Linking climate to irruptive dynamics in Californian butterflies

Background/Question/Methods

Irruptive population dynamics have long fascinated ecologists, but analyses have typically focused on a relatively small number of well-studied species, often insect pests of crops. Here we utilize a long-term dataset (more than three decades at 10 sites along an altitudinal gradient) to investigate population dynamics among co-occurring species that represent a continuum of irruptiveness, from relatively stable populations to those experiencing high inter- and intra-annual variation in density. We analyzed these data using a hierarchical Bayesian model to examine the predictive ability of seasonal temperature and precipitation data on explosive butterfly population dynamics. Specifically, we ranked butterflies by population volatility and examined the relationship between rank volatility and weather data to identify associations reflecting the effect of climate variables on taxa across the volatility spectrum.

Results/Conclusions

Despite idiosyncratic, species-specific responses to weather, we also identified several common trends across irruptive species. More volatile species of butterflies were more positively affected by warmer spring temperatures and increased summer precipitation as compared to less volatile butterfly species. Furthermore, while most species exhibited population declines over time (consistent with previous analyses of this fauna), more volatile species were declining less rapidly than less volatile species. Taken together these results suggest that more volatile species are perhaps less sensitive to the myriad changes afflicting California’s butterfly fauna. Our analyses also point towards new directions in the study of irruptive population dynamics.