Forecasting plant community impacts of climate variability and change: when do competitive interactions matter?

1. A change in a climate variable may alter a species abundance not only through a direct effect on that species vital rates, but also through indirect effects mediated by species interactions. While recent work has highlighted cases in which indirect effects overwhelm the direct effects of climate, we lack robust generalizations to predict the strength of indirect effects. 2. For communities dominated by non-trophic interactions, we propose that the potential for indirect effects of climate change declines with the strength of stabilizing niche differences. 3. We tested this hypothesis by analysing an empirically parameterized four species population model. We quantified negative frequency dependence in population growth rates as a measure of stabilizing niche differences and projected the sensitivity of each species to direct and indirect effects of climate perturbations. 4. Consistent with our hypothesis, species' sensitivities to indirect effects decreased rapidly with increasing stabilization by niche differences. 5. Synthesis. Information about niche differences can identify species sensitive to indirect effects of climate change and determine when multispecies forecasting approaches are necessary. However, practical application of this generalization will require methods to predict niche differences from easily collected data.