A hallmark of the Anthropocene may be increasing frequency and scale of regime shifts, caused by human domination of ecological processes and the erosion of resilience in many systems. Therefore, it is increasingly necessary to quantify ecological resilience, and changes therein, to inform policy and prioritize management. Traditional metrics for estimating ecological stability and sustainability (e.g., species richness) have been unable to detect how resilient ecological systems are to change. Discontinuity analysis has recently emerged as a robust metric for quantifying ecological resilience in both social and ecological communities, to assess functionality across scales, and as an early warning indicator. We provide the first comparison of the ability of resilience metrics versus traditional metrics for assessing relative ecological resilience and vulnerability to ecological change. Using the North American Breeding Bird Survey, a long-standing, continental-scale annual survey of breeding birds in North America, we compared the ability of traditional ecological stability metric (species richness) to resilience metrics (e.g., number of discontinuities in bird community body mass, functional diversity and redundancy within and across scales) to track community stability and change (i.e., species turnover) across North American ecoregions.
Resilience metrics correlated more strongly with community stability and change than species richness. Number of discontinuities and functional redundancy strongly negatively correlated with species turnover. Cross-scale functional diversity had similar, but weaker, relationships with turnover. Species richness also correlated negatively with turnover, but weakly and with a temporal lag. Overall, ecoregions with higher resilience metrics (i.e. many body mass aggregations, high functional diversity and redundancy, high species richness) experienced less variability in community structure, lower magnitudes of species turnover, and retained more similar cross-scale structure over time than ecoregions with lower resilience. Our study demonstrates the ability of discontinuities and cross-scale functional structure metrics to provide comparable estimates of resilience within and across complex systems. With the current era of global ecological change and surprise, the ability to quantify the relative resilience of ecological systems to disturbance will allow land managers and policymakers to prioritize management efforts to systems with lower relative resilience. We discuss how quantifying relative differences in resilience among ecoregions can enhance estimates of vulnerability to ecological and anthropogenic disturbance.