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

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.

Evolutionary history of the flora of Mexico: Dry forests cradles and museums of endemism

“…Patterns of WE and WPE were similar, and particularly for endemism are consistent with earlier research on a number of taxonomic groups: (i) ferns, in which species richness was identified in the SE and in Chiapas, and weighted endemism in several areas in the Sierra Madre Oriental, in the Trans‐Mexican Volcanic Belt and Sierra Madre del Sur (Sanginés‐Franco et al, ); (ii) gymnosperms, for which areas of endemism coincided in the Sierra Madre Oriental and a small area in Oaxaca (Contreras‐Medina & Luna‐Vega, ); (iii) the monocot tribe Tigridieae (Iridaceae), for which endemism coincided in the eastern part of the Trans‐Mexican Volcanic Belt and the Sierra Madre Oriental, as well as in the Tehuacán Valley and in the Sierra Madre del Sur (Munguía‐Lino et al, ); (iv) oaks, Quercus spp., for which areas of endemism were identified in the Sierra Madre Occidental and in the Trans‐Mexican Volcanic Belt (Rodríguez‐Correa et al ); (v) the genus Bursera in which three areas of endemism were identified on the Central Mexican Pacific Coast, in the western Balsas River Basin and in the Tehuacán Valley (De‐Nova et al, ; Gámez et al, ); and (vi) cacti from the Chihuahuan Desert where high degrees of endemism were identified on the Mexican Plateau, as well as in the southern area of the Sierra Madre Oriental (Hernández & Gómez‐Hinostrosa, ). In addition, for one functional group, the monocot geophytes, significant areas of endemism were identified in the Trans‐Mexican Volcanic Belt, the Sierra Madre Oriental, and in the Tehuacán Valley, which also agrees with our results (Sosa & Loera, ). Moreover, the southernmost mountainous area in the Baja California peninsula was identified as having high degree of endemism (Riemann & Ezcurra, ).…”

“…Georeferences were obtained following two approaches. For the vascular non‐endemic species we consulted the Global Biodiversity Information Facility (GBIF) (http://www.gbif.org), and for endemic species, records were supplemented with: (i) our previous research (Sosa & De‐Nova, ; Gándara & Sosa, ; Sosa & Loera, ); (ii) consulting specimens from Mexican herbaria (ANSM, ENCB, IBUG, IEB, MEXU, and XAL; acronyms based on Thiers, , http://sweetgum.nybg.org/science/ih/); and (iii) consulting additional biodiversity databases such as SEINet (http://swbiodiversity.org/seinet), and Tropicos (http://www.tropicos.org). The identity of records was verified prior to their inclusion in the database.…”

“…Here many endemic taxa coincided, some found in seasonally tropical dry forests and pine-oak forests, with many ferns in the Dryopteridaceae (Thelipteris, Phanerophlebia), and dominated by endemic Asteraceae (Digitacalia, Henricksonia, Iostephane, Loxothysanus, Villasenoria), Burseraceae, Fabaceae (Cannavalia, Coursetia, Dalea, Mimosa, Phaseolus, Piptadenia), coinciding with monocots like Nothoscordum Zepyrhanthes, Milla, Agave, Calochortus, and some orchids (Govenia, Bletia). (Sosa & Loera, 2017). Moreover, the southernmost mountainous area in the Baja California peninsula was identified as having high degree of endemism (Riemann & Ezcurra, 2007).…”

“…2). Earlier research has focused solely on endemism for certain plant groups such as the Tigridieae (Iridaceae), Bursera, oaks, cacti, monocot geophytes and ferns, and a number of studies have focused on patterns of species richness and endemic taxa in certain regions of Mexico (D avila-Aranda et al, 2004;Contreras-Medina & Luna-Vega, 2007;Riemann & Ezcurra, 2007;Hern andez & G omez-Hinostrosa, 2011;De-Nova et al, 2012;G amez et al, 2014;Rodr ıguez-Correa et al, 2015;Sangin es-Franco et al, 2015;Mungu ıa-Lino et al, 2016;Sosa & Loera, 2017;De-Nova et al, 2018). The majority of these studies identified the southern regions of the Sierra Madre Oriental and Sierra Madre Occidental mountain ranges, the Trans-Mexican Volcanic Belt and the Tehuac an Valley as having high degrees of endemism.…”

Richness, geographic distribution patterns, and areas of endemism of selected angiosperm groups in Mexico

“…This pattern is similar to the results obtained by others (Cruz-C ardenas et al, 2013;Vargas-Amado et al, 2013;Mungu ıa-Lino et al, 2015;Villaseñor, 2016). The richness analyzes on the Mexican (Cu ellar-Mart ınez & Sosa, 2016) and Mesoamerican monocotyledonous geophytes (Sosa & Lorea, 2017) uncovered the same pattern.…”