Assessing the current status and projecting future changes in biodiversity under scenarios that consider multiple global change drivers is critically important for resource planning and management. To create fine-grain, nationwide projections of changes in biodiversity relevant to planning and decision-making, we need to first understand how processes that limit the number species in a region (available energy and physiography) and processes that selectively add or remove species from a region (anthropogenic changes to the landscape) interact to regulate current levels of biodiversity. Global changes to the environment will alter both the energetic capacity of ecosystem to support biodiversity as well as the degree to which anthropogenic drivers modify that capacity, thus both must be accounted for in future projections.
Borrowing methods from economics, we used frontier analysis to analyze spatially explicit measures of available energy and physiography with North American Breeding Bird Survey data collected between 2010 and 2014. Frontier models estimated the potential capacity of ecosystems to support avian diversity at more than 1,500 locations within four ecoregions of the conterminous USA. Within each ecoregion, we evaluated the degree to which a suite of anthropogenic drivers explain deviation of observed estimates from potential avian diversity derived from frontier estimates.
Results/Conclusions
Ecoregions in the conterminous USA differed significantly in estimates of avian abundance (F = 80.48, p < 0.001) and richness (F = 139.84, p < 0.001) with abundance highest in the Great Plains, and richness highest in Eastern Forests. Abundance and richness were both lowest in the Intermountain West. Similarly, frontier models identified that ecoregions differed in the degree to which climatic (e.g., humidity, temperature and precipitation) and physiographic constraints influenced the potential capacity to support avian diversity and the relative importance of anthropogenic factors (e.g., land use, population density, sound and light pollution) for determining observed estimates of avian diversity. Understanding the relationship between potential and observed diversity in current ecosystems is a critical step towards understanding how to accurately integrate climate, land use, and human population projections to develop predictive outcomes of how biodiversity is expected to respond to changes in climate and anthropogenic disturbance across the coterminous United States in the coming decades.