Ever since the seminal papers by Williams and Rand, the Anolis radiation across the West Indies has increasingly established itself as an alluring example of ecomorphological convergence. Considering an Anolis community on one island, co-occurring species have undergone niche partitioning, whereby each species has evlved particular behavioral, morphological, and ecological traits well-adapted for the microhabitat it occupes. Pop over to another island, and voilà, similar sets of ecomorphs can be found— their resemblance so striking and uncanny.
But the Anolis story isn’t clean cut. Studies of mainland anoles have yielded equivocal findings for whether they also conform to the beautiful patterns observed in the Caribbean. Much baseline data on mainland Anolis communities are needed to determine the extent to which convergence occurs and what factors drive differences in community structure. To partly address this gap, Jonathan Losos, Anthony Herrel, Ambika Kamath, and I recently published a paper describing the ecological morphology of anoles in a tropical lowland rainforest in Costa Rica, at La Selva Biological Station (download).
Accumulating field observations from four field seasons ranging from 2005 to 2017, we draw from over 1000 observations to characterize the habitat use of eight Anolis species that occur at La Selva. These species include Anolis humilis, Anolis limifrons, Anolis lemurinus, Anolis oxylophus, Anolis capito, Anolis carpenteri, Anolis biporcatus, and Anolis pentaprion, and we opted to devote a brief section to Polychrus gutturosus. Our results revealed overlapping niches and substantial variability in habitat use across many species. Furthermore, the morphologies of A. humilis and A. limifrons were at odds with microhabitat use following the predictions of Caribbean anole ecomorphology. Among the two most abundant species, relative hindlimb length was greater for the more arboreal A. limifrons, whereas it was shorter for the more terrestrial A. humilis.
If mainland and island anoles exhibit divergent ecomorphological patterns, this begs the question of how selective pressures differ between mainland and island habitats to drive these differences. Andrews proposed that predation may more strongly influence Anolis diversification on the mainland, because in comparison to islands, predators are far more abundant, anole population densities are lower, and arthropod prey is plentiful. In contrast, Caribbean anoles are thought to be food limited, and there may be stronger selection for niche partitioning. Through examining variation in species’ habitat use relative to the abundance of other co-occurring species at La Selva, our data suggests a low level of interspecific competition for this mainland community, corroborating the hypotheses Andrews set forth.
In recent years, the study of mainland anoles has received more attention. We are in great need of ecological, morphological, and life history trait data for Anolis communities throughout Central and South America to further our understanding of the evolutionary trajectories of mainland and island anoles. So, anole biologists, you can throw out your boats and steer clear of the oceanic divide!
More recently, I had the opportunity to revisit La Selva, and of course, I had a wonderful time reacquainting myself with the anoles 🙂 Photographs from 2021 are interspersed in this post and continue below.