Global Trends in Climate Suitability of Bees: Ups and Downs in a Warming World
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1. Introduction
The economic value of animal pollination as an ecosystem service in global agriculture ranges from USD 195 billion to USD 387 billion [1]. Additionally, it is estimated that pollinators play a direct role in supplying up to 40% of the essential nutrients in the human diet [2]. Insect pollination alone contributes to 9.5% of the total economic worth of agricultural products that are directly consumed by humans [3]. Notably, developed nations like Britain, Germany, and Japan are expected to face the most significant economic repercussions due to the decline of pollinators [4].
Research conducted by Rodger, Bennett [5] has demonstrated that a reduction in pollinators can result in a 50% decrease in seed-based reproduction for approximately one-third of flowering plants, indicating that a substantial number of flowering plants rely entirely on pollinators for seed production. Consequently, plants that depend on pollinators are susceptible to shifts in plant–pollinator interactions. In Brazil, where pollinator-dependent crops constituted 47% of all dietary nutrients in 2017, a decline in pollinator populations could lead to nutritional losses ranging from 8% to 30% [5].
Temperature changes have direct and indirect effects on insects. Direct effects encompass the influence on the activity levels of larvae and adults, their geographical distribution, phenology (timing of life cycle events), and growth duration. Indirect effects involve alterations in host plant phenology, variations in food quality, and shifts in predator and parasite dynamics [6]. Over the past century, there has been an average global temperature increase of approximately 0.6 degrees [7]. Projections indicate that global warming could range from 1.5 to 5.8 degrees by the close of the 21st century [8].
It is well established that climate change and land use alterations have substantial implications for plant–pollinator relationships [9]. One of the most significant effects is the emergence of temporal and spatial mismatches [10,11]. Numerous studies have investigated the impact of climate change on insect pollinators, with a particular focus on bees. Many of these studies have examined limited insect species and geographic regions. In general, rising temperatures are likely to compel bee species to migrate towards higher latitudes and polar areas [12,13]. For instance, Rasmont, Franzén [14] predicted a decline in bumblebee diversity in Europe by 2050 due to climate change, suggesting that only specific regions, including mountainous areas, might maintain a significant portion of their existing diversity by 2100. Similarly, Suzuki-Ohno, Yokoyama [15] observed a reduction in the distribution range of five bumblebee species in Japan over 26 years attributed to climate change.
To anticipate the community-level consequences of climate change, it is essential to initially comprehend the individual responses of each species to these climatic shifts [16]. Recent studies have underscored that the impacts of climate change on certain pollinating insects have become increasingly evident in recent years. Projections for the future suggest that the distribution of these species will undergo alterations due to ongoing climate change. In addition, temperature fluctuations significantly influence the metabolic rates of insects. These variations play a pivotal role, often resulting in observable shifts in how these creatures regulate their energy and biological processes [17].
Pollinating insects encompass various groups such as moths, butterflies, bumblebees, honeybees, solitary bees, and hoverflies. Among these, bees hold particular importance as they are accountable for pollinating approximately 35% of the world’s food production [18]. Bees, categorized as ectothermic creatures, exhibit a significant reliance on the temperature of their habitat for their functioning. Honeybees and bumblebees are known to visit over 90% of global food crops [19]. However, to date, there has been a notable absence of research investigating the ramifications of climate change on the potential future ranges of bees on a global scale. Consequently, in this study, we aim to evaluate the potential impact of climate change on these species. To delve into the repercussions of climate change on the distribution of these essential pollinators, it is imperative to first establish a baseline understanding of their current geographic ranges. Subsequently, we will assess how each species might respond to anticipated shifts in climate conditions. Therefore, this study raises two pivotal questions: 1. What are the potential consequences of future climate changes on the global distribution of bees? 2. Which regions around the world are most susceptible to the effects of climate change on these species? By addressing these inquiries, we aim to shed light on the global-scale dynamics of pollinator distribution in a changing climate.
4. Discussion
We estimated the potential effects of climate change on 1365 bee species from seven families on a global scale. Our results for bee species exhibited varying responses to climate change in 2070. The extended time horizon utilized in our climate change scenario, spanning until 2070, poses inherent challenges due to the associated uncertainties and speculative nature of long-term projections. These uncertainties stem from various factors, including evolving climate models, potential socio-economic changes, and unforeseen technological advancements that may influence future climate trends. However, among bees, a majority, approximately 65%, are expected to see their range decline, with an average decrease ranging from 28% to 56%. Conversely, about 35% of bees are projected to encounter an increase in their distribution, averaging between 16% and 121%. Additionally, we found that Africa was the most vulnerable continent to climate change impacts on bee populations. Our critique raises an important point about the limitations of reporting bee range shifts on a global scale. Indeed, some bee species may experience extreme declines in certain parts of the world while increasing in others, and averaging these changes at the global scale may not accurately reflect the vulnerabilities of particular regions. Our research addressed this limitation by estimating the effects at the continental level, which can help to identify specific regions that are particularly vulnerable to climate change impacts on bees. This approach provided a more nuanced understanding of the potential effects of climate change on bees and can inform more targeted conservation efforts to protect these important pollinators.
Climate change scenarios typically involve rising temperatures. Most bees are ectothermic [41], meaning their body temperature is regulated by their environment. Warmer temperatures can potentially expand the suitable habitats for these species, allowing them to thrive in regions that were previously too cold. This expansion of temperature-appropriate zones can lead to an increase in distribution. Roughly 35% of the bee population examined in this study is anticipated to expand their geographic range, primarily favoring North America. However, this increase may not necessarily be advantageous for them because climate change can disrupt the timing of natural events, such as the flowering of plants and the emergence of bees [42,43,44]. Additionally, bees expanding their ranges may encounter new challenges, such as competition with native species or exposure to new predators and diseases [45,46]. Conversely, species facing distribution reductions may require targeted conservation strategies to mitigate the potential impacts on biodiversity and ecosystem services. Empirical findings based on fieldwork indicate that insects are already experiencing negative impacts from temperature changes, precipitation patterns, and other factors associated with climate change [47].
In the context of species distribution, it is typical to witness certain species expanding their ranges while others contract as a result of climate change. For example, Lima and Marchioro [48] anticipate that seven bee species will experience a decline in their suitable habitat, while three species will see an expansion in their suitable habitat in the future in Brazil. Dew, et al. [49] also found that as climate change continues, Ceratina australensis is expected to experience a broader expanse of suitable habitat. However, other research has reported a greater decline in the future distribution of bees attributed to climate change. For example, Giannini, et al. [50] investigated the effects of climate change on 216 bee species in the Eastern Amazon and found that 95% of the studied bees would experience a decline due to climate change. The observation that bumblebees have shifted to higher latitudes in recent years is also concerning, as it suggests that these insects are already experiencing significant impacts from climate change [12,15,51,52,53]. Indeed, it is important to acknowledge that the effects of climate change on bees may vary across species and regions. While some studies have shown that the distribution of certain bee species may decrease in response to climate change, other studies have found that some bee species may benefit from the changing climate and experience an increase in their distribution range [33,48,49]. These findings highlight the complexity of the issue and the need for careful consideration of individual species and regional differences in assessing the potential impacts of climate change on bees.
Orr, Hughes, Chesters, Pickering, Zhu and Ascher [27] also employed the MaxEnt model to create a global species richness map for bees. Their findings revealed that bee hotspots are primarily concentrated in the southeastern United States, the Mediterranean basin, the Middle East, and Australia. Interestingly, tropical regions like Brazil do not display a high diversity of bee species. This distribution pattern aligns with the bimodal latitudinal pattern of bee richness described by [54], where warmer and drier areas appear to be more conducive to bee species diversity. Notably, xeric and non-forested regions play a pivotal role in driving bee biodiversity worldwide [27].
5. Conclusions
This study revealed the anticipated significant impact of climate change on global bee populations, indicating that a majority of species, roughly 65%, are likely to witness a decline in their distribution and suitable habitats, notably in Africa and Europe. Among continents, North America stands out with a considerable increase in bees expanding their distribution, contrasting with nearly 50% of bees projected to decrease in the future. While acknowledging the established role of non-bee pollinators, such as butterflies, moths, and hoverflies [55,56], in pollination, our research narrowed its focus to bees due to their recognized significance. Similar declines in distribution due to climate change are also being observed among other insect pollinators like butterflies, moths, and hoverflies [57,58,59,60,61]. It is important to note that in this study, our primary focus was on estimating the effects of climate change on bees. While our findings shed light on the impact of climate change, it is crucial to emphasize that habitat alteration, rather than climate change, is the primary driver of pollinator decline [62]. Habitat loss is commonly regarded as the primary driver behind the decline of bee populations [62,63,64].
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