Influence of current climate, historical climate stability and topography on species richness and endemism in Mesoamerican geophyte plants.

Victoria Sosa,Israel Loera

doi:10.7717/peerj.3932

Abstract

BackgroundA number of biotic and abiotic factors have been proposed as drivers of geographic variation in species richness. As biotic elements, inter-specific interactions are the most widely recognized. Among abiotic factors, in particular for plants, climate and topographic variables as well as their historical variation have been correlated with species richness and endemism. In this study, we determine the extent to which the species richness and endemism of monocot geophyte species in Mesoamerica is predicted by current climate, historical climate stability and topography.MethodsUsing approximately 2,650 occurrence points representing 507 geophyte taxa, species richness (SR) and weighted endemism (WE) were estimated at a geographic scale using grids of 0.5 × 0.5 decimal degrees resolution using Mexico as the geographic extent. SR and WE were also estimated using species distributions inferred from ecological niche modeling for species with at least five spatially unique occurrence points. Current climate, current to Last Glacial Maximum temperature, precipitation stability and topographic features were used as predictor variables on multiple spatial regression analyses (i.e., spatial autoregressive models, SAR) using the estimates of SR and WE as response variables. The standardized coefficients of the predictor variables that were significant in the regression models were utilized to understand the observed patterns of species richness and endemism.ResultsOur estimates of SR and WE based on direct occurrence data and distribution modeling generally yielded similar results, though estimates based on ecological niche modeling indicated broader distribution areas for SR and WE than when species richness was directly estimated using georeferenced coordinates. The SR and WE of monocot geophytes were highest along the Trans-Mexican Volcanic Belt, in both cases with higher levels in the central area of this mountain chain. Richness and endemism were also elevated in the southern regions of the Sierra Madre Oriental and Occidental mountain ranges, and in the Tehuacán Valley. Some areas of the Sierra Madre del Sur and Sierra Madre Oriental had high levels of WE, though they are not the areas with the highest SR. The spatial regressions suggest that SR is mostly influenced by current climate, whereas endemism is mainly affected by topography and precipitation stability.ConclusionsBoth methods (direct occurrence data and ecological niche modeling) used to estimate SR and WE in this study yielded similar results and detected a key area that should be considered in plant conservation strategies: the central region of the Trans-Mexican Volcanic Belt. Our results also corroborated that species richness is more closely correlated with current climate factors while endemism is related to differences in topography and to changes in precipitation levels compared to the LGM climatic conditions.

Highlights

There is renewed interest in identifying centers of species richness and endemism because understanding the genesis of diversification makes it possible to identify the processes that maintain biodiversity and with this knowledge, strategies for long term conservation can be formulated (Brooks et al, 2006; Murray-Smith et al, 2009)
SR and weighted endemism (WE) had similar geographic patterns, some important differences were observed in different mountainous regions of Mexico such as the Sierra Madre del Sur, Chiapas and Sierra Madre Oriental that had some of the highest levels of endemism but did not coincide with the highest species richness for the direct estimates based on occurrence data
For plants, inventory is incomplete for many groups and many regions or species have very restricted distributions with a few records and this might affect the reliability of environment-spatial prediction of species richness (e.g., Yan, Yang & Tang, 2013; Meyer, Weigelt & Kreft, 2016)

Summary

Introduction

There is renewed interest in identifying centers of species richness and endemism because understanding the genesis of diversification makes it possible to identify the processes that maintain biodiversity and with this knowledge, strategies for long term conservation can be formulated (Brooks et al, 2006; Murray-Smith et al, 2009). In particular for plants, climate and topographic variables as well as their historical variation have been correlated with species richness and endemism. We determine the extent to which the species richness and endemism of monocot geophyte species in Mesoamerica is predicted by current climate, historical climate stability and topography. Our estimates of SR and WE based on direct occurrence data and distribution modeling generally yielded similar results, though estimates based on ecological niche modeling indicated broader distribution areas for SR and WE than when species richness was directly estimated using georeferenced coordinates. Both methods (direct occurrence data and ecological niche modeling) used to estimate SR and WE in this study yielded similar results and detected a key area that should be considered in plant conservation strategies: the central region of the Trans-Mexican Volcanic Belt.

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Conclusion