Resurveying historically sampled sites to understand wild bee population trajectories

Evaluating wild bee species’ population trajectories is essential for their conservation. However, due to funding and personnel turnover, it can be hard to capture more than a brief snapshot in time, with only a few years’ worth of surveying effort. These short studies limit our ability to assess species statuses, as we cannot determine long-term population trajectories. Here, I’ll discuss three studies, from very different landscapes, where we leveraged data from previous studies to better understand species and community level changes over time. On highbush blueberry farms in Michigan, we resampled 15 sites in 2017 and 2018 that had been previously sampled over two different time periods (2004-2006 and 2013-2014). We detected a significant decline in wild bee abundance in the middle sampling period (2013/2014) followed by a rebound in many species’ abundances, though not all. At a nature preserve in Michigan, we analyzed almost a century of bee records to reveal a unimodal peak in wild bee abundance in the 1970s followed by a steady decline in abundance and significant change in the bee community composition. Finally, in the Mojave desert, we returned to sites initially surveyed in 1995 for the Mojave poppy bee, Perdita meconis, and more recently surveyed in 2020-2024. This bee is currently being considered for listing under the Endangered Species Act, and we found large year to year fluctuations in presence. These studies highlight the importance of long-term data availability and returning to sites with previous survey efforts.