Moth diversity and body size trends along an elevational gradient: Insights into the effects of climate change

Background/Question/Methods

Moths are a critical food source for birds and other vertebrates and there is growing understanding of their importance as pollinators in both natural and agricultural systems. Like other groups of insects, moths are declining globally due to habitat loss, climate change, and other stressors. Elevational gradients, which encompass variation in temperature and precipitation, can be used in space-for-time substitutions to investigate how insects will respond to climate change. Previous studies show that elevational trends in moth diversity and body size are spatially and taxonomically heterogeneous, and our understanding will benefit from additional studies in different systems. Using specimens collected along a steep elevational gradient in Southern California, we ask how does (1) moth diversity and (2) moth body size vary with elevation? From February-July, and during two consecutive years (2020 and 2021), moth communities were sampled monthly with light traps at five different elevations (210, 828, 1289, 1967, and 2450 m). Each specimen was identified to family and morphospecies, and classified as small, medium, or large. We tested the effects of elevation on species richness, abundance, and Shannon diversity using ANOVA. We used Chi-squared tests to test the expectancy of moth body sizes at each elevation.

Results/Conclusions

Preliminary analyses reveal no significant trends for Shannon diversity (t = 1.745, p = 0.124, R2 = 0.3032). Analyzed separately, the dominant family (Noctuidae) shows an increase in both species richness (t = 13.88, p = 0.00081, R2 = 0.98), and abundance (t = 2.90, p = 0.023, R2 = 0.54) with increasing elevation. Observed moth body sizes deviated significantly from expected (X2 = 39.411, df = 8, p-value = 4.123e-06). There were significantly more small moths than expected at lower elevations, and significantly more large moths than expected at higher elevations. Previous studies suggest that thermoregulation is a possible mechanism driving elevational trends in moth body size. At higher elevations and lower temperatures, smaller insects are unable to elevate their thoracic temperatures above the operative environmental temperature. Our results advance the understanding of how moth diversity and size varies in relation to climatic factors, which will help inform predictions about how moths will respond to future climate change. Based on our preliminary results, we predict that as temperatures rise, Noctuidae diversity will decrease, and that moth body size will decrease across families. As moths are herbivores, pollinators, and prey, these changes could have cascading effects on ecosystem function.