Sympatric Masticophis flagellum and Coluber constrictor Select Vertebrate Prey at Different Levels of Taxonomy
Masticophis flagellum (Coachwhip) and Coluber constrictor (Eastern Racer) are widespread North American snakes with similar foraging modes and habits. Little is known about the selection of prey by either species, and despite their apparently similar foraging habits, comparative studies of the foraging ecology of sympatric M. flagellum and C. constrictor are lacking. We examined the foraging ecology and prey selection of these actively foraging snakes in xeric, open-canopied Florida scrub habitat by defining prey availability separately for each snake to elucidate mechanisms underlying geographic, temporal, and interspecific variation in predator diets. Nineteen percent of M. flagellum and 28% of C. constrictor contained stomach contents, and most snakes contained only one prey item. Mean relative prey mass for both species was less than 10%. Larger C. constrictor consumed larger prey than small individuals, but this relationship disappeared when prey size was scaled to snake size. Masticophis flagellum was selective at the prey category level, and positively selected lizards and mammals; however, within these categories it consumed prey species in proportion to their availability. In contrast, C. constrictor preyed upon prey categories opportunistically, but was selective with regard to species. Specifically, C. constrictor positively selected Hyla femoralis (Pine Woods Treefrog) and negatively selected Bufo quercicus (Oak Toad), B. terrestris (Southern Toad), and Gastrophryne carolinensis (Eastern Narrowmouth Toad). Thus, despite their similar foraging habits, M. flagellum and C. constrictor select different prey and are selective of prey at different levels of taxonomy.Abstract
Occurrence of prey categories consumed by Masticophis flagellum (n = 20) and Coluber constrictor (n = 56) expressed as a proportion of snakes of each species that consumed each prey category. Numbers above bars indicate the number of individuals of each prey category that were consumed. Proportions for C. constrictor do not sum to one because four individuals contained both amphibians and lizards in their stomachs.
Occurrence of prey species consumed by Masticophis flagellum (n = 20) and Coluber constrictor (n = 55) expressed as a proportion of snakes of each species that consumed each prey species. Numbers above bars indicate the number of individuals of each prey species that were consumed. Abbreviations used are: Agry = Acris gryllus, Hfem = Hyla femoralis, Rcap = Rana capito, Rspp = Rana catesbeiana + R. grylio, Rutr = Rana utricularia, Acar = Anolis carolinensis, Asex = Aspidoscelis sexlineata, Pine = Plestiodon inexpectatus, Swoo = Sceloporus woodi, Pflo = Podomys floridanus, and Ppol = Peromyscus polionotus. Proportions do not sum to one because some individual snakes contained more than one prey species.
Relationship between prey category and predator size (snout–vent length) for Masticophis flagellum and Coluber constrictor. Each point represents a single snake. Four individual C. constrictor that contained both amphibians and lizards appear in both categories.
Ln-transformed prey mass as a function of ln-transformed snake mass for Masticophis flagellum (dashed line; adjusted R2 = −0.067, F1,6 = 0.56, P = 0.48) and Coluber constrictor (solid line; adjusted R2 = 0.36, F1,34 = 20.44, P < 0.0001). Only individual snakes that contained relatively intact prey were included in this analysis (M. flagellum: n = 8, C. constrictor: n = 36).
Contributor Notes
Associate Editor: J. D. Litzgus.