Food and habitat provisions jointly determine competitive and facilitative interactions among distantly related herbivores

• Published in: Functional ecology 2019-12, Vol.33 (12), p.2381-2390
• Main Authors: Pan, Duofeng, Li, Xincheng, De, Kejia, Wang, Ling, Wang, Deli, Guo, Qinfeng, Gao, Chao, Zhong, Zhiwei, Zhu, Hui, Shen, Zhongbao, Seastedt, Timothy R., McArthur, Clare
• Format: Article
• Language: English
• Subjects: Animal bites; Bos grunniens; Caterpillars; Competition; Diet; diet preference; Environmental changes; facilitation; Food; Food availability; Food resources; Foraging behavior; Foraging habitats; forb; Forbs; Gynaephora; Habitat improvement; Habitats; Herbivores; Insects; Kobresia pygmaea; Ovis aries tibetica; Sheep; Terrestrial environments; Vertebrates
• ISSN: 0269-8463; 1365-2435
• DOI: 10.1111/1365-2435.13456

Interactions between distantly related herbivores exert powerful influences on ecosystems, but most studies to date have only considered unidirectional effects. Few have simultaneously examined the mutual effects that vertebrate herbivores and insect herbivores have on one another. We conducted a set of manipulative experiments to evaluate the potential competition and facilitation between two pairs of distantly related herbivore taxa: an insect caterpillar (Gynaephora alpherakii) and two large vertebrate herbivores, yak (Bos grunniens) and Tibetan sheep (Ovis aries tibetica). We found that these large herbivores consistently increased the density of caterpillars likely by improving the habitat for caterpillars. The caterpillars, in turn, decreased yak but increased Tibetan sheep foraging time and intake bites by differently changing available food resources of the two large herbivores. Diet preferences of herbivores modified the habitat and food resources, thereby causing a diet‐mediated competition between yak and caterpillars, and facilitation between sheep and caterpillars. The vertebrate herbivores non‐feeding upon Lamiophlomis rotata and Gentiana straminea, the caterpillars preferred habitat, increased densities of the two plant species, thus favouring the caterpillars. In turn, the caterpillar preference for Kobresia pygmaea significantly reduced food resources for yak, while promoting food resources (multiple forbs) for sheep. Synthesis. Our study indicates that two different mechanisms (the changes in habitat and food availability) induced by herbivore foraging jointly determine competitive and facilitative interactions between distantly related herbivore species. We also suggest that examining the bi‐directional effects between herbivores offers a better understanding of competition and facilitation in terrestrial animal communities. 摘要 食草动物之间的相互作用关系在自然界中十分普遍。但是，当前的大多数研究只关注了食草动物之间的单向作用，关于大型脊椎与小型非脊椎食草动物之间的双向互作关系也鲜有报道。 本研究通过野外放牧实验及昆虫去除实验，探讨了青藏高原高寒草甸生态系统中大型食草动物（牦牛Bos grunniens、藏绵羊Ovis aries）与草原毛虫（Gynaephora alpherakii）之间的互作关系及其潜在的发生机制。 牦牛与藏绵羊均可以通过改善草原毛虫的生境，间接促进毛虫的种群密度。但是，草原毛虫对两者的作用效应相反：草原毛虫降低了牦牛在同域植物斑块内的采食口数和采食时间，但增加了藏绵羊的采食口数和采食时间。这种作用效应的差异是由于草原毛虫的采食作用对牦牛和藏绵羊各自食物资源（植物）的影响不同导致。在本研究中，食草动物的偏食性是调节种间关系的重要因素。牦牛和藏绵羊均不喜食草原毛虫的主要寄居植物（独一味Lamiophlomis rotata和麻花艽Gentiana straminea），其采食作用间接增加了这两种植物的密度，因而为草原毛虫提供了更多的庇护所生境，对其产生促进作用；草原毛虫和牦牛均喜食高山嵩草（Kobresia pygmaea），因而两者间存在食物资源的竞争关系；而草原毛虫对高山嵩草的偏食则间接有利于藏绵羊喜食的杂类草的生长和扩张，从而对后者的采食活动产生促进作用。 本研究表明，生境和可利用食物资源的变化是调节多种食草动物共存的关键