Understanding what maintains distributions of closely related species is a primary goal of ecology. Distributions can be determined by abiotic forces such as climate, as well as biotic forces such as species interactions. Recently, species interactions have gained attention as a prominent mechanism that determine distribution limits of closely related species. Long-term data has provided an excellent framework to understand underlying distributions and test how species interactions influence said distributions. In particular, long-term data on trees provide a frame work to test how forest structure and function influences forest biodiversity as a whole. Trees provide structure and resources for a wide range of taxa. While it is broadly understood how abiotic preferences like forest structure shape distributions of closely related species, the influence of species interactions in shaping distributions is poorly understood.
In this study, we are testing how species interactions change across a distribution gradient of closely related species. I hypothesize that microclimatic variability mediates the strength of interactions for closely related species and maintains elevational distributions. To test how species interactions influence distributions I am conducting a playback experiment for three closely related songbird species pairs at the H.J. Andrews Experimental Forest Long Term Ecological Research Station (LTER). The H.J. Andrews encompasses an elevational gradient and has long-term songbird occupancy data that allow us to measure historical distributions. Additionally, the H.J. Andrews has long term microclimate (local scale climate) data which is influenced by forest structure and composition. In the past two years of data collection, we have determined that dominance is predicted by body size and influences the strength of aggression across distributions. Additionally, aggression increases with increasing elevation for two out of three species pairs, suggesting that microclimatic variability or forest type influence the outcomes of species interactions and ultimately distributions. These results provide preliminary evidence that species interactions influence distributions and may be mediated by climate. Trees are critical in shaping bird distributions as they provide structure and shape forest microclimate. Forest microclimate, is influenced by forest structure and influences bird distributions. This study incorporates how biotic interactions may mediate responses to climate in shaping distributions and provides a framework of how long-term tree plots can be used to study a wide range of forest species. This work also has implications for climate change as closely related species will track their preferred climatic conditions, causing novel species interactions.