The research team, drawing on field records collected between 1980 and 2021, analyzed stomach contents and direct predation observations from 127 individual snakes. The sample included 13 spotted dwarf boas (Tropidophis pardalis), 28 banded dwarf boas (T. semicinctus), and 86 black-tailed dwarf boas (T. melanurus), the latter split into 80 large individuals and just 6 small ones. Every snake in the dataset had consumed a single prey item, which made the comparisons unusually clean. The study area covered roughly 258 square kilometers of dry, rocky lowland shrubland known locally as cuabal, along with pastures, eucalyptus plantations, and suburban edges, all sampled mostly during the rainy season when vertebrate prey is most active.

The headline finding is stark. Tropidophis pardalis, T. semicinctus, and small T. melanurus showed complete overlap in diet composition, and all three specialized almost entirely on lizards of the genus Anolis, the ubiquitous anoles of the Caribbean. Statistical tests comparing the frequency of amphibian versus lizard prey among these three categories returned a P-value of exactly 1, meaning there was no detectable difference whatsoever. In practical terms, a small black-tailed dwarf boa, a spotted dwarf boa, and a banded dwarf boa sitting on the same hillside are all hunting the same two anole species, Anolis sagrei and Anolis ophiolepis, with essentially no dietary distinction between them.

Large Tropidophis melanurus tell a very different story. Adults of this species, the largest in the genus at more than a meter in snout-vent length, consumed amphibians for 95 percent of their diet. The Cuban treefrog (Osteopilus septentrionalis) alone made up roughly 70 percent of their prey records, with two species of endemic toads of the genus Peltophryne accounting for another 26 percent. Mammals such as house mice and black rats, and a single bird, appeared only occasionally. When the researchers compared small and large T. melanurus statistically, the difference was overwhelming, with P-values on the order of 10 to the minus 9. The result is a textbook ontogenetic dietary shift: juveniles start life as anole specialists and pivot to frogs and toads as their bodies and gapes grow.

That shift matters because of the sheer scale of size difference within T. melanurus. Newborns measure around 230 millimeters in snout-vent length and weigh about 4 grams, while large adults exceed a meter and 800 grams. Gape limitation, the physical constraint of mouth size on what a snake can swallow, is a well-documented driver of dietary change in snakes, and this species pushes that principle to an extreme. The authors note that individuals around 350 millimeters in total length, less than a year old, already belong to the small class, and that ex situ observations show specimens of modest size accepting mice and even a House Sparrow, hinting that the switch to vertebrate prey beyond anoles begins earlier than stomach records alone suggest.

To quantify specialization, the team applied Levins’ standardized niche breadth index, a measure ranging from 0, when every individual uses a single resource, to 1, when all resources are used equally. Three categories scored the lowest possible value of B-prime equals 0: T. pardalis, T. semicinctus, and small T. melanurus, each eating nothing but anoles. Even large T. melanurus, the broadest feeder in the assemblage, scored only 0.280 when frogs, toads, birds, and mammals were treated as separate resource states. Every category in the study fell below 0.3, indicating that these snakes are all trophic specialists, not generalists, despite the reputation of T. melanurus as the flexible feeder of the genus.

The complete dietary overlap among three coexisting species raises an obvious question: why doesn’t competition eliminate one of them? The competitive exclusion principle, formalized by Gause in 1934, holds that two species using the same limiting resource in the same way cannot stably coexist. The authors argue that the answer likely lies along a different niche axis altogether: space. Body shape in snakes is a reliable predictor of habitat use. Stocky snakes with circular cross-sections tend to be terrestrial, while slender, laterally compressed ones tend to climb. Tropidophis pardalis fits the terrestrial template, T. semicinctus fits the semi-arboreal one, and T. melanurus sits morphologically in between.

Field observations support this spatial interpretation. The researchers report having watched T. semicinctus actively foraging in vegetation more than two meters above the ground on well over a hundred occasions, apparently hunting sleeping anoles at night, while T. pardalis hunts at ground level. Crucially, the anoles themselves are habitat generalists: Anolis sagrei occupies everything from under rocks and low grass to heights above two meters, which gives each snake species access to the same prey in its own preferred stratum. The authors also point out that both anole prey species can be locally very abundant, so the shared resource may simply be plentiful enough to support all three predators. Notably, these dwarf boas even share resting sites, underscoring how little their daily lives diverge.

The feeding behavior records add texture to the picture. Most snakes in the dataset were inactive individuals with stomach contents, but nine were caught in the act. A juvenile T. semicinctus was found swallowing a Cuban Brown Anole under a lifted rock at 9:42 in the morning. A very large T. melanurus, roughly a meter long, was seen constricting an Eastern Giant Toad around 7 a.m. and only finished swallowing it around 1 p.m., suggesting the capture happened before dawn. Six other large T. melanurus were observed subduing Cuban treefrogs. Nearly all predation events occurred at night, consistent with the genus’s mainly nocturnal habits.

The study is the first detailed test of dietary segregation in a Cuban Tropidophis assemblage, a genus of 33 species with 17 endemic to Cuba, the only place where several species co-occur. The authors caution that the sample of small T. melanurus is limited to six individuals, and that habitat use and activity time remain formally untested, so the spatial segregation hypothesis still needs direct confirmation. They also note that rarer prey types, including Eleutherodactylus frogs and introduced geckos, may be consumed at low frequencies that the sampling did not capture. Still, the core message stands: in this corner of Cuba, niche partitioning among dwarf boas appears to be carved more into where they hunt than into what they eat, and the sharpest dietary boundary in the community runs not between species but between childhood and adulthood in a single, size-shifting snake.

Subject of Research: Dietary niche overlap and ontogenetic diet shift in sympatric Cuban dwarf boas (Tropidophis)

Article Title: Co-occurring Cuban dwarf boas ( Tropidophis ) show limited dietary differentiation

Article References: Rodríguez-Cabrera, T. M., Torres, J., & Morell Savall, E. (2025). Co-occurring Cuban dwarf boas (Tropidophis) show limited dietary differentiation. Herpetozoa, 38, 215-223. https://doi.org/10.3897/herpetozoa.38.e144100

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.38.e144100

Keywords: Tropidophis, dwarf boas, Cuba, niche partitioning, ontogenetic diet shift, Anolis, herpetology, trophic niche breadth, snakes, Cuban treefrog, ecology, Villa Clara