The five MAXENT models for wild-living <i>E</i>. <i>ferus</i>.

<p>* Built from the eight initial variables: MTWeQ, MTDQ, MTWQ, MTCQ, PWeQ, PDQ, PWQ and PCQ. For acronyms see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.t001" target="_blank">Table 1</a>.</p><p>The five MAXENT models for wild-living <i>E</i>. <i>ferus</i>.</p

A Geographic Assessment of the Global Scope for Rewilding with Wild-Living Horses (<i>Equus ferus</i>)

<div><p>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 (<i>Equus ferus</i>) 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 <i>E</i>. <i>ferus</i> populations to climate to estimate climatically suitable areas for wild-living <i>E</i>. <i>ferus</i>. These models were combined with habitat information and past and present distributions of equid species to identify areas suitable for rewilding with <i>E</i>. <i>ferus</i>. 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 <i>E</i>. <i>ferus</i>’ 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.</p></div

Initial set of environmental variables with range values at 10-km resolution for the thinned dataset used for the analysis.

<p>Initial set of environmental variables with range values at 10-km resolution for the thinned dataset used for the analysis.</p

Suitable habitat for wild-living horses (<i>E</i>. <i>ferus</i>) in five major rewilding areas in Europe.

<p>(<b>A</b>) Southern Carpathians. (<b>B</b>) Eastern Carpathians. (<b>C</b>) Velebit. (<b>D</b>) Danube Delta. (<b>E</b>) Western Iberia. (<b>F</b>) Locations of the five areas in Europe (<b>A</b>-<b>E</b>). Colours depict primary habitat (highly suitable land cover), secondary habitat (non-essential land cover occasionally utilised), unsuitable habitat (slopes of 30° or more, closed forest, urban areas, bare areas and cropland) and water.</p

Feral <i>E</i>. <i>ferus</i> in a range of different habitats.

<p>Feral <i>E</i>. <i>ferus</i> inhabit areas worldwide with a wide range of habitats and climates, including Oostvaardersplassen, the Netherlands (<b>A</b>) (Credit: Eva Maria Kintzel and I Van Stokkum); tropical wet and dry seasons in Los Llanos, Venezuela (<b>B</b>) (Credit: Victor Ros Pueo); the Mongolian steppe in Hustai National Park, Mongolia (<b>C</b>) (Credit: Usukhjargal Dorj, Hustai National Park); the deserts of central Australia, western North America and Namibia (<b>D</b>; <b>G</b>; <b>L</b>) (Credit: Pernille J. Naundrup; Bureau of Land Management, USA; Telane Greyling); logged forests and snow covered winters in Alberta, Canada (<b>E-F</b>) (Credit: Bob Henderson); moorlands in Dartmoor, England (<b>H</b>) (Credit: Mark Robinson); feeding in the sand dunes and saltmarshes at Assateague Island, Maryland and Virginia, USA (<b>I-J</b>) (Credit: National Park Services, USA; Fritz Geller-Grimm, CC BY-SA 2.5); and in the mountains of Galicia, Spain (<b>K</b>) (Credit: Victor Ros Pueo).</p

Suitable habitat availability for wild-living <i>E</i>. <i>ferus</i> within five major rewilding areas in Europe.

<p>Suitable habitat availability for wild-living <i>E</i>. <i>ferus</i> within five major rewilding areas in Europe.</p

Analysis of feral horse occurrences using species distribution modelling.

<p>MAXENT species distribution modelling of the selected wild-living horse (<i>E</i>. <i>ferus</i>) localities (n = 76) worldwide using climatic predictor variables. (<b>A</b>) Test gain jackknife evaluation of the relative importance of all variables considered; (<b>B</b>) Test gain jackknife evaluation of the relative importance of the three selected variables; and (<b>C</b>) Estimated response curves (showing the probability of presence using the logistic output from MAXENT). For acronyms, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.t001" target="_blank">Table 1</a>.</p

Potential habitat (suitable land cover) for feral horses (<i>E</i>. <i>ferus</i>).

<p>The distribution of primary habitat within and outside the native range of <i>E</i>. <i>ferus</i> at a 10-km resolution within the extent of the final MAXENT models, showing the primary habitat outside of the native range of <i>E ferus</i> overlapping with the current [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.ref041" target="_blank">41</a>] and Pleistocene distributions of zebras [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.ref041" target="_blank">41</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.ref157" target="_blank">157</a>] in Africa; in areas never inhabited by equids (Australia, New Zealand and Madagascar); outside the native range of <i>E</i>. <i>ferus</i> in areas previously inhabited by equids and outside the current and Pleistocene distribution of zebras (Other). The distribution of <i>E</i>. <i>ferus</i> during the Pleistocene (ca 1.1 MA to 15,000 BC); the Pleistocene/Holocene transition (15.000 to 3500 BC) (modified from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.ref025" target="_blank">25</a>]) and mid/late Holocene (3500 BC-present) are also shown. For maps of past distributions of <i>E</i>. <i>ferus</i>, the distribution of primary habitat and the distribution of other extant equids only, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.s004" target="_blank">S4</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.s005" target="_blank">S5</a> Figs.</p

Areas with suitable climate for wild-living horse populations worldwide.

<p>MAXENT predictions of areas with a suitable climate at a 10-km resolution for models based on (<b>A</b>) mean temperature in the coldest quarter (MTCQ) and precipitation in the driest quarter (PDQ), and (<b>B</b>) MTCQ, PDQ and precipitation in the coldest quarter (PCQ), using the 76 selected wild-living horse (<i>E</i>. <i>ferus</i>) localities. The maps show overlap in the predictions of suitable climates at three presence-absence thresholds: minimum training presence, minimum 10% training presence and equal sensitivity and specificity. The colours indicate the number of threshold criteria predicting a suitable climate for each grid cell ranging from 1–3. (<b>C</b>) Ensemble map showing the overlap of the predicted suitable climates for the two final models for each grid cell, based on the 10% training presence threshold (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132359#pone.0132359.t002" target="_blank">Table 2</a>). (<b>D</b>) Predicted suitable climate from the CEM. Colours indicate the number of overlapping climatic variable ranges for each grid cell, ranging from 1–3.</p

Initial set of environmental variables with range values at 10-km resolution for the thinned dataset used for the analysis.

<p>Initial set of environmental variables with range values at 10-km resolution for the thinned dataset used for the analysis.</p