One of the many possible influences that Beever et al. looked at as part of their study about pika (Ochotona princeps) extirpation in the hydrographic Great Basin area was ungulate grazing. Evident extirpations occurred in seven out of seven instances where grazing took place, compared to only one extirpation out of eleven at ungrazed sites. However, the ungrazed areas were located at higher elevations with a greater amount of habitat nearby and grazed areas were at lower elevations with less talus habitat. Since ungulate grazing within 20-50 meters of pika talus habitat could lead to pikas having to travel further from the talus for forage, foraging-associated costs increase as well as risk of predation. Although competition for the same food source may not occur, ungulate grazing indirectly influences pika habitat through trampling of soils and vegetation. Beever et al. stress that grazing should be incriminated cautiously in connection to pika declines since the talus rock may prevent ungulate and pika interaction; steep terrain and rock formations may stop livestock or horses from assessing pika habitat and keep them grazing in the broader area. Pikas are generalist herbivores while cattle and horses are primarily graminoids, and the diet and behavior of generalist herbivores is tough to model due to nutrient-balancing constraints unrelated to interspecific interactions and variability in plant chemistry. Overall, this study found that current anthropogenic influences, such as grazing, may have combined with other impacts, such as climate and habitat area, leading to pika extirpation in the Great Basin.
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