This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Small mammals called plateau pikas are often treated as pests because they compete with livestock for food, but research from China shows they can improve the quality of vegetation for grazing yaks. The study is published in eLife.
The findings, based on convincing evidence, provide new insights into reciprocal relationships between small mammals and large herbivores and will interest livestock and rangeland managers. Pikas, voles, prairie dogs, pocket gophers and other small herbivores are both consumers and ecosystem engineers in many grassland areas. Through their feeding, clipping and burrowing behaviors, they profoundly alter vegetation and soil properties, with potential effects on large herbivores that coexist with them.
"In rangelands and other less productive ecosystems, small mammals are often considered pests because their population outbreaks can lead to competition with livestock for food. However, it remains unclear whether their competitive effects on livestock diminish or even help livestock growth when their numbers are at lower, non-outbreak levels," says co-first author Zhiwei Zhong, professor of ecology at the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China. "Livestock grazing currently uses around 77% of global agricultural land and sustains billions of people worldwide.
A critical assessment of small mammals' impacts on livestock production is therefore urgently needed to guide management for both production and biodiversity conservation." For their study, the team assessed how a moderate population density of plateau pikas—as defined by approximately 200 active burrows per hectare—affects yak performance in the alpine ecosystem of the Qinghai–Tibetan Plateau. They hypothesized that, at moderate densities, pikas would improve vegetation for yaks by suppressing tall poisonous plants, or forbs, called Stellera, thereby increasing the abundance and nutritional quality of palatable grasses and sedges during the growing season from June to August. To test these predictions, they first conducted two field surveys to examine how diets differ between pikas and yaks, as well as the associations among pika density, Stellera abundance and yak grazing activity.
They then performed a manipulative field experiment using 150-by-150-meter fenced enclosures on the Qinghai–Tibetan Plateau to test the interactive effects of pikas and Stellera on yak body growth and the underlying mechanisms driving these effects. The field surveys showed that pikas and yaks have distinct diets: Pikas very frequently clipped—but did not eat—Stellera plants and fed mostly on other forbs, while yaks consumed greater proportions of grasses and sedges, as expected. "By selectively clipping tall poisonous Stellera forbs, pikas reduced the cover of these plants by two-thirds, which in turn increased the availability and protein content of grasses and sedges.
By improving the composition of vegetation in this way, the moderate presence of pikas facilitated weight gains in yaks," explains co-first author Bingbo Ni, an environmental researcher at the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences. The team also found that pikas helped improve foraging efficiency in yaks, as measured by the yaks' bite rate (the number of bites taken on plants per hour) and bites–step ratio (the number of bites taken on plants per step). During the manipulative field experiment, when pikas were absent, the team saw that the yaks' sedge bite rate and sedge bites per step decreased by 32% and 46%, respectively, compared with when pikas were present.
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