Microclimate mediates the strength and direction of avian biotic interactions: a test of the stress-gradient hypothesis

Résumé fourni par la source

The stress-gradient hypothesis posits that species interactions should be competitive in benign environments but tend toward being facilitative in stressful environments. However, this hypothesis has rarely been tested in animal communities. We capitalized on a 13-year, landscape-scale dataset, collected annually in a relatively stable old-growth forest environment to test the long-held hypothesis that the strength and direction of species interactions might be mediated by climatic conditions. It is generally accepted that competitive and facilitative interactions drive the distributions of many species. However, climate-envelope models generally ignore species interactions which may partly explain poor predictive performance of species distribution models in the face of climate change. Using multi-species dynamic occupancy models, we tested whether interannual settlement by one bird species could affect either the persistence or settlement by another phylogenetically related species, and whether these interactions are mediated by microclimate. The high spatiotemporal variability in avian local colonization and extinction dynamics in this landscape affords the opportunity for a rigorous, albeit correlative, natural experimental test of the stress-gradient hypothesis. We found that species interactions were influenced by microclimate for some, but not all avian species pairs. Related species pairs more often showed settlement dynamics that were indicative of attraction rather than repulsion. In some cases, competitive interactions at warmer climates flipped to become attractive interactions in colder microclimates – supporting the stress-gradient hypothesis. However, the reverse was also true: facilitative interactions amplified for some species under warm conditions. Our results highlight the importance of using long-term data to incorporate competitive and facilitative interactions into species distribution models and provide preliminary evidence for the stress-gradient hypothesis in birds.

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