PS 17-237 - Pollinator communities of California’s central coast: from past to present

Abstract: Insects are the largest and most diverse group of animals on the planet, and serve critical functional roles in ecosystems including pollination. Insects are in alarming decline, impacted by anthropogenic disturbance at regional and global scales. Because insect response to anthropogenic disturbance can be idiosyncratic, it is important to study pollinator dynamics on a local scale particularly in species rich ecosystems with potentially complex species relationships. This study measured changes in pollinating bee and fly richness and community composition in Central California’s coastal dune and scrub ecosystem between the 1990s and present day. We compared modern-day bee and fly pollinator richness and community composition to an extensive unpublished dataset collected by naturalist Randall Morgan in the 1990s. In the subsequent three decades sites were fragmented, however our study did not assess these changes. We resampled historical sites using aerial nets to collect all bee and fly daytime pollinators on flowering plants. We found no change in pollinator richness over three decades, but significant shifts in community composition. Both bee and fly community composition shifted with multiple species gained and lost over the 30 year time period. In conclusion, this study shows that traditional metrics of biodiversity, like species richness, may provide an unclear assessment of changes in pollinator communities noting the considerable changes in species composition but not diversity over the three decades. This study also shows the value of how historical datasets from museum collections and community members can be used to examine long-term changes in biodiversity.