Species with more volatile population dynamics are differentially impacted by weather

Abstract

Climatic variation has been invoked as an explanation of population dynamics for a variety of taxa. Much work investigating the link between climatic forcings and population fluctuation uses single-taxon case studies. Here, we conduct comparative analyses of a multi-decadal dataset describing population dynamics of 50 co-occurring butterfly species at 10 sites in Northern California. Specifically, we explore the potential commonality of response to weather among species that encompass a gradient of population dynamics via a hierarchical Bayesian modelling framework. Results of this analysis demonstrate that certain weather conditions impact volatile, or irruptive, species differently as compared with relatively stable species. Notably, precipitation-related variables, including indices of the El Niñ o Southern Oscillation, have a more pronounced impact on the most volatile species. We hypothesize that these variables influence vegetation resource availability, and thus indirectly influence population dynamics of volatile taxa. As one of the first studies to show a common influence of weather among taxa with similar population dynamics, the results presented here suggest new lines of research in the field of biotic-abiotic interactions.

Understanding a migratory species in a changing world: climatic effects and demographic declines in the western monarch revealed by four decades of intensive monitoring

“…And, to what extent can fluctuations in observed monarchs per year at focal sites be predicted by local and regional weather variables, both at the summer sites and at the overwintering grounds? With respect to these questions, we predict monarch numbers to be declining, as previous studies have shown negative trends over time for most butterflies in the region, especially at low-elevation sites (Forister et al 2011;Harrison et al 2015). We also hypothesize that warming conditions will have had a negative influence on the population, as has been observed for other butterflies in northern California (Casner et al 2014).…”

“…This analytical method is described in detail elsewhere (see Nice et al 2014;Harrison et al 2015). Briefly, the model estimates posterior probability distributions (PPDs) for partial regression coefficients associated with model terms at multiple hierarchical levels, in this case site and transect wide.…”

Increasing neonicotinoid use and the declining butterfly fauna of lowland California

“…In order to investigate species-specific sensitivities to neonicotinoids, we used a hierarchical Bayesian binomial regression that estimates population-level beta coefficients, as described in detail elsewhere [13,14]. The model included annual neonicotinoid totals (kilograms) for each county, as well as year, with the response variable being the number of days butterflies were observed (for each species) out of the total number of days that each site was visited.…”

Impacts of a millennium drought on butterfly faunal dynamics

“…Previous analyses of abiotic effects have noted responses to weather that were heterogeneous and idiosyncratic among sites and species [16,17]. For example, associations with climatic variables often differ in sign among congeneric species [18], and even among populations of a single species [17].…”