Demographic Attritions, Elevational Refugia, and the Resilience of Insect Populations to Projected Global Warming

Tropical mountains might protect species from global warming by facilitating biotic migrations upslope. Current predictions of tropical biotic responses to global warming are based on correlations between species elevational distributions and temperatures. Because biotic attritions, range shifts, and mountaintop extinctions result from complex demographic processes, predictive models must be based on mechanistic associations between temperature and fitness. Our study combines long-term temperature records with experimental demography to determine the contribution of local adaptation to organismal resilience in a warming world. On the Barva volcano in Costa Rica, Cephaloleia belti (Coleoptera: Chrysomelidae) displays high-elevation (960-2,100 masl) and low-elevation (50-960 masl) mitochondrial haplotypes. We reared haplotype cohorts at temperatures prevalent along the elevational gradient (i.e., 10 degrees-30 degrees C). Based on ambient temperatures recorded every half hour for 4 years, we projected average instantaneous population growth rates ((r) over bar) at current and future temperatures (i.e., +1 degrees to 6 degrees C) for each beetle haplotype. Haplotypes are adapted to local temperatures, but with a temperature increase beyond 2 degrees C, both haplotypes will face lower-elevation demographic attritions and extinctions. Upper distribution limits serve as potential elevational refugia from global warming. This study shows how species resilience to global warming emerges from complex fitness responses of locally adapted phenotypes facing novel environments.

Automated summary

Tropical mountains may protect species from global warming by facilitating uphill migrations. Research on a Costa Rican volcano found that local temperatures play a significant role in the adaptation of beetles to different elevational habitats, but a temperature increase of over 2 degrees Celsius could lead to demographic reductions and extinctions at lower elevations for both haplotypes. This study highlights how species' resilience to global warming depends on the complex fitness responses of locally adapted phenotypes facing changing environments.