Climatic niche breadth, range size, and habitat specialization in otters
Identifying species responses to environmental changes is necessary to preserve biodiversity in a changing world. Key to this process is understanding the variables that affect species distributions, such as climate and evolutionary history. Here we determine how climatic niches differ between ecologically similar species, and whether differences are informed by evolutionary relationships. To address these questions we use members of the subfamily Lutrinae (otters), species which are important to conservation but are often understudied. The diversity in occupied environments and range size between species makes them an interesting taxon to examine the relationship between environment, range size, and niche breadth, variables which may affect species persistence in the face of environmental change. In this study, we examine otter species distributions to determine which variables most strongly predict otter presence. To characterize their climatic niche we built species distribution models (SDMs) for five species of otters. We paired species occurrence data from GBIF with present-day climate data from WorldClim, and ran Generalized Linear Models and Random Forest using the R package “BIOMOD2”. After determining the best variables and models for each species, we determined climatic niche breadth, and whether explanatory variables were similar for closely related species.
Preliminary results indicate there is a strong relationship between climatic niche size, range size, and habitat specialization in otters. Lontra canadensis and Lutra lutra have broad ranges, are abundant, and have the broadest niches (e.g., their climatic niche is described by 15 explanatory variables each and they occupied a wide range of values for most variables). Lontra longicaudis also has a broad range but is more patchily distributed, and requires fewer (11) explanatory variables. Lontra provocax has a small range, but occupies various habitats, reflected by a niche explained by 10 variables. Pteronura brasiliensis has a moderately large but fairly homogenous range explained by 4 variables. Evolutionary relationships may affect the climatic niche: the most evolutionarily distinct species (Pteronura brasiliensis) has a significantly different climatic niche, and members of the genus Lontra are more similar to each other than to other species. Temperature and precipitation contribute relatively equally to niche breadth in all but Lutra lutra, for which temperature is a greater predictor. Our next steps are to further refine the models and add other explanatory variables. Overall, this study provides a better understanding of the relationships of otters to climate and how evolutionary relatedness may affect these relationships.