Reconstructing butterfly-pollen interaction networks through periods of anthropogenic drought in the Great Basin (USA) over the past century

Abstract

Interactions between plants and insects dominate terrestrial biomes and are altered in response to global human-environmental change. Documenting such changes in complex interactions is challenging, however, because traditional methods for describing plant-insect interactions at community scales are often based on relatively short sampling periods. This paper investigates quantitative networks of pollen-insect interactions gleaned from adult Lepidoptera from long-term museum collections that helped to overcome the challenge of limited temporal resolution. The paper reports how richness and frequency of butterfly-pollen associations have changed over a 100-year time series (1910–2020) in the Great Basin of Nevada and California, USA. First, we examined changes in pollen richness for 19 butterfly species over five consecutive 20-year time periods. We pooled interaction networks associated with specimens captured before and after the onset of drought in 2000. In doing so, we estimated variation in pollen-pollinator interactions under anthropogenic drought periods in the Great Basin in the last two decades. Overall, pollen richness associated with butterflies declined slightly over the study period. The details depend on the species, however, where a few species experienced moderate declines in richness and two species exhibited small increases in pollen richness. Butterfly-pollen networks indicated specialization in most pollen-butterfly species interactions. They are apparently more reticulate than observational networks. Interaction networks associated with specimens captured before and after the year 2000 revealed that, compared to previous decades, butterfly-pollen networks over the past 20 years had higher connectivity and diversity of interactions. • Plant-pollinator interactions contribute substantially to biodiversity. • Moderately generalized networks are likely to provide ecosystem stability in the face of anthropogenic global change. • Pollen-butterfly interactions are changing in response to global change, especially more generalized interactions. • Most pollen-butterfly interaction networks are specialized, which could make them more susceptible to anthropogenic change. • Pollen diversity on Great Basin butterflies has declined over the past 100 years, concurrent with drought in the region.