Abstract
Megafaunas worldwide have been decimated during the late Quaternary. Many extirpated species were keystone species, and their loss likely has had large effects on ecosystems. Therefore, it is increasingly considered how megafaunas can be restored. The horse (Equus ferus) is highly relevant in this context as it was once extremely widespread and, despite severe range contraction, survives in the form of domestic, feral, and originally wild horses. Further, it is a functionally important species, notably due to its ability to graze coarse, abrasive grasses. Here, we used species distribution modelling to link locations of wild-living E. ferus populations to climate to estimate climatically suitable areas for wild-living E. ferus. These models were combined with habitat information and past and present distributions of equid species to identify areas suitable for rewilding with E. ferus. Mean temperature in the coldest quarter, precipitation in the coldest quarter, and precipitation in the driest quarter emerged as the best climatic predictors. The distribution models estimated the climate to be suitable in large parts of the Americas, Eurasia, Africa, and Australia and, combined with habitat mapping, revealed large areas to be suitable for rewilding with horses within its former range, including up to 1.5 million ha within five major rewilding areas in Europe. The widespread occurrence of suitable climates and habitats within E. ferus’ former range together with its important functions cause it to be a key candidate for rewilding in large parts of the world. Successful re-establishment of wild-living horse populations will require handling the complexity of human–horse relations, for example, potential conflicts with ranchers and other agriculturalists or with other conservation aims, perception as a non-native invasive species in some regions, and coverage by legislation for domestic animals.
Highlights
During the late Quaternary, megafaunas worldwide have been decimated [1]
The Maximum Entropy (MAXENT) species distribution modelling indicated that the occurrence of wild-living E. ferus is related to mean temperature in the coldest quarter (MTCQ), precipitation in the driest quarter (PDQ) and precipitation in the coldest quarter (PCQ), with MTCQ as the strongest predictor, followed by PDQ (Fig 3C)
The model validation showed the two models to have True Skill Statistic (TSS) 0.410: A model comprised of all three predictor variables and a model including MTCQ and PDQ (Table 2)
Summary
During the late Quaternary, megafaunas worldwide have been decimated [1]. It is increasingly clear that humans have played a key role in these losses [2,3,4], and human-driven megafaunaPLOS ONE | DOI:10.1371/journal.pone.0132359 July 15, 2015A Geographic Assessment of the Global Scope for Rewilding with Horses losses are still ongoing, e.g., with a great proportion of extant perissodactyl species extinct in a large part of their historical range and/or declining and severely threatened (14 out 16 species) [5]. Large herbivores and carnivores can have large impacts on ecosystems, often serving as keystone species and ecosystem engineers [6, 7], and the megafauna losses have had profound effects on ecosystems [8,9,10]. Reintroduction of extirpated species or functional types of high ecological importance to restore self-managing functional, biodiverse ecosystems (rewilding) is increasingly being discussed and implemented [11]. Rewilding is being implemented in various ways, notably at varying spatial scales and with varying degrees of ongoing human interventions [11]. Scale and potential human-wildlife conflicts are some of the factors that require consideration, as do ecological effects when reintroducing species that have been absent for thousands of years [12,13,14,15,16]
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