Professor University of California Davis, United States
Abstract: A rapidly warming climate has become one of the primary forces driving changes in biodiversity worldwide. The impact of warming temperatures on insect communities is of particular interest given this class’s importance for ecosystem function and service provision and the uncertainty around whether insect communities can keep pace with the rapidity of increasing temperatures. Among bumble bees, a well-studied and important group of pollinators, the impact of climate change relative to other, ongoing anthropogenic factors is subject to debate given methodological approaches and the complexities of using imperfect historical records. Using a long-term dataset on bumble bee species occurrence and summer maximum temperature trends across North America, we characterize bumble bee responses to recent climate warming at a community level by examining changes in the community temperature index (CTI) – a measure of the balance of cool- and warm-adapted species within local communities. Starting in 2010, bumble bee CTI has rapidly increased after a period of slight increase from 1989 to the late 2000s. This increase is strongly associated with recent increases in maximum summer temperatures. The increase in CTI is spatially extensive, occurring throughout North America, but greatest at higher latitudes and elevations. On average, bumble bee CTI has increased 0.99°C from 1989 to 2018, a change of similar magnitude to the increase in maximum summer temperatures. Even though this indicates a rapid shift in bumble bee communities, advances in temperature are outpacing bumble bee species capacity to track suitable conditions. Other global change drivers are also likely at play, however our results provide strong evidence of the pervasive impacts posed by unprecedented temperature increases.
