Abstract
Robust predictions of ecosystem responses to climate change are challenging. To achieve such predictions, ecology has extensively relied on the assumption that community states and dynamics are at equilibrium with climate. However, empirical evidence from Quaternary and contemporary data suggest that species communities rarely follow equilibrium dynamics with climate change. This discrepancy between the conceptual foundation of many predictive models and observed community dynamics casts doubts on our ability to successfully predict future community states. Here we used community response diagrams to empirically investigate the occurrence of different classes of disequilibrium responses in plant communities during the Late Quaternary, and bird communities during modern climate warming in North America. We documented a large variability in types of responses, suggesting that equilibrium dynamics are not the most common type of response to climate change. Bird responses appeared less predictable to modern climate warming than plant responses to Late Quaternary climate warming. Furthermore, we showed that baseline climate gradients were a strong predictor of disequilibrium states, while ecological factors such as species’ traits had a substantial, but inconsistent effect on the deviation from equilibrium. We conclude that (1) complex temporal community dynamics including stochastic responses, lags, and alternate states are common; (2) assuming equilibrium dynamics to predict biodiversity responses to future climate changes may lead to unsuccessful predictions
Highlights
Contemporary climate change impacts the dynamics of biodiversity (Parmesan, 2006; Steinbauer et al, 2018) but our ability to predict these impacts remains limited
Anticipatory prediction of biodiversity responses to climate change have considered a limited range of dynamics, relying on predictable relationships between species or community dynamics and climate change
Our work suggests that the current understanding of community dynamics in relation to climate change is oversimplified
Summary
Contemporary climate change impacts the dynamics of biodiversity (Parmesan, 2006; Steinbauer et al, 2018) but our ability to predict these impacts remains limited. The dynamic equilibrium hypothesis assumes that species distributions and Disequilibrium Dynamics and Climate Change assemblages reflect a climate niche optimum in which species climate niches match the observed climate, and that changes in climate induce changes in community composition or species distribution to stay close to this equilibrium state with climate (Webb, 1986; Prentice et al, 1991) This hypothesis assumes a linear relationship between climate and species climate niches, with limited presence of lags, threshold effects, stochastic variations, and transient dynamics in biodiversity responses to climate changes. These processes probably impair the community responses expected from the equilibrium dynamics hypothesis (Jackson and Overpeck, 2000; Krauss et al, 2010). There is growing evidence that biotic responses observed in nature do not match those expected under the assumption of dynamic equilibrium with climate change (e.g., Devictor et al, 2012; Svenning and Sandel, 2013; Ash et al, 2017)
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