COS 4-5 - Warming in connected landscapes: an experimental test of metabolic scaling and metacommunity hypotheses for understanding ecological change

Background/Question/Methods

Ecological systems are complex, and experiencing changes associated with warming as well as movement and flows of information, energy and materials. Though we have theories to help us understand ecological change at the community level, in terms of biomass, rank-abundance distributions, biodiversity and productivity, these traditional frameworks have yet to provide a robust understanding of how metabolic scaling and changes to dispersal interact to influence population, community and ecosystem change. We experimental tested the hypothesis that effects of warming on communities are predictable based on metabolic scaling theory for closed ecosystems, and that these predictions change when we account for dispersal of species and phenotypes from other thermal habitats. We used 1000-L cattle tanks to create experimental aquatic communities, and created thermal gradients of four distinct temperatures in sets of four cattle tanks. These were replicated and joined in one of three dispersal treatments. We measured biodiversity among zooplankton and microbiota, and ecosystem fluxes including oxygen and nitrogen fluxes, over a period of 10 weeks.

Results/Conclusions

Warming and dispersal rates interacted to influence community biodiversity and ecosystem function. We found that temperature caused divergence in community composition and biomass, and that productivity and gas fluxes varied with temperature. The degree to which temperature responses aligned with metabolic theory predictions reflected whether the community was open immigration or rescue by taxa from other tanks. Microbiota biodiversity patterns reflected dispersal limitation in the no dispersal tanks, and were more resilient to the thermal gradient in the presence of dispersal. A natural heat wave in the middle of the experiment presented a pulse thermal stress, and connected metacommunities recovered differently than unconnected metacommunities. Overall, our empirical results support predictions from an integrated metabolic scaling biodiversity theory.