Julián A. Velasco

Morphometric analysis of the Rio Apaporis Caiman (Reptilia, Crocodylia, Alligatoridae).

Caiman crocodilus apaporiensis has been considered by several authors as an extreme of morphological variation within the Caiman crocodilus complex. Here, we evaluate its position in the Caiman crocodilus complex morphospace using morphological traits from head shape. We examined the holotype and seventeen paratypes of Caiman crocodilus apaporiensis Medem 1955 deposited at the Field Museum of Natural History. We performed multivariate morphometric analyses: principal component analysis (PCA) and discriminant function analysis (DFA), based on 21 cranial traits of of C. c. apaporiensis, C. yacare and the C. crocodilus complex (C. c. chiapasius, C. c. fuscus andC. c. crocodilus). We find a notable separation of C.c. apaporiensis from C. yacare and C. crocodilus complex in the morphospace. We suggest that geographic isolation might have driven this morphological separation from the C. crocodilus complex, but further analysis are necessary to confirm whether these differences are related with genetic differentiation within the complex. In addition, we suggest that environmental heterogeneity might drive the evolution of independent lineages within the C. crocodilus complex.

Comparative Evolution of an Archetypal Adaptive Radiation: Innovation and Opportunity in Anolis Lizards

Adaptive radiation is a widely recognized pattern of evolution wherein substantial phenotypic change accompanies rapid speciation. Adaptive radiation may be triggered by environmental opportunities resulting from dispersal to new areas or via the evolution of traits, called key innovations, that allow for invasion of new niches. Species sampling is a known source of bias in many comparative analyses, yet classic adaptive radiations have not been studied comparatively with comprehensively sampled phylogenies. In this study, we use unprecedented comprehensive phylogenetic sampling of Anolis lizard species to examine comparative evolution in this well-studied adaptive radiation. We compare adaptive radiation models within Anolis and in the Anolis clade and a potential sister lineage, the Corytophanidae. We find evidence for island (i.e., opportunity) effects and no evidence for trait (i.e., key innovation) effects causing accelerated body size evolution within Anolis. However, island effects are scale dependent: when Anolis and Corytophanidae are analyzed together, no island effect is evident. We find no evidence for an island effect on speciation rate and tenuous evidence for greater speciation rate due to trait effects. These results suggest the need for precision in treatments of classic adaptive radiations such as Anolis and further refinement of the concept of adaptive radiation.

Akaike information criteria and predictive geographical accuracy are not related in ecological niche modeling

Aim Ecological niche modeling (ENM) is an approach used to estimate species‘ presence given its environmental preferences. Model complexity in ENMs has increasingly gained relevance in the last years. In particular, in Maxent algorithm is captured using the Akaike Information Criteria (AIC) based on the number of parameters and likelihoods of continuous raw outputs. However, it is not clear whether best-selected models using AIC are the models with the highest classification rate of correct presences and absences. Here, we test for a link between model complexity and accuracy of geographical predictions of Maxent models. Innovation We created a set of virtual species and generate true geographical predictions for each one. We build a set of Maxent models using presence data from each virtual species with different regularization and features schemes. We compared AICc values for each model with the scores of standard validation metrics (e.g., Kappa, TSS) and with the number of pixels correctly predicted as presences, absences or both. Main Conclusions We found that binary predictions (i.e., presence-absence maps) selected as best models for AIC tend to predict incorrectly sites as presences and absences using independent datasets. We suggest that information criteria as AIC should be avoided when users are interested in binary predictions. Future applications that capture model complexity in ENM applications should be evaluated using standard validation metrics.

Climatic Niche Dynamics and Its Role in the Insular Endemism of Anolis Lizards

Insular systems are usually characterized by have a high species diversity, endemism, and evolutionary uniqueness. Although ecological and evolutionary factors shaping insular diversity and endemism are relatively well established, there is a little understanding about climatic niche dynamics for many insular adaptive radiations. Here, we evaluate the tempo and mode of climatic niche evolution in an iconic insular radiation of lizards. By using an extensive dataset of phylogenetic and coarse-grain climatic niches, we evaluated phylogenetic niche divergence and niche conservatism across temporal and spatial scales in the Caribbean Anolis lizard radiation. We found several instances of niche shifts during the anole radiation across islands. Many of these niche shifts converged to similar climatic regimes between different islands. Furthermore, we find evidence that single-island endemic species are more limited by low suitability of climatic conditions outside its native islands than oceanic barriers due to the high climatic heterogeneity observed at least between Greater Antillean islands. These results suggest that within-lineage climatic niche conservatism has been prevalent in short time scales and likely played a role driving the exceptional insular endemism observed today.

Mapping diversification metrics in macroecological studies: Prospects and challenges

The intersection of macroecology and macroevolution is one of the most active research areas today. Macroecological studies are increasingly using phylogenetic diversification metrics to explore the role of evolutionary processes in shaping present-day patterns of biodiversity. Evolutionary explanations of species richness gradients are key for our understanding of how diversity accumulated in a region. For instance, the present-day diversity in a region can be a result of in situ diversification, extinction, or colonization from other regions, or a combination of all of these processes. However, it is unknown whether these metrics capture well these diversification and dispersal processes across geography. Some metrics (e.g., mean root distance -MRD-; lineage diversification-rate -DR-; evolutionary distinctiveness -ED-) seem to provide very similar geographical patterns regardless of how they were calculated (e.g., using branch lengths or not). The lack of appropriate estimates of extinction and dispersal rates in phylogenetic trees can limit our conclusions about how species richness gradients emerged. With a review of the literature and complemented by an empirical comparison, we show that phylogenetic metrics by itself are not capturing well the speciation, extinction and dispersal processes across the geographical gradients. Furthermore, we show how new biogeographic methods can improve our inference of past events and therefore our conclusions about the evolutionary mechanisms driving regional species richness. Finally, we recommend that future studies include several approaches (e.g., spatial diversification modelling, parametric biogeographic methods) to disentangle the relative the role of speciation, extinction and dispersal in the generation and maintenance of species richness gradients.