(CN) — North American butterflies and bees are on the decline, spelling trouble for the continent’s healthy ecosystems and food security amid climate change and ever-changing land use policies, researchers said in a study Wednesday.

The findings published by PLOS ONE come from a team of researchers who set out to understand the broader geographic trends of pollinator diversity and declines in North America over the last century. To do so, the researchers assessed the current state of pollinators in Canada, the U.S. and Mexico by examining the spatial and temporal records of key pollinator families, known and potential pollinator genera and more well-known pollinator species of concern.

“The agreement between analyses performed at multiple taxonomic levels across all three parts of our study provides evidence that records of pollinators in at least four key groups (Apidae, Megachilidae, Pieridae and Papilionidae) have experienced disproportionate increases in the eastern and southeastern U.S. relative to the western U.S. and southern Mexico,” the authors write in the study.

When pinpointing geographic areas of vulnerability, the researchers also found that many species of conservation concern were concentrated around the Great Lakes region, southern Canada and throughout the east coast of the U.S.

“Where more sampling is performed, it is more likely that managers and researchers will detect declines over time and thus determine that a species is of concern, and it is also more likely that rare species will be detected,” the authors write. “At the same time, areas of high human activity are likely to exhibit high habitat loss and other environmental change, with impact to pollinator populations.”

The results, the researchers say, underscore the need for more studies to identify declining populations for conservation efforts — especially when over 85% of the world’s flowering plants, including crops, need pollinators to maximize reproductive output.

“In spite of data gaps and biases, our results hold implications for policy and management,” the authors explained, adding that western U.S. territories once abundant with pollinators have been substantially altered by decades of fire suppression, overgrazing, recreation and resource extraction.

“In southern Mexico, where SDMs also indicate decreased species richness, expansion of pasture and tree plantations have resulted in losses of native forest since the turn of the century,” the authors write. “These known environmental changes may help explain the pollinator range shifts and losses we detected here.”

One encouraging finding of the study is that some pollinators remain abundant in several developed and urban areas. That outcome, the authors say, is made possible with more public gardens, less pesticide use and the replacement of lawns with a diverse range of native plants.

“Pollinators are perhaps the most intersectional biotic group of these times of global change: all human and non-human terrestrial communities rely upon them,” the authors write. “Improving our ability to track and understand their declines will be critical to our assessment of food security and ecosystem services in the future.”