Population dynamics of Equus conversidens (Perissodactyla, Equidae) from the late Pleistocene of Hidalgo (central Mexico): Comparison with extant and fossil equid populations

Abstract

The Mexican horse Equus conversidens is a representative member of the Quaternary North American megafauna. Systematics, phylogeny, and stable isotope ecology of this species are known in some detail, although information regarding population ecology is unexplored. Numerous fossil remains (isolated teeth, mandibles, skulls, and postcranial elements) of this horse have been collected from Pleistocene deposits that outcrop at southeastern Hidalgo, central Mexico. The available dental sample is suitable for recovering some aspects of its population dynamics. Our study compares life history traits of cohorts of E. conversidens from the state of Hidalgo to extant and Pleistocene species of equids from North America (United States and Canada), Europe (France), and Africa (Rwanda, Namibia). Life tables and age-structured models allow us to describe demographic parameters and mortality patterns. We highlight that E. conversidens was a typical K-strategist with high probability of surviving to adulthood with asymptotic growth rate (λ = 1.05) indicating a population close to balance. Considering the mammalian associations from different habitats in southeastern Hidalgo and the flexible diet of E. conversidens, we suggest that ambush (Panthera atrox) and cursorial predators (Canis dirus) played a major role in the prime-dominated mortality pattern of this species. The presence of a woodland-grassland ecosystem that sustained a high diversity of herbivores and the occurrence of large-sized predators suggest that the population dynamics were regulated by resource availability and selective predation, as it occurs in populations of the extant plains zebra, E. quagga.