Bees are a critical pollinator in global food systems and thus a keystone species in the maintenance of healthy ecosystems. The Cape Floristic Region of South Africa enjoys a high level of ecological diversity however in the last five years multiple studies have demonstrated statistically significant increases in mean daily temperatures in both its winter and summer rainfall areas. The threats climate change pose to both generalized and specialized bee species have begun to be documented in Europe however, despite their importance, no similar research has been done into South African bee populations. Changes in temperature and meteorological conditions could have a negative impact on bee species’ ranges and population numbers in the coming century. Kuhlmann et al. (2012) thus seek to determine what effect, if any, climate change will have on twelve major ground dwelling bee species in the Cape Floristic Region (CFR) of South Africa. The researchers compared current and historical bee population data for the twelve species with future climate projections in the region based off the WorldClim Data Base and the 2006 Land Cover Project. Kuhlmann et al. (2012) found climate change to threaten bee ranges across the board with greater risks to winter rainfall species.
Kuhlmann et al. (2012) chose for their study twelve ground-dwelling bee species from the CFR due to the comparatively significant distribution records available for them, their occurrence in both the winter and summer rainfall areas, as well as their overall importance as pollinators. Historical bee records from museums and natural records were collected irrespective of date, however a vast majority of available data dates from after 1980. Kuhlmann et al. used the program MaxEnt to model potential future geographic ranges for the twelve bee species. This program was selected because it can make up for relative small sample sizes by comparing input data with larger systematic ecological surveys. The MaxEnt projections were compared to the results of the HadCM3, or the Hadley Centre Climate Model, a climate projection model which is favored by scientists studying the CFR. Kuhlmann et al. modeled two scenarios for climate change by 2080, one in which the CFR had a high increase in population and CO2 emissions, and a second in which a commitment to environmental preservation prevents population and emission increase. The researchers chose a number of climatic and environmental variables in their projections with a focus on seasonality in rainfall, which is a critical factor in bee ranges.
Regardless of the climate scenario used, the results of Kuhlmann et al. suggests thatclimate change will have a major impact on the geographic ranges of all twelve bee species studied. If seasonal rainfall rates are impacted as these results suggest, eight of the twelve species of bees will see a net reduction of possible geographic range with five species seeing dangerously dramatic decreases. While changes to the species of the summer rainfall region are marked by shifts in geographic ranges, species of the winter rainfall species face reduction in overall geographic ranges, thus making them markedly more vulnerable to climate change in the region. Previous studies have suggested that the summer rainfall species have the capacity to travel east in the CFR to more favorable climate ranges in the future. However, for some species such as Patellapis, which are primitively social at higher temperatures and serves as major pollinators in the region, may become more abundant as winters warm over the coming decade.
Given that this is the first study of its kind in the CFR, Kuhlmann et al. are careful to ground their results with a call for further research. Of particular importance for researchers of pollinators and climate change is the issue of plant-pollinator interaction. The bee species studied in this article show little to no synchronization with their host plants, leading to the hypothesis that even if bees are able to migrate in the CFR, if their host plants are negatively impacted by climate change it could be enough to decimate these bee populations. Kuhlmann et al. argue for establishing population monitoring facilities in the coastal lowlands of the CFR for further study of the winter rainfall species which are believed to be especially at risk from climate warming.
Healthy bumble bee (Bombus) populations are essential to the pollination of commercial agriculture and wild plant communities in the United States. Unfortunately, initial studies confirmed the widespread fear that American bee numbers were drastically shrinking. Cameron et al. (2011) make important progress in understanding the reasons behind the dwindling number of bumble bees through a three year interdisciplinary research project tracking distribution patterns, genetic diversity and pathogen infection levels in bumble bee populations in each major bee region of the United States. Their research confirms that the presence of four major species has declined by up to 96% while their geographic presence has shrunk 23–87% over the last two decades. Furthermore, declining populations are distinguished by the presence of the pathogen Nosemba bombi and low levels of geographic diversity. While the research provides pathogen levels and genetic diversity as predictors for population collapse, the cause remains unknown.–Michael Landsman
American food production has become dependent upon bumble bees for pollination since recent domestication in major agricultural areas. Their comparatively large anatomy, long tongues and high frequency buzzing, which helps scatter pollen off their bodies, make them uniquely efficient pollinators. Recently North America has joined other global regions in witnessing disturbingly fast-paced bee population decline. Various hypotheses speculating on the causes of bee decline have been made yet Cameron et al. (2011) represents the first major study into the problem in North America. This study sought to accomplish two major tasks; to quantitatively demonstrate a reduction in bumble bee populations and geographic ranges, as well as to test for two of the projected reasons for population decline, pathogens and genetic diversity levels. To quantify current population and geographical ranges, the team chose four varieties of the bumble bee in North America and compared empirical data from the last two decades with a count taken between 2007 and 2009 at over three hundred locations in North America. To determine pathogen infection rates and genetic diversity, the project examined midgut tissue samples of over six thousand bumble bees from representative regions and performed genotypes on both stable and declining populations. Their findings demonstrate both an overall reduction in bumble bee population numbers and geographic ranges and that communities which have suffered the most feature low levels of genetic diversity and a prevalence of the pathogen Nosemba Bombi.
Many followers of bee decline in Europe have blamed the rising temperatures and diminished food sources resulting from climate change for the drastic drop in numbers. Cameron et al. (2011) have observed that in North America, even species which have previously withstood wide climactic variations are facing population collapse, thus they argue for the inclusion of other elements in exploring the root of the bee problem. While the widespread tissue study highlighted the prevalence of N. bombi in declining populations, the authors do not assert their study yielded sufficient evidence to argue the pathogen is a cause of decline; future research is required to determine whether or not N. bombi becomes a hallmark of populations already in decline. While bumble bees can pick up certain infectious pathogens from contact with flowers, no tests have yet explored whether N. bombi is transmitted this way. While the presence of N. bombi is a useful warning sign for threatened bee populations, there remains much more research to do in understanding the infectious agent’s exact role.
An exploration of genetic diversity in bumble bees through genotyping confirms initial suspicions that populations in decline suffered from smaller gene diversity. In a situation similar to that of the N. bombi question, further research needs to be done to determine whether small gene pools is a cause or effect of species dwindling. The genotype study found significant gene flow among populations across a very wide scale. While this is good news in the sense that there is a possibility for dwindling communities to diversify, it also means infectious contagions have the ability to travel long distances as well. The authors expect more research to be done in this area before definitive statements on the cause of this bee crisis. With regards to climate change, it would be useful to determine if limited gene diversity makes bumble bees more vulnerable to temperature variance. Hopefully a major study in PNAS and the dangerous threat to food production dwindling bumble bee numbers present will provoke further research in the area.