2017 ESA Annual Meeting (August 6 -- 11)

PS 61-172 - Ecosystem engineering strengthens bottom-up and weakens top-down effects via trait-mediated indirect interactions

Thursday, August 10, 2017
Exhibit Hall, Oregon Convention Center
Zhiwei Zhong1, Xiaofei Li1, Dean Pearson2, Deli Wang3, Yu Zhu1 and Ling Wang1, (1)Key Laboratory of Vegetation Ecology, Ministry of Education, School of Life Sciences, School of Environment, Northeast Normal University, Changchun, China, (2)USDA Forest Service, Rocky Mountain Research Station, (3)Key Laboratory of Vegetation Ecology, Ministry of Education, School of Life Sciences, Northeast Normal University, China
Background/Question/Methods

Ecosystem engineering is a powerful force shaping community structure and ecosystem function. Yet, very little is known about the mechanisms by which engineers affect vital ecosystem processes like trophic interactions. Here, we examine the potential for an herbivore ecosystem engineer, domestic sheep, to affect trophic interactions between the web-building spider Argiope bruennichi, its grasshopper prey Euchorthippus spp., and the grasshoppers’ host plant Leymus chinensis.

Results/Conclusions

By integrating small- and large-scale field experiments, we demonstrate that: 1) moderate sheep grazing changed the structure of plant communities by suppressing strongly interacting forbs within a grassland matrix; 2) this change in plant community structure drove interaction modifications between the grasshoppers and their grass host plants and between grasshoppers and their spider predators, and 3) these interaction modifications were entirely mediated by plasticity in grasshopper behavior. Overall, ecosystem engineering by sheep grazing strengthened bottom-up effects and weakened top-down effects via trait-mediated interactions, resulting in a nearly two-fold increase in grasshopper densities. Interestingly, the grasshopper behavioral shifts which reduced spider per capita predation rates in the microcosms did not translate to reduced spider predation rates at the larger system scale because increased grasshopper densities offset behavioral effects at larger scales. Our findings demonstrate that 1) ecosystem engineering can strongly alter trophic interactions, 2) such effects can be driven by cryptic trait-mediated interactions, and 3) the relative importance of trait- versus density effects as measured by microcosm experiments may not reflect the importance of these processes at realistic ecological scales due to scale-dependent interactions.