Low conservatism of the climatic niche of sea turtles and implications for predicting future distributions

Abstract

Understanding how the ecological niches of species are formulated across space is critical for modeling the current and predicting future distributions under climate change. Here, we examine how stable are the realized niches of distinct populations of the endangered green sea turtle (Chelonia mydas) which are defined on the basis of genetic and demographic data and are distributed around the globe. We used 906 georeferenced records of green turtle nesting sites that are embedded within eight Regional Management Units to compare climatic niche for each one of the distinct units. We used an asymmetric overall index and a decision‐tree model to assess niche conservatism through a comparison of temperature‐ and precipitation‐based bioclimatic variables that characterize the climatic niche breadth of the spatially distinct population segments. We found a high degree of variance in climatic space, which also lacks any latitudinal pattern. Environmental determinants vary significantly across the studied population units: variables that have been long‐recognized as critical for nesting (e.g., maximum temperature of the warmest month) showed only low overlap between some of different regional entities. Our results contribute substantially to the current debate on the predictive power of species distribution models that use only climate variables as predictors when aggregating data from various populations. We argue that studies on climatic‐niche evolution and divergent ecological selection mechanisms are required before attempting to identify suitable habitats for a species, describe climatic widths and search for plausible expansions of geographical shifts attributed to climate change.