Climate change forces species to track changing climates. To date, most research has centered on understanding how climate change will shape new ranges by affecting abiotic components of the fundamental niche. Yet, we know that species interactions also can affect species ranges by affecting the realized niche. Climate change can alter species interactions and biotic range limits by directly modifying species interactions (e.g., temperature-dependent competition) or by altering range overlaps. This latter effect occurs if range boundaries change independently because species track climate changes differently. Changing range boundaries can lead to novel ‘non-analogue’ communities and break apart obligate relationships among coevolved organisms. Here, I develop a model to assess how competition modifies community responses to climate change along a climate gradient. I evaluate how temperature-dependent competition and interspecific variation in dispersal affect extinction risk and diversity patterns.
Results/Conclusions
Competition substantially slowed climate tracking by decreasing fitness and also because competitors directly impeded species from tracking their optimal climates. Climate change altered diversity the most when species had narrow niches, when mean community-wide dispersal rates were moderate, and most substantially, when species differed in dispersal abilities. With high interspecific dispersal variance, the best dispersers tracked climate change, outcompeted slower dispersers, and caused their extinction. Our results show that communities of species with narrow niches (e.g., tropics) and with high variance in dispersal (most communities) will be most threatened by climate change. Current forecasts likely vastly underestimate climate change impacts on biodiversity by neglecting the joint impacts of species interactions and dispersal differences. Future work needs to incorporate species interactions of all types and differences among species.