Wild bees are more at risk from climate change-related weather disturbances
Wild bees are under greater threat from than they are from destruction of habitats around the world, according to the authors of the new report Experts from Penn State University studied 14 years of data from wild bee populations in over 1,000 locations in , and Washington . They found that warm winters and long hot summers are reducing the abundance and diversity of plants and flowers - putting ecosystems at risk and making it harder for wild bees - already being wiped out due to pesticides and disease - to survive. Lead author Professor Christina Grozinger said the most critical factor influencing wild bees was the weather - particularly changes to temperature and rainfall. Combating insensitive urban development and intensive farming alone will not be sufficient to protect the vital pollinators, explained Grozinger. In the Northern US, past trends and future predictions show a changing climate with warmer winters, more intense rain in winter and longer growing seasons with higher maximum temperatures, according to Grozinger. 'In almost all of our analyses, these conditions were associated with lower abundance of wild bees,' she explained. This suggests climate change 'poses a significant threat to wild bee communities'. Co-author Melanie Kammerer, a graduate student, said few previous studies have considered the effects of both climate and land use on wild bee populations. 'We thought this was an oversight because, like many organisms, bees are experiencing habitat loss and climate change simultaneously,' Kammerer said. To properly understand the effects of weather and climate - especially with more variable patterns due to climate change - they needed a long-term data set. They examined data from observations of bees in over 1,000 locations over 14 years and looked at both land use and climate change at the same time. Using maps and spatial models, the team described the landscape surrounding each of the sampling spots - like habitat size and available floral and nesting resources. They also compiled a large set of climate variables and used machine-learning, or AI, to identify the most important and quantify their effects on bees. Kammerer said: 'We found temperature and precipitation patterns are very important drivers of wild bee communities in our study - more important than the amount of suitable habitat or floral and nesting resources in the landscape.' Interestingly, different species were most affected by different weather conditions - for example areas with more rain had fewer spring bees. Grozinger explained: 'We think the rain limits the ability of spring bees to collect food for their offspring. 'Similarly, a very hot summer, which might reduce flowering plants, was associated with fewer summer bees the next year.' Grozinger said: 'This result coincides with studies showing that, with earlier spring onset, overwintering adults had higher pre-emergence weight loss and mortality and shorter life span post-emergence.' Ms Kammerer pointed out these weather changes will likely worsen in the coming years, adding that future winters will be warmer and summers hotter. These seasonal changes are predicted to occur more frequently, which 'we expect will be a serious challenge to wild-bee populations,' she said. 'We are just beginning to understand the many ways climate influences bees, but in order to conserve these essential pollinators, we need to figure out when, where and how changing climate disrupts bee life cycles. 'And we need to move from considering single stressors to quantifying multiple, potentially interacting pressures on wild-bee communities.' The study is part of 'Beescape' enabling growers, conservationists and gardeners to explore the landscape quality at their site and make adjustments to improve conditions for bees. Given their latest findings, the researchers plan to expand the project to include weather and climate conditions in future observations. The findings have been published in the journal Global Change Biology.