Cushion plants are foundation species with positive effects extending to higher trophic levels

Abstract

Positive interactions are ubiquitous processes within ecological communities that influence patterns of species diversity and ecosystem functioning. By reducing abiotic stress, such as desiccation, nurse plants positively affect (facilitate) associated plant species. Although plant‐plant interactions are well documented, consequences of plants on higher trophic levels are rarely examined. Here, we test for trophic consequences of the plant community by comparing visitation and diversity of pollinator and arthropod communities between cushion plants and non‐cushion plants throughout the season. Cushion plants were found to have significantly higher visitation rate and diversity of both arthropods and pollinators relative to all other non‐cushion plants. The positive effect of cushion plants found here can be explained for arthropods by cooler and more humid conditions and for pollinators by providing more abundant floral resources throughout the season. Although cushion plants have commonly been reported to facilitate other plants, this study shows that the cushion plant Silene acaulis has a positive effect on plants, arthropods, and pollinators with the greatest positive effect on pollinators. Other cushion plant species are likely also foundation species for many alpine trophic levels and have the capacity to stabilize species diversity at a community level by providing refuges for arthropods and resources for pollinators.