Yaks in a field. Image credit: Zhong et al. (CC BY-SA 4.0)
On the Qinghai-Tibetan Plateau, yaks share alpine meadows with a small herbivore, the plateau pika. Opinions about the role of pikas are divided. Some see them as serious pests because they compete with yaks for forage and destroy pastureland, causing land degradation and damage to livestock production. Others see them as a keystone species because they play an important role in maintaining ecosystem health as ecosystem engineers and as prey for many predators.
However, no one has ever tested these opposing views. Pikas frequently clip (but do not eat) the tall poisonous weed Stellera. Stellera has expanded massively under grazing pressure, outcompeting palatable grasses and sedges and thereby threatening yak health. Pikas may thus indeed benefit livestock production by removing this poisonous weed.
Zhong et al. wanted to test the hypothesis that at moderate densities, pika may improve yak body growth by suppressing poisonous Stellera plants, but at high densities they may inhibit yak body growth by competing with yaks for food. Using manipulative field experiments, the researchers found that pikas cut down tall Stellera plants, reducing their cover by half. This released grasses and sedges from competition, increasing their abundance and crude protein content by 14%, and improved yak foraging efficiency by 30-40%. Consequently, yak daily weight gain increased by up to 42% in the presence of pikas. Importantly, the relationship was hump-shaped: benefits peaked at ~200 pika burrows per hectare but turned negative above ~400 burrows per hectare.
The study of Zhong et al. shows that moderate pika densities can enhance livestock production by improving forage quality. Local herders and rangeland managers could benefit by moving from an indiscriminate pika eradication strategy to density-based pika management, maintaining pikas at moderate levels (below ~400 burrows/ha) to boost yak growth while preventing outbreaks. However, further research is needed to test whether similar facilitation occurs at higher elevations (>4,000 m), during winter seasons, or with other livestock (e.g., sheep). Achieving these benefits requires adaptive, site-specific monitoring and ecologically based management that integrates livestock production with conservation.
