Historical distribution, habitat requirements and feeding ecology of the genus Equus (Perissodactyla)

Dietary traits of nine extant Equus species (E.africanus, E.ferus, E.grevyi, E.hartmannae, E.hemionus, E.khur, E.kiang, E.quagga and E.zebra) were reconstructed and ranked in a continuum reflecting the relative proportions of abrasion and attrition. In order to match them automatically with climatic data, localities were referenced within a 2 degrees worldwide grid system using geographical information system software. The mesowear score was used as a proxy variable to test the covariance of diet with mean annual precipitation, evapotranspiration, mean annual climatic water balance and mean annual temperature. Seven of the nine equid species presented mesowear signatures indicating a grass-dominated diet, and we found interspecific as well as intraspecific variability. Non-gramineous food components shifted the equilibrium towards the attrition-dominated end in E.africanus and E.khur, indicating an intermediate diet. Especially in E.zebra, additional sources of exogenous abrasives (grit and soil) might increase dietary abrasiveness. In E.quagga, dietary flexibility and the capability to cope with increased abrasiveness are considered keystone factors allowing its large geographical range. The broad, species-specific range of climate parameters associated with the habitats was used to define the thresholds of the species' feeding niches. Our data suggest that climate as represented by the variables we used does not, in the first instance, relate to the tooth wear signature of equids. We thus conclude that the tooth wear signature is more specific to the feeding strategy and should be regarded a dietary trait rather than an immediate imprint of climate. However, tooth wear can be used to infer local dietary traits and might therefore become an important tool in conservation management.