Mammalian herbivores reinforce ecological state transitions in the Chihuahuan Desert
Shrub encroachment is a driver of landscape change in drylands globally. In the Chihuahuan Desert, past livestock overgrazing interacted with prolonged drought to convert vast expanses of black grama (Bouteloua eriopoda) grasslands to honey mesquite (Prosopis glandulosa) shrublands. The potential for wild herbivores to trigger or reinforce shrubland states is underappreciated, however, and few studies compare herbivory effects across multiple consumer taxa. My aim was to clarify how domestic cattle, exotic African oryx (Oryx gazella), and native herbivores contribute to loss of arid grasslands. Native rodents and lagomorphs were especially important in determining grass cover and plant species composition in wet periods and affected perennial grass persistence over multiple life stages. Conversely, during drought, climate drove declines in perennial grass cover, promoting shrub expansion across landscapes. In that shrub-encroached stage, native small mammals reinforced grass loss in part because habitat structure provided cover from predators.
