Image above: wild sandy bee

Over the past thirty years, expanding agricultural development and climate change have been responsible for an increase in disturbed bee habitats and a 94 percent loss of plant-pollinator networks in northeastern North America, according to a study by York University researchers.

These researchers in collaboration with corresponding author Professor Sandra Rehan of the Faculty of Science and grad student Minna Mathiasson of the University of New Hampshire undertook a study of plant-pollinator networks from 125 years ago through present day.

Such networks are composed of wild bees and the native plants they historically rely on for food and pollination, but most of these have been disrupted now.

In 64 percent of the network loss, the association between the wild bees and the native plants is gone. Although the native plants still exist, like willow and sumac, or the wild bees still exist in the area, such as miner or sweat bees, those bees do not visit those plants any longer.

Roughly 30 percent of the plant-pollinator networks are completely lost. In these cases, either the bees, the plants or both have completely disappeared.

Only about 6% of the plant-pollinator networks are stable or thriving. For instance, small carpenter bees like to make their nests in broken stems.

Watch Dr. Sandra Rehan in this 14:04-minute TedX Talks presentation about The Secret Lives of Native Bees:



According to Rehan, there are several reasons these networks are being lost. Climate change is the biggest reason. There has been a two and a half degree change in annual temperatures over the past 100 years and this impacts when certain native plants bloom.

For bees that are only out foraging for a couple of weeks a year, with only a few floral hosts, this could have devastating consequences. In contrast, for bees with longer foraging times of several months that are also generalist pollinators, this would not create as much of a critical mismatch.  

Another contributing factor to the decline of the networks is the increase of invasive plant species and non-native bee species. These usually come into circulation by accident through ornamental plants or through trade and have displaced some native species.

Many such bees live in plant stems, so it is easy to unknowingly import plants with non-native bees in them. In fact, Rehan can show some ways and routes of invasion biology. These bees travel along shipping routes from one continent to another and can travel worldwide. They land in North America in ornamental plants that we buy for our gardens.

It is critical that we increase habitat restoration and the planting of native flowering plants in agricultural landscapes, according to the researchers, as this will improve wild bee biodiversity and provide more food security for humanity.

The “bee business” and other pollinators are worth hundreds of billions of dollars globally. They pollinate crops that we eat. Wild bees top the list and are believed to pollinate over 87% or 308,006 flowering plant species. Apples and blueberries are examples of some of the economically important commercial crops they pollinate.

Rehan reminds us that there is an urgent need for us to understand on a deep level the environmental circumstances that are affecting the wild pollinator populations, as well as their specialized relationships with plant communities and how it is all evolving. Changes in the landscape affect the plant-pollinator webs, which depend on the land. Each regional habitat should be understood locally, and how the networks are shaped.

Rehan and the team previously researched 119 wild bee species over a 125-year period and found 15 declining and 8 increasing species. All the wild bee species in decline are native, and over half of them experienced significant range shifts, like latitude and elevation.

The original study results from York University in Canada can be read here