Climate-mediated changes in community composition have been documented across a multitude of taxa; from vegetative communities to higher-level trophic species. Altering community composition may lead to novel species assemblages, changes in species interaction strengths, and altered ecosystem dynamics, ultimately impacting ecosystem functionality and persistence. Across the Gulf of Mexico (GoM) reductions in severity and duration of winter freezes have facilitated the expansion of mangroves into previously salt marsh dominated habitat. Using birds as model taxa, we investigated the impacts of climate-mediated shifts in foundational species on multiple facets of avian biodiversity. Utilizing a long-term, standardized avian monitoring data set (e.g. U.S. Geological Survey Breeding Bird Survey) paired with environmental variables, we investigated how climate change and associated land cover change impacts avian communities along coastal sites throughout the GoM and eastern portion of Florida from 1980-2016. Specifically, we were interested in testing whether the transition from herbaceous to woody wetland and increases in intensity of climatic extremes (i.e. temperature anomalies) drive shifts in bird species richness (alpha diversity) or elevated rates of bird community turnover through time (temporal beta diversity).
Results/Conclusions
Across the GoM, average, site-scale alpha and temporal beta diversity of wetland bird communities have increased since 1980. There was a negative correlation between alpha and temporal beta diversity across sites, however, suggesting that community turnover was largely not driven by increases in the number of species at a site. The was a positive relationship between the intensity of temperature anomalies and temporal beta diversity indicting bird communities at sites that experienced the most extreme heat events were changing the fastest. Conversely, changes in alpha diversity were best explained by increases in precipitation anomalies. Surprisingly, percent change in mangrove cover and precipitation were not strong predictors of temporal beta diversity. Through these initial analyses we documented significant changes in both the richness and composition of wetland bird communities at large spatial scales over the last four decades. Climatic drivers were stronger predictors of temporal trends in avian diversity than habitat cover variables at the regional scale. Future work will investigate whether changes in richness and community composition are driven by poleward shifts in species distributions and how species traits mediate observed responses to changing climate.