Effects of body size, diet, and transience on the demography of the arboreal boid snake Corallus grenadensis on Carriacou (Grenada Grenadines, West Indies)

• Published in: Population ecology 2021-04, Vol.63 (2), p.177-188
• Main Authors: Henderson, Robert W., Hileman, Eric T., Sajdak, Richard A., Harrison, Billie C., Powell, Robert, Bradke, Danielle R.
• Format: Article
• Language: English
• Subjects: Abundance; Body size; Capture-recapture studies; capture‐recapture; Confidence intervals; Corallus grenadensis; Demography; Diet; Food sources; growth; Lizards; Neotropics; Ontogeny; Population density; Prey; Snakes; Species; Survival
• ISSN: 1438-3896; 1438-390X
• DOI: 10.1002/1438-390X.12079

Remarkably little is known about the demography of snakes in the family Boidae. This lack of information may be attributed, in part, to low population densities on the Neotropical mainland, rendering capture‐recapture methods impractical for many species. Conversely, islands support fewer species but snake densities can be much higher. Corallus grenadensis is an arboreal boid endemic to the Grenada Bank and, relative to mainland boids, can be amazingly abundant. As young, its diet is comprised largely of native Anolis lizards, a ubiquitous and abundant food source; it then undergoes an ontogenetic shift in diet to a less abundant resource, rodents. From 2015 to 2019, we marked 254 C. grenadensis and used capture–recapture models to estimate abundance, capture probabilities, survival, and the proportion of transients. We hypothesized that the transient effect would increase with body size (snout–vent length [SVL]), prompted by their ontogenetic shift in diet. Capture probabilities increased with sampling effort and decreased with increasing SVL. Abundance ranged from 96 to 141 individuals and annual resident survival was 0.71, 95% confidence interval (CI) = 0.54–0.83. The proportion of transients increased with increasing SVL, with the estimate being distinguishable from zero starting at ~810 mm SVL, coinciding with the size at which their dietary shift from ectothermic to endothermic prey begins. Ontogenetic dietary shifts are widespread in snakes and occur in at least 11 of 17 species of West Indian boids. Thus, the prominence of transients in our study may be indicative of its demographic and ecological importance among other snake species. Ontogenetic dietary shifts are widespread in snakes and occur in at least 11 of 17 species of West Indian boids, including Corallus grenadensis, an arboreal boid endemic to the Grenada Bank. Using capture–recapture methods, we estimated C. grenadensis abundance, survival, and proportion of transients, and provided supporting evidence to link the proportion of transients to an ontogenetic shift from ectothermic to endothermic prey. Our study fills knowledge gaps in boid demography and provides insights into the potential importance of dietary ontogeny in regulating foraging and movement patterns in snake populations.