Dispersal generates a trade-off between adaptive capacity to temperature stress and local adaptation to stable conditions

Background/Question/Methods

In the coming decades, climate change will force biological systems to quickly adapt to a new ecological equilibrium, affecting the basic conditions for provision of ecosystem services and goods. The capacity of local communities to adapt to changing conditions can be fuelled by species sorting, where favorable traits enter the community through immigration. Thus, landscape connectivity is important for adaptive capacity because it regulates the availability of species traits that can rapidly compensate for environmental changes. However, high immigration may also restrict fine tuning of species compositions to local environmental conditions by homogenizing species compositions, and thereby decrease local adaptation. We tested the influence of dispersal on the adaptive capacity to temperature stress, using a model metacommunity system consisting of nine benthic diatom species isolated from the Baltic Sea. The periphyton metacommunities consisted of three habitat patches cultivated at three different light conditions. We ran the experiment for 40 days and manipulated connectivity and temperature in a factorial design: the metacommunities were either connected by manual dispersal or not, and exposed to a field-measured summer heat-wave or a continuous temperature treatment.

Results/Conclusions

Biomass of all metacommunities increased over time, but dispersal had contrasting effects on the rate of increase depending on the different temperature treatments. In the continuous temperature treatment, dispersal promoted a single dominating species in all local patches. In the absence of dispersal, the local patches started to differentiate in community structure depending on the local light climate, and accumulated more biomass than with dispersal. Thus, dispersal decreased local adaptation by preventing differentiation in species composition in response to local environmental conditions. On the contrary, in metacommunities exposed to a realistic summer heat-wave, dispersal promoted recovery by increasing the biomass of heat-tolerant species in all local patches. The heat-wave reorganized the species composition of the metacommunities and after an initial decrease in total biomass by 40 %, dispersal fueled a full recovery of total biomass in the restructured metacommunities. Thus, our results demonstrate that connectivity generates a trade-off between functional optimization and recovery potential, making it difficult to optimize long-term carrying capacity of systems subjected to climate change. However, our results also highlight that connectivity is a key property of the response diversity that allows ecological communities to adapt to climate change through species sorting.