Abstract

The Chihuahuan Desert Biome (CDB), the largest semi-arid region in North America, has undergone repeated climatic fluctuations during the Interglacial–Glacial Oscillation (IGO) of the last eight million years. We investigated biogeographic and evolutionary patterns of endemic cacti within the present-day Interglacial and the Last Glacial by examining 119 strict endemics, including 75 suitable for Species Distribution Modeling (SDM) and 44 microareal strict endemics, together representing 36.17% of the 329 species in the biome. Cacti probably originated in South America after substantial separation from Africa, with pollen fossils documenting their presence in Mexico by 51.6 Ma. Climatic reconstructions for each phase were developed using regional numerical and co-kriging methods following Sánchez-Santillán and García, complemented by paleoclimatic evidence from Scotese, Roy-Priyadarsi, Van Devender, and Betancourt. MAXENT SDMs and PANBIOTRACKS’ track-node analyses were applied to 3719 specimens representing 2015 localities to explore the colonization patterns and broad evolutionary trends. Combined suitability layers and panbiogeographic analyses revealed a predominant southeastern-to-northwestern colonization pattern, largely following the western flank of the Sierra Madre Oriental and intermontane valleys. The northern sectors were less diverse, more arid, and apparently colonized more recently, whereas the southern sectors concentrated much of the endemic richness and connectivity. The concordance among climatic suitability patterns, tracks, nodes, and the available phylogenetic evidence supports a major role of climatic oscillations in shaping the spatial and evolutionary history of endemic cacti throughout the CDB.

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