Climate Change to Threaten Bee Populations in the Cape Floristic Region of Southern Africa

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, M., Guo, Danni., VEldtman, R., Donaldson, J., 2012 Consequences of warming up a hotspot: species range shifts within a centre of bee diversity. Diversity and Distributions, 2012.

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.

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