SYMP 5-1 - CANCELLED - Non-equilibrium is the norm: Theory-data integration to predict community responses to global change

Background/Question/Methods
Increasing global change has emphasized our need to understand non-equilibrium ecosystems, leading to two critical tasks for community ecology: (1) creating general, cross-system theories for predicting the response of complex ecological communities to global change and (2) translating theory into system-specific predictions through data-model integration. We argue that predicting community change will require novel theory development for non-equilibrium systems coupled with long-term experimental manipulations and an open-science philosophy. A close dialog between theory and empirical approaches is necessary as we aim to understand underlying mechanisms of community dynamics, update theory based on observed patterns, and use theory to translate experimental results across systems. Here, we present multiple vignettes integrating non-equilibrial theory and experiments with the aim of understanding community response to global change. First, we use a globally-replicated nutrient addition experimental to test prediction of a stochastic population model, examining transience and lagged-extinction events to global change. Then, we scale species-level patterns to examine community synchrony, stability, and community assembly under global change, both theoretically and across two long-term experimental manipulations, ranging from nutrient deposition in grasslands (Cedar Creek, MN) to warming and snowpack changes in the alpine (Niwot Ridge, CO).

Results/Conclusions
In plant populations experiencing global change (here, chronic nutrient addition), we found that population size contributed strongly to short-term extinction risk, as expected from stochastic population theory. However, long-term extinction risk depended less on population size, deviating from classic stochastic models when we consider global change and transient dynamics. Extending these analyses to examine community patterns in synchrony, our theoretical model predicted increased synchrony with global change, as environmental conditions passed thresholds where species responded similarly to environmental drivers. However, in a multidecadal grassland experiment (Cedar Creek, MN) we found the opposite pattern as predicted—chronic nutrient addition instead led to increased compensation, where species fluctuations became more negatively correlated. Similarly, in an alpine plant community (Niwot Ridge, CO), we found that warming caused strong reshuffling in competitive hierarchies, a mechanism recently shown to increase compensation. These juxtapositions between theoretical predictions and experimental patterns arose from shifts in the local species pool, while our original model only considered changes in abundances of the historic community. These discrepancies highlight the need to consider both regional and local dynamics in non-equilibrium theory and demonstrate the power of integrating theory and long-term, cross-system experiments to predicting community responses to global change.