Warmer Climates Lead to Loss of Pollinator Diversity, Research Finds

A bumble bee visiting salvia flowers
A super-generalist bumble bee (Bombus terrestris) visiting salvia flowers (Salvia farinacea) in an urban area. Cristina Ganuza

The importance of bees as pollinators of the world’s food crops is well-known, but wasps, flies, beetles and other insects are also vital pollen conveyors. Pollination by insects is necessary for the growth of about 75 percent of the world’s food and more than 80 percent of wild plants. Crop pollination across the globe is estimated to be worth as much as $577 billion per year.

Insect declines due to habitat lost to agriculture and urbanization have been well-studied, but another factor that has affected pollinator communities is global warming. A new study from the Julius-Maximilian University of Würzburg (JMU) looks at how, as climates become warmer and drier, the combination of shifting land uses with the warming climate can have a detrimental effect on insect diversity, and what can be done about it.

The researchers examined more than 3,200 identified species of pollinators from 179 locations across Bavaria. They found that warmer climates — whether they were in grassland, forests, arable or urban habitats — led to an overall loss of pollinator diversity, indicating that increased warming as a result of the climate crisis would lead to greater loss of diversity in pollinator communities.

Cristina Ganuza, a Ph.D. student at JMU’s Department of Animal Ecology and Tropical Biology at the Biocenter, who was the lead author of the study, said that “the combination of ongoing climate change and current land use will only allow certain pollinator species to survive in different habitat types,” a recent press release from JMU stated.

The study, “Interactive effects of climate and land use on pollinator diversity differ among taxa and scales,” was published in the journal Science Advances.

“The study underpins that in addition to the importance of floral resources and the negative effects of land use intensification, climatic conditions play an increasingly important role for the maintenance of pollinator diversity. For example, the combination of high temperatures and low precipitation negatively affected total pollinator diversity, while bee richness in urban areas was negatively affected by higher mean temperatures,” said professor Ingolf Steffan-Dewenter, co-author of the study and head of the Department of Animal Ecology and Tropical Biology at JMU, in the press release.

Homogenized communities of pollinators can lead to lower crop yields, as not all species pollinate all types of plants.

“Several studies have shown that higher pollinator diversity correlates with higher yields of many crops. Crop yield increases with the number of pollinators, but also with their diversity,” Ganuza told EcoWatch. “Different pollinators visit different flowering plants. Some insects are generalists and can feed on multiple flowering-plant species, while others are specialists of a few plant species. Therefore, the higher the number of flowering-plant species, the higher the number of pollinator species. At the same time, a high pollinator diversity is needed to maintain a high flowering-plant diversity. They are mutualists and need each other.”

Warmer temperatures can be beneficial for insects, including pollinators, but only up to a certain point.

“First, pollinators and other insects are adapted to the region where they live and are able to resist changes in temperature to a certain limit. Warm temperatures within the range of tolerance of the different species are positive, because ectothermic insects can be more active than with cooler temperatures. However, if high temperatures rise too high, this limits the activity of insects and can even disrupt physiological processes,” Ganuza said. “Second, it is not only the increase in temperature that matters, precipitation patterns matter too. We are experiencing droughts more often, and many insects need water or moisture during their life cycle. Third, pollinators depend on flowering plants because they feed on nectar and pollen. If some plant species disappear because the climate got too warm or too dry, the pollinators that depend on them will disappear too. All in all, climate change is forcing insects to move to cooler regions, to change their phenology (to advance or delay their life cycle) or to change their physiology, which is an evolutionary process that normally happens much slower than climate change.”

The study showed that individual pollinator species responded differently to climates that were warmer and drier, but overall, forested landscapes maintained pollinator communities that were more diverse.

“One key finding therefore is that forest in the landscape can cushion the effects of climate warming to a certain extent,” said Ganuza, according to the press release.

“Based on other studies, we know that forests experience less temperature fluctuations than open habitats, because of their shady and moist conditions,” Ganuza told EcoWatch.

Planting more greenery in cities would make urban landscapes cooler and more amenable to insects and other animals.

“The temperature in cities could be lowered by decreasing the impervious surface and increasing the green areas. This can be achieved with green roofs and walls, planting trees, preserving parks and other non-built areas. Also promoting the use of public transport or bicycles would help, since heavy traffic contributes to increasing the heat-island effect of cities,” Ganuza told EcoWatch.

Diverse landscapes that include a variety of flowering plants ⁠— which lead to a greater array of insects, including pollinators, and other wildlife ⁠— are becoming increasingly important in the battle against biodiversity decline on a warming planet.

“At least in our study region in Germany, the presence of forest in the landscape can buffer the effects of climate warming to some extent, while large urban areas can worsen them. In general, pollinators need natural areas with abundant and diverse flower resources, but natural areas are increasingly threatened globally by intensive agriculture, monoculture forestry, deforestation and urban expansion,” Ganuza said.

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