Category Archives: Climate Change

What is Climate Change doing to our Bees?

Insect pollinators ensure transfer of genetic material between plants (sexual reproduction) and maximisation of fruit sets and yields. However these beneficial insects are in decline worldwide, owing to the intensification in crop production of the 20th century (giving less diverse forage), misuse of pesticides and proliferation of various diseases. A driver of decline still under contention is global warming (more accurately climate change) as the effects are hard to predict and will be different for specific groups of pollination- an optimum foraging temperature for bees may be not be so good for pollinating moths, butterflies, hoverflies or birds.

Temperature too high?

Many insects are ectotherms, meaning they do no generate their own heat and need to bask in the sun to become warm enough. Pollinator groups such as butterflies have their distributions limited by low temperatures at high latitudes, so when the climate warms in these areas the generalist species (those that may feed on a wide breadth of flowers) are expected to expand their distribution northwards, but a colder winter temperature will cause their range to recede southwards. For bumblebees the relationship is not as clear- some species have retreated northwards (Bombus distinguendus) and others have retreated southwards (B. sylvarum). Other problems may arise for bumblebee queens that overwinter and emerge from dormancy to find their newly-found colonies is out of sync with their forage plants- this is known as a phenological mismatch or phenotypic asynchrony.

Out-of-sync with host plants?

Climate change is causing phenological advances (a delay) of flowering in plants which means insects have a shorter foraging season to feed and raise their young (either by feeding larvae or provisioning resources to eggs). Non-Apis bees (bees other than honeybees) in particular are shifting in relation to their host plants, with their queens even emerging from overwintering to find very few nectar plants have flowered yet, suggesting no clear pattern for phenological mis-matching. But some researchers argue that in robust pollinator networks there is an assemblage of multiple plant species for early emerging or late emerging pollinators to feed on, and vice versa. For specialist pollinators there is also a risk of spatial mismatches, where plants offering nectar and pollen shift their range and distribution much to the chagrin of specialist pollinators that must ‘track’ their host plant by migration (but this depends on dispersal ability, commonness of preferred nesting habitat). Generalists, however, will be able to take advantage of biodiversity of forage plants and will be affected less. In response to pressures to alter their diet, some bee species have even been rapidly evolving shorter tongues in order to feed from plants with shallower corollas. In 40 years, 2 alpine species of bumblebee (Bombus balteatus and B. sylvicola) have reduced their tongue length by 3 millimetres in response to a 60% decline in flower production.

Pollinating-moth-feeds-from-Sacred-Dutura

Exacerbating other drivers of decline?

Climate change may interact synergistically with other causes of declines, for instance increased temperatures may speed up pathogen growth rates and lead to increased proliferation of bee parasites, such as varroa mite. Climate warming is speculated to increase the competition for resources between native bees and invasive ‘super-generalists’, possibly leading to extinction by competitive exclusion. Climate change may also cause development of agricultural methods that have an adverse effect on bees, such as devoting more land to growing crop monocultures (reducing florally diverse habitats) or increased use of pesticides.

What can be done?

Efforts are being made to help sustain pollinator diversity in agricultural landscapes, such as the compulsory planting of wildflowers through environmental stewardship schemes. However some researchers argue the existing biodiversity of food plants will ensure plant-pollinator phenological synchrony against climate change, and only very specialist feeders will be at risk. The rapid evolution of some at-risk bee species (such as those with shorter tongues) will also play a key role in recovery of pollinator populations. Efforts to mitigate the effects of climate change (such as reduction of emissions and geo-engineering solutions) would also reduce the subsequent effects on pollinator decline.

Further Reading:

Bartomeus, I., Ascher, J. S., Wagner, D., Danforth, B. N., Colla, S., Kornbluth, S., & Winfree, R. (2011). Climate-associated phenological advances in bee pollinators and bee-pollinated plants. Proceedings of the National Academy of Sciences108(51), 20645-20649.

Burkle, L. A., Marlin, J. C., & Knight, T. M. (2013). Plant-pollinator interactions over 120 years: loss of species, co-occurrence, and function. Science,339(6127), 1611-1615.

Garibaldi, L. A., Steffan-Dewenter, I., Winfree, R., Aizen, M. A., Bommarco, R., Cunningham, S. A., … & Klein, A. M. (2013). Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science, 339(6127), 1608-1611.

Miller-Struttmann, N. E., Geib, J. C., Franklin, J. D., Kevan, P. G., Holdo, R. M., Ebert-May, D., … & Galen, C. (2015). Functional mismatch in a bumble bee pollination mutualism under climate change. Science349(6255), 1541-1544.

Advertisements

Decline of Pollinators could Worsen Global Malnutrition

Bee4file95912727831604417beetle_lg2

Pollinators contribute to about 10% of the economic value of crop production, but the contribution to human nutrition by these pollinators is potentially much higher. This is because pollinators support the sexual reproduction (by transfer of gametes aka pollen) of crops high in essential nutrients that malnourished regions of the world rely on. This suggests that regions already facing food shortages and nutritional deficiencies will suffer particularly hard from the global decline of bees and other pollinators.

Many of the crops dependent on animal vectors to pollinate (instead of wind) are the ones most rich in micronutrients essential for human health. The recent decline of important pollinators, such as the domesticated Western honey bee, Apis mellifera, has lead to concerns on the economic and now nutritional situation of crop production.  Dr Chaplin-Kramer and colleagues set out to assess the importance of pollinators to global health by determining which regions these crops are most critical for and what their micro-nutrient content is.

The research concluded that pollinator decline could affect different regions of the world in entirely different ways. Developed regions such as China, Japan, U.S.A. and Europe relied on natural pollinators for producing crops of high economic value, whereas lesser developed regions such as South Asia, India and sub-Saharan Africa relied on natural pollinators for producing crops of high nutritional value. Chaplin-Kramer and colleagues also mapped out hotspots that relied on 3 essential micro-nutrients; iron, vitamin A and folate. The regions depending most on pollination for nutrition delivery also tend to have high rates of malnutrition and poverty.

The health concerns potentially resulting from this include vitamin A deficiency, which is associated with blindness and increased risk of disease, iron deficiency which causes anaemia and pregnancy complications, and lack of folate that causes folate deficiency anemia. This study has also highlighted that the effects of pollinator decline are much more diverse and widespread than the well-known crop production and income problems. However there are ways for the regions to adapt to changes to pollination services, such as using managed bee colonies to supplement wild populations, switching to alternative nutrition-equivalent crops less reliant on bee pollination and importing nutrient-rich foods from other countries.

Chaplin-Kramer, R., Dombeck, E., Gerber, J., Knuth, K. A., Mueller, N. D., Mueller, M., … & Klein, A. M. (2014). Global malnutrition overlaps with pollinator-dependent micronutrient production. Proceedings of the Royal Society B: Biological Sciences, 281(1794), 20141799.