Fig 1.
Feral E. ferus in a range of different habitats.
Feral E. ferus inhabit areas worldwide with a wide range of habitats and climates, including Oostvaardersplassen, the Netherlands (A) (Credit: Eva Maria Kintzel and I Van Stokkum); tropical wet and dry seasons in Los Llanos, Venezuela (B) (Credit: Victor Ros Pueo); the Mongolian steppe in Hustai National Park, Mongolia (C) (Credit: Usukhjargal Dorj, Hustai National Park); the deserts of central Australia, western North America and Namibia (D; G; L) (Credit: Pernille J. Naundrup; Bureau of Land Management, USA; Telane Greyling); logged forests and snow covered winters in Alberta, Canada (E-F) (Credit: Bob Henderson); moorlands in Dartmoor, England (H) (Credit: Mark Robinson); feeding in the sand dunes and saltmarshes at Assateague Island, Maryland and Virginia, USA (I-J) (Credit: National Park Services, USA; Fritz Geller-Grimm, CC BY-SA 2.5); and in the mountains of Galicia, Spain (K) (Credit: Victor Ros Pueo).
Fig 2.
Current distribution of wild-living horses (E. ferus).
The dots indicate the 186 populations of recent wild-living E. ferus identified in this study. Light green, included by the OccurrenceThinner procedure (n = 76); and dark green, excluded (n = 110) (see the text for further details).
Table 1.
Initial set of environmental variables with range values at 10-km resolution for the thinned dataset used for the analysis.
Fig 3.
Analysis of feral horse occurrences using species distribution modelling.
MAXENT species distribution modelling of the selected wild-living horse (E. ferus) localities (n = 76) worldwide using climatic predictor variables. (A) Test gain jackknife evaluation of the relative importance of all variables considered; (B) Test gain jackknife evaluation of the relative importance of the three selected variables; and (C) Estimated response curves (showing the probability of presence using the logistic output from MAXENT). For acronyms, see Table 1.
Table 2.
The five MAXENT models for wild-living E. ferus.
Fig 4.
Boxplots of the three focal climatic variables for wild-living horse (E. ferus) localities (n = 76) worldwide.
Mean temperature in the coldest quarter (MTCQ) (white), precipitation in the driest quarter (PDQ) (light grey) and precipitation in coldest quarter (PCQ) (dark grey). Whiskers mark the 1st and 3rd quartiles, and the line indicates the median. Dots are outliers.
Fig 5.
Areas with suitable climate for wild-living horse populations worldwide.
MAXENT predictions of areas with a suitable climate at a 10-km resolution for models based on (A) mean temperature in the coldest quarter (MTCQ) and precipitation in the driest quarter (PDQ), and (B) MTCQ, PDQ and precipitation in the coldest quarter (PCQ), using the 76 selected wild-living horse (E. ferus) 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. (C) 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 (Table 2). (D) Predicted suitable climate from the CEM. Colours indicate the number of overlapping climatic variable ranges for each grid cell, ranging from 1–3.
Fig 6.
Potential habitat (suitable land cover) for feral horses (E. ferus).
The distribution of primary habitat within and outside the native range of E. ferus at a 10-km resolution within the extent of the final MAXENT models, showing the primary habitat outside of the native range of E ferus overlapping with the current [41] and Pleistocene distributions of zebras [41, 157] in Africa; in areas never inhabited by equids (Australia, New Zealand and Madagascar); outside the native range of E. ferus in areas previously inhabited by equids and outside the current and Pleistocene distribution of zebras (Other). The distribution of E. ferus during the Pleistocene (ca 1.1 MA to 15,000 BC); the Pleistocene/Holocene transition (15.000 to 3500 BC) (modified from [25]) and mid/late Holocene (3500 BC-present) are also shown. For maps of past distributions of E. ferus, the distribution of primary habitat and the distribution of other extant equids only, see S4 and S5 Figs.
Fig 7.
Suitable habitat for wild-living horses (E. ferus) in five major rewilding areas in Europe.
(A) Southern Carpathians. (B) Eastern Carpathians. (C) Velebit. (D) Danube Delta. (E) Western Iberia. (F) Locations of the five areas in Europe (A-E). 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.
Table 3.
Suitable habitat availability for wild-living E. ferus within five major rewilding areas in Europe.