Why most Caribbean Anolis species are endemic to a single island?

One of the most interesting patterns in the insular anole radiation is the observation that the majority of species are single-island endemics (150 of out 166 species). This observation in the Caribbean anole lizards has been known from a while and several studies have attempted to establish the underlying causes of this striking pattern (e.g., 1, 2, 3).

In a recent study, as part of my PhD dissertation, I used a different approach to try to understand why most of these species are unable to colonize other islands. I used a recently developed conceptualization to link abundances and ecological niche requirements at coarse-grain scales, this approach has been developed in the lab of my advisor (see 4, 5, 6; but see 7, 8, 9 for discussions and counter-examples; this approach has been strongly debated in the literature in the last years).

We used ecological niche modeling -ENM- to predict species’ distributions across all Caribbean islands for each species with at least 10 occurrence records. We estimated the position of each pixel predicted as presence in the ecological space using Euclidean distances. In short, we characterize all pixels for a single species and calculated which of these were close to the niche centroid (which we assume as the best conditions for species presence) and which were close to the niche periphery (see Figure 1). We predicted that pixels predicted by ENM as presences within each native island will be more close to the niche centroid and those predicted as presences in other islands will be in the periphery of the niche.

 

NicheSpace.png

Figure 1. Available climatic space showing the position of each pixel predicted from ecological niche modeling across islands.

We found that many species follow the predicted pattern; in other words, we found that the “best” niche conditions are in the native islands regardless of climatic heterogeneity observed in each island and the “worst” niche conditions are outside native islands. We also used other metrics to corroborate our results. We interpreted these results as  instances of recent climatic niche conservatism (within lineages) and therefore this operates as a constraint in the ability of each species to colonize other islands (i.e. due to the low suitable climatic conditions for successful population establishment). We only gathered data for 70 species and therefore it will be necessary more data and more studies (including physiological experiments) to corroborate our assertions.

Also, we examined the pattern of realised climatic niche shifts across the anole radiation and we found evidence of several instances of climatic niche convergence. We concluded that anoles evolved to occupy different portions of the climate space and in several cases evolved quickly to occupy some portions of this space (e.g., cold climatic conditions) and recently most of these species likely adapted very well to climatic conditions in its native islands.

The paper was published here:

https://link.springer.com/article/10.1007%2Fs11692-018-9455-x

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