Predicting how organisms will respond to anthropogenic climate change and other human impacts on the environment has become a key goal of ecological research, with the ultimate aim of informing conservation management decisions to reduce extinction rates and maintain ecosystem function. Long-term monitoring of organisms has provided evidence that climate change is already impacting ecosystems and that temperature can dictate how species respond to environmental change. Butterflies have generally accelerated their lifecycle as higher temperatures speed up development, expanded their ranges poleward to track optimal climate conditions, and added generations in lengthened growing seasons. However, it is still unknown if these biotic responses to climate change will increase the long-term viability of butterfly species.
This dissertation examines how differences in species’ responses to climatic variability impact population viability using a volunteer-collected, 20-year monitoring data set from the Ohio Lepidopterists. First, I present a new population modeling approach to estimate an abundance index and phenology for separate generations of insects with complex lifecycles. Second, I test what environmental cues induce butterflies to add an extra generation late in the growing season and whether these generations have consequences for population growth rates. Third, I compare annual variation in butterfly phenology with plant phenology, estimated with remote sensing, to analyze if mismatches in phenological responses across trophic levels impact butterfly population growth rates. Finally, I evaluate how species respond to temperature variability across space and time and whether the land cover composition around monitoring sites affects their responses.
Species within the butterfly community demonstrate a diversity of population responses to climatic variability, which could indicate which species will be vulnerable to declines with ongoing anthropogenic climate change. In general, more species have declining statewide population trends than increasing trends. Adding an extra generation, which is an evolved response to photoperiod cues, increases annual population growth rates. Butterfly phenology is less variable than plant phenology and population growth rates are higher when butterfly phenology peaks occurs later in the season. Land-use has little effect on annual population growth rates, which are influenced by density dependence across all species and temperature variability in different ways between species. This dissertation contributes to the understanding of complex insect responses to the direct and indirect effects of climate variability and tests how these responses impact population growth rates, which will determine long-term changes in species’ distributions and abundances.