Two new datasets reveal long-term moth community shifts in a biodiversity hotspot

Background/Question/Methods

Insects are declining globally. However, taxonomic and spatial variation in insect decline is poorly understood because long-term insect diversity datasets spanning decades are rare. Using two novel datasets collected by a single observer from the 1980s to the present, we investigated: 1) how moth communities changed over years, 2) whether population trends were mediated by traits, such as wing length and host plant use, and 3) whether changes in moth diversity and communities were driven by climatic variables such as temperature and/or precipitation. Our study focuses in northern California, which is a biodiversity hotspot, within two areas: Davis, CA, a low elevation, suburban community bordered by agricultural land and Stebbins Cold Canyon Nature Preserve, a relatively undeveloped site located at a higher elevation.

Results/Conclusions

Over the study period, more than 400 species of moths were captured in Davis, CA, and over 750 species were captured in Cold Canyon. From the 1980s to the present, population trends varied with taxa, species traits, and sampling location. In the suburban site, pest species were collected more overall than non-pest species, suggesting that local agriculture promotes insect taxa associated with farmlands. For species with negative population trends, declines over time were generally independent of climatic effects, suggesting that other anthropogenic factors, such as pesticide use and/or land development, might be more important than temperature or precipitation for moth fitness in our study region within the timespan of our study. Our data uniquely highlight that moth species are commonly introduced to and extirpated from Northern California.