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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.

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In this study we selected the New World species of Ephedra to understand the ecological consequences of different dispersal syndromes. The twenty‐three species of Ephedra in the New World have a disjunct distribution in North and South American arid and semi‐arid habitats, exhibiting three dispersal syndromes related to dispersal by birds, wind and rodents. Using DNA sequence data we inferred phylogenetic relationships and lineage divergence times, and used these estimates to test different ecological assumptions. Using comparative methods we tested for correlations between dispersal syndromes and a set of ecological variables (niche breadth, niche evolution, distributional ranges and niche position). We found that speciation events in the New World coincided with the expansion of arid habitats in this region. We suggest that the bird dispersal syndrome is related with higher rates of climatic niche evolution for all variables used, including aridity index, mean annual temperature and mean annual precipitation. Distribution ranges were correlated with niche breadth, they were however not significantly different between dispersal syndromes. Species inhabiting the extremely arid regions on niche axes had narrower niche breadths. We conclude that species whose seeds are dispersed by birds have colonized a broader set of habitats and that those with wind and rodent dispersal syndromes might have promoted the colonization of more arid environments.

Aim We investigate the influence of late Neogene orogenic activity and Pleistocene glacial‐interglacial cycles on intraspecific divergence and demographic history in the gymnosperm shrub Ephedra compacta. We test refugia hypotheses to explain geographical patterns of genetic diversity and phylogeographic structure in a warm North American desert that reaches inter‐tropical latitudes. Location Chihuahuan Desert, Mexican Plateau, Sierra Madre Oriental, Tehuacán Valley. Methods Geographical patterns of genetic diversity were estimated using chloroplast DNA sequences of 191 individuals from 24 populations. AMOVA and SAMOVA analyses were used to assess population and phylogeographic structure, respectively. Approximate Bayesian computation (ABC) was implemented to test phylogeograhic scenarios of population divergence and demographic expansion. Ecological niche modelling (ENM) was performed to predict the potential distribution of E. compacta during the late Pleistocene and to estimate historical habitat stability. Refugia hypotheses were tested by estimating the linear associations between habitat stability, latitude and parameters of genetic diversity. Results High levels of population and phylogeographic structure were observed with six geographical groups explaining most of the variation. The best‐supported phylogeographic scenario assumed population divergence and demographic expansion during the Pleistocene. ENM predictions showed historical changes in the potential distribution of E. compacta, with a broader geographical extent in the present. Habitat stability was positively associated with population genetic diversity. Main conclusions The intraspecific population divergence and demographic expansion in E. compacta is probably associated with the glacial‐interglacial cycles of the Pleistocene. Our ENM predictions also support a scenario of habitat contraction and expansion during this time period. The phylogeographic history of E. compacta is predicted by climate refugia dynamics in which specific areas, primarily in the Mexican Plateau harbour the highest levels of habitat stability and genetic diversity.