Environmental change is becoming synchronous across sites with frequent emergence of extremes in recent years, with potential impacts on species’ synchronous abundance over large scales. Analyzing 41 years of breeding bird survey data across North America, we observed that some birds showed mostly lower tail-dependent spatial synchrony (i.e., synchrony across sites at low abundances), while others showed mostly upper tail-dependent spatial synchrony (i.e., synchrony across sites at high abundances). We found that spatial synchrony in climate extremes (i.e., tail-dependence in climate), not the dispersal trait (hand-wing index), drove the spatial synchrony in abundance extremes (i.e., tail-dependence in abundance) up to 250 Km. Tail-dependence in high (or low, respectively) temperature across sites caused lower (or upper, respectively) tail-dependent spatial synchrony in abundance. In a rapidly changing environment, these findings highlight the importance of considering synchronized climatic extremes to assess species’ tail-dependent spatial synchrony across large scales.

A document by Shyamolina Ghosh. Click on the document to view its contents.

Global change alters the stability of biological communities by affecting species richness and how species covary through time (i.e., synchrony). There are few large-scale empirical tests of stability-diversity-synchrony relationships and those mostly focus on the terrestrial realm. Moreover, the effect of synchrony is largely unknown when species only covary at either high or low extremes of abundance (i.e., tail-dependent synchrony), a common phenomenon in ecological communities. Here, we synthesized long-term community time-series data (20+ years of species’ abundances/biomass for 2,668 communities across 7 taxonomic groups) from both terrestrial and freshwater realms and explored how the relationships among richness, synchrony, and stability vary across realms. We also investigated the effect of tail-dependent synchrony on stability across 714 freshwater and 1,954 terrestrial communities. For terrestrial communities, we found a positive diversity-stability relationship and that the tail-dependent synchrony was a more important determinant of stability than the traditional measure of overall synchrony (i.e., based on the covariation of all species). For freshwater communities, only overall synchrony explained some variation in stability. Assessing tail-dependent synchrony can improve our ability to understand why stability varies across different ecosystems and thereby our inferences about the causes of human-mediated biodiversity loss.