Long-term monitoring of changes in the native bumblebee community after alien species (Bombus terrestris) invasion and estimation of factors affecting its abundance

Invasive alien species can negatively affect native species communities. Bombus terrestris , an invasive species, has become dominant among bumblebee communities in many areas worldwide. In 2007, B. terrestris invaded the Notsuke Peninsula, a critical area for biodiversity conservation on the northern island of Hokkaido, Japan. We surveyed native bumblebee species across the peninsula from 2007 to 2019 and identified changes in the native bumblebee community using non-metric multidimensional scaling. We also surveyed B. terrestris and estimated the factors influencing its population using a zero-inflated Poisson regression model. A few years after the invasion, B. terrestris was observed across the peninsula, except at the southwestern end. However, its abundance did not increase, as in the other areas of Hokkaido. Analytical results showed a significant association between the change in the native bumblebee community and B. terrestris abundance and positive relationship of B. terrestris abundance with temperatures. As the annual temperature increased, observation of B. terrestris also increased; however, the species has not become dominant on the Notsuke Peninsula. Bombus terrestris favors a relatively warmer climate in its native areas and requires high temperatures for colony development; thus, it may not adapt well to the current cold climate of the Notsuke Peninsula. The climate could affect the population growth of B. terrestris directly through physiological traits, such as behavior, survival, and reproduction, as well as indirectly through the availability and composition of floral resources. Therefore, long-term monitoring for risks to the bumblebee community in future climate change is important for management.