understanding their diets can shed light on why these differences have evolved and whether competitive interactions among the species may be an organizing force in snake assemblages. We obtained fecal samples from all three species over a 20-year period, allowing for examination of changes in diet related to variation in climatic variables, population of origin, sex, body size, and age-class. We discuss our results in the context of ecological differences among the species, and in response to anthropogenic change due to urbanization. Examining diet of syntopic congeners provides insight into species-specific responses to environmental change that would otherwise be difficult to discern.