Do the indirect effects of climate change decrease with species abundance?

Background/Question/Methods

Climate change can affect species directly or indirectly.  Indirect effects occur when climate causes changes in the relative abundances of a species’ competitors. Forecasts of the ecological effects of climate change would benefit from knowing which species are most prone to direct vs. indirect effects. Theory and empirical tests show that indirect effects are likely to be weakest for species that are strongly stabilized by niche differences. Moreover, theory also suggests that large stabilizing niche differences could decrease species’ abundances. We addressed the following questions: 1) Do less abundant species show larger stabilizing niche differences than more abundant species? 2) Does stabilization explain the strength of indirect effects? We built population models of eight interacting species in an Idaho sagebrush steppe. We modeled four abundant species (one shrub and three grasses) and four less abundant species of forbs. We estimated recruitment, survival, and growth as a function of climate and competitor (conspecific and heterospecific) density. We ran four different models, each including the four common species plus one forb, to estimate equilibrium abundances and niche differences. We ran models using observed and perturbed climate and decomposed climate effects into direct and indirect.

Results/Conclusions

As expected, forb species showed larger stabilizing niche differences than common species. Moreover, species with strong stabilizing niche differences also tended to experience small indirect effects. However, there were some exceptions to this latter pattern. This could have occurred in the case not all species in the community had similar proportional responses to climate perturbation. These results have two implications. First, species abundance in plant communities could depend on the strength of stabilizing niche differences. This warrants further investigation, because species rarity is often attributed to low fitness. Second, stabilizing niche differences and abundance could be proxies to identify what species are most affected by indirect climate effects.