Article: Reduction in the Potential Distribution of Bumble Bees (Apidae: Bombus) in Mesoamerica Under Different Climate Change Scenarios: Conservation Implications by Martínez-López and colleagues (2021)
Background: Population surveys over the last decade have shown a global decrease in the abundance of bumble bees, with some species at great risk of extinction. Since bumble bees provide the invaluable service of pollinating a large proportion of wild plants and crops, this is one of the most concerning ecological issues of our time. There are a number of important factors contributing to the decline of bumble bees, including pesticide use and habitat loss, but the overarching and most challenging threat is climate change. Climate change threatens bee populations by causing shifts in suitable habitats and causing plant-pollinator mismatch. This plant-pollinator mismatch is a phenomenon where bee emergence and plant flowering, which have evolved to be synced, have started to occur at different times of the year due to climate change-- resulting in decreased plant reproduction and decreased bee survival. Research on how climate change will affect bee populations is limited for tropical regions. These regions are important because they are home to a large diversity of bee species, and they produce some of the world's most important crops, like coffee beans. Martinez-Lopez and colleagues used an ecological niche model to predict the future distribution of 18 bumble bee species across Mesoamerica under different climate change scenarios.
Methods: Ecological niche modeling is a process involving computer algorithms to predict species distribution over time by using environmental data. They utilized databases to gather nearly 35,000 occurrences of bumble bees across Mesoamerica (from Mexico to Panama) and used this information to establish the current distributions of 18 different species. Then, they gathered environmental and climatic data on the home ranges of these species to understand their ecological niches, or where they fit into the ecosystem based on their habitat requirements. Using multiple climate change predictions of varying greenhouse gas emissions, they predicted how these habitats will change under varying levels of climate change intensity. By knowing their habitat requirements and predicting how these habitats will change over time, Martinez-Lopez and colleagues were able to predict the distribution of each species in 2050.
Findings: Future bumble bee distributions across Mesoamerica varied greatly depending on the intensity of climate change used in the model, yet all species were predicted to experience a decrease in distribution. Some species’ distributions decreased by only 7% by 2050 under less intense climate change, while other species’ distributions decreased by 100% by 2050 under more intense climate change. Shrinking distributions could lead to some areas losing up to 8 species. Climate change is expected to force bees to move 100 to 500m higher in elevation. The species’ geographic centers are predicted to shift 1 to 581km by 2050. Further, among the 18 bee species, 14% of their distribution is in protected areas; however, this is expected to increase to 23% based on future climate change projections. In other words, the bees will be retreating to protected areas; the coverage of protected areas will not increase.
Conclusions: Even under the least intense climate change model, Martinez-Lopez and colleagues predict significant loss in bumble bee distribution that will likely have both ecological and economic consequences. When considering compounding threats like pesticide use and habitat loss, the consequences are likely to be even greater. Furthermore, these predictions assume populations will be able to make large shifts in geographic range to survive. Fragmented habitats or other barriers to movement could prevent populations from establishing in new areas. Although land conservation is highly important to protect biodiversity, researchers suggest it will not be enough to prevent serious losses to bumble bee populations in Mesoamerica. Conservation efforts need to include restoring forests with native plants, promoting native flowering plants in urban gardens, and land management where conservationists and farmers actively work to restore the landscape.
Figure: Change in the number of species due to climate change in 2050. More red colors represent a loss of species and more green colors represent the addition of species to that area.
Reference:
Martínez‐López, O., et al. "Reduction in the potential distribution of bumble bees (Apidae: Bombus) in Mesoamerica under different climate change scenarios: conservation implications." Global Change Biology (2021).
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