The Fight for Bumblebees

*Guest post by Sonya Sharma, a student in Marc's 'Causes and Consequences of Diversity' class.

A rusty patched bumblebee (Getty Images)

Behind the scenes of the food we see stocked in grocery stores are arguably one of the most important organisms in the world, bumblebees (Bombus), which provide pollination in both natural and managed systems. However, human food security may be at risk because of the recent worldwide declines in bumblebee populations.

Land-use change is generally accepted as being the main driver of bumblebee abundance decline. Numerous studies have documented reductions in bumblebee populations more noticeably in areas that have gone through anthropogenic changes, such as agricultural intensification and urbanization. Bumblebee species richness seems to be positively correlated with the availability of grassland resources, such as pollen sources and nesting habitat, which are scarce in agricultural landscapes. Additionally, due to the mechanical disturbances across large areas that are characteristic of agricultural landscapes, they do not typically provide suitable habitat for wild bumblebee populations. Furthermore, bumblebees have a limited flight range, long colony cycle and specific food and nesting requirements that cause them to be especially susceptible to habitat loss.

Another factor that could be leading to the wild bumblebee decline is pathogen spillover from commercialized or domestic bumblebee populations. The commercialization of bumblebees as agricultural pollinators has inadvertently made wild populations more susceptible to a variety of emergent diseases and epidemics. Commercial rearing facilities provide an ideal environment for the development of a high load of pathogens and parasites because of the high density and high rates of transmission in these facilities. Constant pathogen spillover from commercialized bumble bees with high parasite loads could potentially extirpate small wild bumblebee populations. 
 

A bumblebee hive- similar to ones placed in agricultural landscapes (Wikipedia)

A further contributing factor to the decline in bumblebees is the use of pesticides. Specifically, neonicotinoid containing pesticides, which are most widely used globally, have been found to dramatically reduce egg-laying by queen bumblebees. To mitigate neonicotinoids detrimental effects, a new class of pesticides are being adopted worldwide, sulfoximines. However, a recent study suggests that sulfoximines may also diminish queen bumblebees’ reproductive capacity. Exposure to small amounts to a sulfoximine containing pesticide caused colonies to produce 54% fewer male drones and no new queen bees (Meeus et al., 2011). Therefore, pesticide use is very likely a contributing factor to the widespread bumblebee decline.

All factors considered; we can conclude that bumble bee populations are in serious risk of losing diversity and possibly going extinct. However, when it was proposed in June 2018 to include four species of bumblebee in the Californian Endangered Species Act, the state was sued by the Californian Farm Bureau Federation and six other agricultural associations. These groups argue that bees cannot be protected under this law because it defines candidate species as “bird, mammal, fish, amphibian, reptile or plant” and does not list any insects.

This conflict in government policy is not unique to California however, and is an example of the longstanding tension between conservation biologists and the agricultural industry about the protection of pollinators. If bumblebees were listed on the Californian Endangered Species Act it would restrict grazing, pesticides and the use of commercial bumblebees. It could also limit where bumblebee hives could be placed. Farmers and ranchers claim that listing bumble bees would harm agricultural production dramatically.

Other environmentalists suggest that attempts to conserve bumblebees should focus more on wildlife-friendly approaches such as increasing agricultural land set-asides, hedgerows and employing integrated pest management. Whatever the strategy taken through policy to protect bumblebees, it should aim to increase the abundance of grassland resources, reduce pathogen spillover from commercialized populations and reduce the use of harmful pesticides. How to create a policy that will appease both the agricultural industry and conservation biologists is still up for debate. However, all can agree that bumblebees are an indispensable member of both managed and natural ecosystems.

Works Cited:

Grixti, J. C., Wong, L. T., Cameron, S. A., & Favret, C. (2009). Decline of bumble bees (Bombus) in the North American Midwest. Biological Conservation, 142(1), 75–84.

Meeus, I., Brown, M. J. F., Graaf, D. C. D., & Smagghe, G. (2011). Effects of Invasive Parasites on Bumble Bee Declines. Conservation Biology, 25(4), 662–671.

Further reading:

Sulfoximine pesticide effects on bumble bees: https://www.the-scientist.com/news-opinion/New-Pesticide-Affects-Bumblebee-Reproduction-64647

California Cotton Growers petition: https://www.cottonfarming.com/special-report/seven-ag-groups-file-lawsuit-regarding-bumblebee-species/

Conservation Groups Join California in Legal Dispute Over Protecting Bumblebees: https://www.kqed.org/science/1956515/conservation-groups-join-california-in-legal-dispute-over-protecting-bumblebees

If Bumble Bees Become Endangered In California, Farmers Say It Sets A ‘Dangerous Precedent: http://www.capradio.org/articles/2020/02/05/if-bumble-bees-become-endangered-in-california-farmers-say-it-sets-a-dangerous-precedent/

Why Honey bees aren’t the buzz

*Guest post by Shannon Underwood, a student in Marc's 'Causes and Consequences of Diversity' class.

When you think “Save the Bees”, most likely a Honeybee comes to mind – this is primarily because they have become the flagship species for the current bee crisis. Although responsible for bringing the much-needed attention to the impact humans are having on our bee populations, they greatly misdirect the public, making a large number of people significantly less aware of the other 4,000 diverse bee species we have in North America¹⁴ – our wild (native) bees: the ones we should be more concerned about.

Fig 1. Adapted from Wilson, Forister, and Carril 2017. Above figure shows the total amount of bee species survey-participants thought were in the United States.

Pollinators are responsible for supporting 35% of the global agricultural landscapes¹⁵. Outside of agriculture, 80-95% of the native flowering plants that are found in natural ecosystems rely on animal pollinators for reproduction¹¹. Pollination is a fundamental ecosystem service provided by a variety of animals, however most efficiently by wild bees. The unique evolutionary histories that bees share with native plants has resulted in the vast diversity of traits seen among them (Photo 1), and communities with greater bee diversity have shown to be more productive than communities with poorer diversity¹² - largely because of greater resource partitioning by the wild bees. Their foraging preferences, differences in body shapes and sizes, as well as some species ability to perform a more effective technique of pollination called buzz pollination, make wild bees the most important group of pollinators.

 

 Photo 1: Shows the different body shapes and sizes of some wild bees. This rich diversity reflects their unique coevolution with plants.

Bees are facing substantial reductions in their diversity, range and abundances worldwide¹. In North America, there are currently 12 wild bee species that are recognized as ‘threatened’ under the IUCN Red-list. Staggeringly, all 12 of these species belong to the genus Bombus- commonly referred to as the Bumblebee. Over that last 20 years, Bumblebees have become one of the largest victims of decline in North America - with four species that faced a 23-87% shrinkage in their geographic range, and a precipitous 96% reduction in their abundance². A leading cause of the declines in wild bee populations has been largely attributed to land-use change¹. While the human population continues to expand, accumulating amounts of their natural habitat is lost and replaced with agricultural and urban landscapes. The fragmented habitats that remain often have decreased accessibility to green spaces and poorer nesting opportunities for bees. Making it harder for them to grab a foothold in the community – these human-added stressors put our wild bees at a much greater risk for extinction.

Fig 3. Adapted from Szabo et al. 2012. Shows the decline in the occurrence of B. affinis (A), B. terricola (B), B. pensylvanicus (C), and all bumblebee species (D) between the years of 1980-1990 (green) and 2000-2010 (blue).

The second most prominent impact on wild bee abundance and diversity has been greatly linked to invasive species like the common Western Honey bee¹. The Honeybee, native to the Old World region, has become an invasive species in all areas outside of its origin³. Their uniquely large colonies and hive formation make them the most valuable pollinator to humans in agriculture management. Wild bee health and productivity is often reduced in agricultural landscapes because of the high use of pesticides and lower foraging opportunities⁷. To compensate for this, the honeybee has become a highly used technique worldwide because they can be easily transported to a field for crop pollination- many policies and conservation efforts tend to primarily focus on the protection of such managed bee species because of this. But the positive attention that the honeybee receives publicly leaves many people unaware that it is even invasive in North America.

Honeybees are generalists – a common characteristic for many invasive species⁸. They can forage up to 2-3km outside of their hive and will recruit other colony-workers once a good food source is found, in order to maximize their foraging products³. Because of their large numbers, they can greatly increase the foraging competition for our already-threatened wild bee species. Honeybees are also prone to several diseases and can increase the risk of transmission to our wild bee populations³. Although the honeybee is valuable in agricultural pollination for its cost and time efficiency, in many cases wild pollinators are better at pollinating than the honeybee alone (Fig. 4). The honeybee lacks the ability to perform buzz pollination - the amount of pollen a queen Bumblebee can deposit to a blueberry flower in a single visit would require a honeybee to visit the same flower 4 times⁹. These small and diverse organisms are thus extremely important for sustaining healthy natural ecosystems, and so it becomes increasingly significant that we find ways to support their abundance and diversity during this new human-dominated era.

Fig. 4. Adapted from Garibaldi et al. 2013. The figure shows that wild insects increased reproduction (y-axis) in all crops examined than the honeybee alone.

Cities are commonly viewed as human-dominated landscapes that are inhabitable for wildlife. However, some people argue that cities may actually be ecologically valuable to certain types of species like our insect-pollinators⁷. Cities often have less pesticide than the surrounding rural landscapes⁷, and the commonly used green infrastructures like green roofs, gardens, and parks can be extremely valuable to pollinators by offering more abundant and diverse foraging opportunities. Green infrastructure in cities is also recognized as being important for decreasing flight times and even providing habitat for certain species⁴. Many beekeepers highlight that one of the best things anyone can do to support wild bees is to transform their property into a bee sanctuary. Plant pollinator-friendly gardens and even incorporate bee hotels into your backyard as a way to offer wild bees more opportunities in developed areas. You can also take part in projects like “Bees In My Backyard”  and “Bumble Bee watch”  to help conservationists collect information on our current bee populations. More importantly, though, just becoming educated about the threats to our wild bees and spreading awareness to the people around you is a crucial step towards refocusing our pollinator conservation efforts, and bringing the attention away from the honeybee and rightfully onto our wild bees.

Literature cited

1.     Brown, Mark J. F., and Robert J. Paxton. 2009. “The Conservation of Bees: A Global Perspective.” Apidologie 40(3): 410–16.

2.     Cameron, Sydney A. et al. 2011. “Patterns of Widespread Decline in North American Bumble Bees.” Proceedings of the National Academy of Sciences 108(2): 662–67.

3.     Colla, Sheila R., and J. Scott MacIvor. 2017. “Questioning Public Perception, Conservation Policy, and Recovery Actions for Honeybees in North America.” Conservation Biology 31(5): 1202–4.

4.     Dylewski, Łukasz, Łukasz Maćkowiak, and Weronika Banaszak‐Cibicka. 2019. “Are All Urban Green Spaces a Favourable Habitat for Pollinator Communities? Bees, Butterflies and Hoverflies in Different Urban Green Areas.” Ecological Entomology 44(5): 678–89.

5.     Garibaldi, Lucas A. et al. 2013. “Wild Pollinators Enhance Fruit Set of Crops Regardless of Honey Bee Abundance.” Science 339(6127): 1608–11.

6.     Graham, Kelsey K. “Beyond Honey Bees: Wild Bees Are Also Key Pollinators, and Some Species Are Disappearing.” The Conversation. http://theconversation.com/beyond-honey-bees-wild-bees-are-also-key-pollinators-and-some-species-are-disappearing-89214 (February 20, 2020).

7.     Hall, Damon M. et al. 2017. “The city as a refuge for insect pollinators.” Conservation Biology 31(1): 24–29.

8.     “Invasive Species | U.S. Climate Resilience Toolkit.” https://toolkit.climate.gov/topics/ecosystem-vulnerability/invasive-species (February 21, 2020).

9.     Javorek, S. K., K. E. Mackenzie, and S. P. Vander Kloet. 2002. “Comparative Pollination Effectiveness Among Bees (Hymenoptera: Apoidea) on Lowbush Blueberry (Ericaceae: Vaccinium Angustifolium).” Annals of the Entomological Society of America 95(3): 345–51.

10.  Matias, Denise Margaret S. et al. 2017. “A Review of Ecosystem Service Benefits from Wild Bees across Social Contexts.” Ambio 46(4): 456–67.

11.  Ollerton J, Winfree R, Tarrant S: How many flowering plants are pollinated by animals? Oikos 2011, 120(3):321-326.

12.  Rogers, Shelley R., David R. Tarpy, and Hannah J. Burrack. 2014. “Bee Species Diversity Enhances Productivity and Stability in a Perennial Crop.” PLOS ONE 9(5): e97307.

13.  Szabo, Nora D. et al. 2012. “Do Pathogen Spillover, Pesticide Use, or Habitat Loss Explain Recent North American Bumblebee Declines?” Conservation Letters 5(3): 232–39.

14.  “The IUCN Red List of Threatened Species.” IUCN Red List of Threatened Species. https://www.iucnredlist.org/en (February 20, 2020).

15.  “What Are Pollinators and Why Do We Need Them? (Center for Pollinator Research).” Center for Pollinator Research (Penn State University). https://ento.psu.edu/pollinators/resources-and-outreach/what-are-pollinators-and-why-do-we-need-them (February 21, 2020).

16.  “Why bees matter.” Food and Agriculture Organization of the United Nations. 2018. http://www.fao.org/3/I9527EN/i9527en.PDF

17.  Wilson, Joseph S., Matthew L. Forister, and Olivia Messinger Carril. 2017. “Interest Exceeds Understanding in Public Support of Bee Conservation.” Frontiers in Ecology and the Environment 15(8): 460–66.

Un-BEE-lievable: The Buzz on Native Bee Conservation in Canada

Guest post by University of Toronto-Scarborough MEnvSc Candidate Rachel Siblock

Unless you’ve been living under a rock (much like native mining bees in Canada), you’ve probably seen the numerous campaigns to “Save the Bees”. Bee species across the globe are in decline. There are many factors that contribute to this decline, such as pesticide use, colony collapse, disease, habitat loss, and climate change¹. Many of these factors interact with one another, exacerbating the consequences and impacts. Conservation efforts are being implemented to try to stop the loss of these pollinators, and the valuable services they provide to humans. Canada is no exception. There are local, provincial, and national policies and programs operating and currently being developed in order to reduce the impacts of these threats. In the past few years, programs like The Bee Cause, Bees Matter, Feed the Bees, and others have implemented programs and recommendations in order to increase the bee populations in Canada. Honey Nut Cheerios has even campaigned to get the public engaged and involved in the conservation of bees. These programs, however, all have one common issue: they focus their efforts on Honey Bees. 

An example of a campaign by Honey Nut Cheerios, focusing on honey bees. 

There are no native honey bees in Canada. The most well-known bee in Canada was not even present in the country until it was introduced from Europe in the 1600s². The European Honey Bee was intentionally introduced to Canada for honey production, and since has increased in number dramatically, both in farmed and wild colonies. Honey bees have large colonies, allowing them to be easily managed and farmed. They also pollinate crops and produce honey, which may make them seem more economically valuable than their native, non-honey-producing counterparts. However, there have been unexpected impacts of the introduction of the European Honey Bee on native bee species in Canada.

            There are over 800 native bee species in Canada. While there are many different types of bees in Canada, the best understood group of native bees are bumble bees. Bumble bees have the ability to buzz pollinate, which allows them to obtain pollen from plants with pollen that is difficult to extract. Many of these plants are economically valuable, such as kiwi and blueberry crops. This, along with general pollination, makes managed populations of bumble bees worth several billion dollars annually³. Bumble bees naturally have low genetic diversity and can be subject to inbreeding depression, leading to declining populations and making the some species more vulnerable to extinction⁴. Threats can then interact with these low population levels, and intensify population loss. 

A male Rusty-patched Bumble Bee, one of Canada’s native bee species. It is currently listed as endangered in Canada.

Aside from facing the same threats as honey bees, native bumble bees are also threatened by the very presence of honey bees. Competition for resources with honey bees is a major threat to native bumble bees. A study performed in the United Kingdom found that bumble bees at sites with high honey bee density were significantly smaller in body size when compared to their relatives at sites with low honey bee density⁵. An additional study discovered a reduction of native bumble bee colony success when colonies were experimentally exposed to honey bees⁶. Honey bees generally produce larger colony sizes which can store a larger amount of resources than bumble bees. They also have the ability to communicate with one another about valuable floral resource locations⁷. Honey bees have a larger foraging range than native bumble bees, and have an increased ability to forage on introduced plant species⁷. These adaptations allow honey bees to outcompete native bumble bees, and commandeer sparse resources in the area.

            Threats from honey bees do not just end at competition; pathogens and parasites specifically adapted to honey bees have been shown to have the ability to spread to wild bumble bee populations. Managed honey bees are known to carry higher than natural levels of pathogens⁸, which can be transmitted to wild bumble bee populations when the bees interact. In particular, two pathogens endemic to honey bees, C. bombi and N. bombi, are wreaking havoc on bumble bee populations. While these pathogens do not have lethal effects, their sublethal effects can be devastating to colonies. These pathogens cause reduced pollen loads, a decline in flowers visited per minute, slower growth rates of colonies, decreased queen reproductive rates, shortened life spans and diminished colony growth⁸. With small populations already, entire bumble bee colonies can be wiped out by these pathogens. Honey bee parasites, such as the Small Hive Beetle, have also been shown to be able to spread to bumble bee colonies, where they consume the wax, pollen, and nectar stores of hives⁸. While honey bees have co-evolved with these parasites and pathogens for eons, bumble bees have not had the time to adapt to these threats, making them much more vulnerable to these hazards. 

Small Hive Beetle infestation in a honey bee colony. 

But why do we care about losing native bees? The same concerns about the loss of honey bees applies to native bees. Native bee species pollinate crops and flowers, which we depend on for food. It is estimated that about one in three bites of food we consume can be traced back directly to pollination by bees and other pollinators. However, native bees have been found to be more effective pollinators than honey bees. Some plant species in Canada rely solely on native bees for their pollination. With the loss of native bees, these plants will also become endangered, along with many other food crops requiring pollination. Additionally, there is a severe lack of research into native bees. Research tends to focus on honey bee populations, resulting in much more knowledge of honey bee behaviours, adaptations, actions, and responses to stressors. The truth is, we don’t know much about native bee species in Canada. We have no idea what the consequences of the loss of these species will be. However, this does not excuse us from protecting these bees. If anything, this lack of knowledge should increase our urge to protect them, so we have the opportunity to learn about them in the future.

            The native bee species in Canada share little life history traits with the European Honey Bee⁸, making many conservation efforts that focus on honey bees unsuccessful. Focusing conservation efforts on one species may not address the specific needs of native bees. In addition, by focusing on improving honey bee populations, there will be increased stress on native bees, which will lead to a decline in their populations. If we continue with these conservation strategies, we may threaten native species further.

            An increase in honey bee populations will increase parasite and pathogen levels in native bees, and also increase the competition between honey bees and native bees. So what can you do to focus conservation efforts on native Canadian bees? For starters, avoid the use of pesticides, which will decrease already low populations⁸. Improve your knowledge of bee species, and report invasive or introduced species in areas used by native bee species. Plant a wide variety of native plants with high pollen and nectar concentrations to ensure newly emerging bees have the resources they need to survive. And finally, avoid tilling, mowing, or burning in areas where native bee species, particularly ground dwelling species, are known to live. With increased knowledge of native bee needs, and species specific conservation efforts, it is hoped that native bee species will begin to rebound. Let’s BEE positive!

BEE Informed – To get involved with native bee conservation check out these links:

Native Pollinator Initiative – Wildlife Preservation Canada

Bumble Bee Recovery – Wildlife Preservation Canada

Help Native Bees – Conservation Halton 

Native Bee Information – Canadian Wildlife Federation

BEE-bliography:

    1.     Pettis, J.S., and K.S. Delaplane. 2010. Coordinated responses to honey bee decline in the USA. Adipologie 41:256-263.

    2.     van Engelsdorp, D., and M.D. Meixner. 2010. A historical review of managed honey bee populations in Europe and the United Sates and the factors that may affect them. Journal of Invertebrate Pathology 103:80-95.    

    3.     James, R., and T.L. Pitts-Singer. 2008. Bee Pollination in Agricultural Ecosystems. Oxford University Press, USA.

    4.     Zayed, A., and L. Packer. 2005. Complementary sex determination substantially increases extinction proneness of haplodiploid populations. Proceedings of the National Academy of Sciences of the United States of America 102:10742-10746.

    5.     Goulson, D., and K. Sparrow. 2009. Evidence for competition between honey bees and bumble bees: Effects on bumble bee worker size. Journal of Insect Conservation 13:177-181.

    6.     Thomson, D. 2004. Competitive interactions between the invasive European honey bee and native bumble bees. Ecology 85:458-470.

    7.     Goulson, D. 2003. Effects of introduced bees on native ecosystems. Annual Review of Ecology, Evolution, and Systematics 34:1-26.

    8.     Colla, S.R. 2016. Status, threats and conservation recommendations for wild bumble bees (Bombus spp.) in Ontario, Canada: a review for policymakers and practitioners. Natural Areas Journal 36:412-426.

Image Sources:

  1. https://bringbackthebees.ca

  2. https://inaturalist.com

  3. http://beeaware.org.au/archive-pest/small-hive-beetle/#ad-image-0

Do green roofs enhance urban conservation?

Green roofs are now commonly included in the design of new public and private infrastructure, bolstered by energy savings, environmental recognition and certification, bylaw compliance, and in some cases tax or other direct monetary incentives (e.g., here).  While green roofs clearly provide local environmental benefits, such as reduced albedo (sunlight reflectance), storm water retention, CO₂ sequestration, etc., green roof proponents also frequently cite biodiversity and conservation enhancement as a benefit. This last claim has not been broadly tested, but existing data was assessed by Nicholas Williams and colleagues in a recent article published in the Journal of Applied Ecology.

Williams and colleagues compiled all available literature on biodiversity and conservation value of green roofs and they explicitly tested six hypotheses: 1) Green roofs support higher diversity and abundance compared to traditional roofs; 2) Green roofs support comparable diversity and composition to ground habitat; 3) Green roofs using native species support greater diversity than traditional green roofs; 4) Green roofs aid in rare species conservation; 5) Green roofs replicate natural communities; and 6) Green roofs facilitate organism movement through urban areas.

Photo by: Marc Cadotte

What is surprising is that given the abundance of papers on green roofs in ecology and environmental journals, very few quantitatively assessed some of these hypotheses. What is clear is that green roofs support greater diversity and abundance compared to non-green roofs, but we know very little about how green roofs compare to other remnant urban habitats in terms of species diversity, ecological processes, or rare species. Further, while some regions are starting to require that green roofs try to maximize native biodiversity, there are relatively few comparisons, but those that exist reveal substantial benefits for biodiverse green roofs.

How well green roofs replicate ground or natural communities is an important question, with insufficient evidence. It is important because, according to the authors, there is some movement to use green roofs to offset lost habitat elsewhere. This could represent an important policy shift, and one that may ultimately lead to lost habitats being replaced with lower quality ones. This is a policy direction that simply requires more science.

There is some evidence that green roofs, if designed correctly, could aid in rare species conservation. However, green roofs, which by definition are small patches in an inhospitable environment, may assist rare species management in only a few cases. The authors caution that enthusiasm for using green roofs to assist with rare species management needs to be tempered by designs that are biologically and ecologically meaningful to target species. They cite an example where green roofs in San Francisco were designed with a plant that is an important food source for an endangered butterfly, Bay Checkerspot, which currently persists in a few fragmented populations. The problem was that the maximum dispersal distance of the butterfly is about 5 km, and there are no populations within 15 km of the city. These green roofs have the potential to aid in rare species conservation, but it needs to be coupled with additional management activities, such as physically introducing the butterfly to the green roofs.

Overall, green do provide important environmental and ecological benefits in urban settings. Currently, very few studies document the ways in which green roofs provide ecological processes and services, enhance biodiversity, replicate other ground level habitats, or aid in biodiversity conservation. As the prevalence of green roofs increases, we will need scientifically valid ecological understanding of green roof benefits to better engage with municipal managers and affect policy.

Williams, N., Lundholm, J., & MacIvor, J. (2014). Do green roofs help urban biodiversity conservation? Journal of Applied Ecology DOI: 10.1111/1365-2664.12333

Unexpected effects of global warming in novel environments: butterflies emerge later in warming urban areas.

There is now ample evidence that warming temperatures cause advances in the timing of organismal activity (i.e., phenology). Studies have shown that rising temperatures are responsible for earlier plant leafing and flowering (Miller-Rushing & Primack 2008, Wolkovich et al. 2012), pest insect emergence and abundance (Willis et al. 2008), and even local species loss and reduced diversity (Willis et al. 2008). One emerging expectation from global warming studies is that insects should emerge earlier since winters are milder and spring temperatures are warmer. This expectation should hold so long as high temperatures or other environmental stressors don’t adversely affect the insects. And the concern about shifts in emergence and insect activity is the potential for mismatches between plant flowering and the availability of pollinators (Willmer 2012) –if insects emerge too soon, they may miss the flowers.

Photo by Marc Cadotte

In a forthcoming paper in Ecology by Sarah Diamond and colleagues study 20 common butterfly species across more than 80 sites in Ohio. These sites were located in a range of places across a rural to urban gradient. Instead of finding earlier emergence in warmer places, which were typically urban areas, they found that a number of species were delayed in warmer urban areas. Even though the butterflies might emerge earlier in warmer rural habitats, they were adversely affected in urbanized areas. 

These results highlight the need to consider multiple sources of stress from different types of environmental change. Observations from a few locales or from controlled experiments may not lead to conclusions about interactive influences or warming and urbanization, and that's why this study is so important. It observes a counter-intuitive result because of the influence of multiple stressors. 

A next step should be to determine if pollinator-plant interactions are being disrupted in these urban areas. The reason why we should care so much about pollinator emergence is that they provide a key ecological service by pollinator wild, garden, and agricultural plants, as well has being an important food source to other species. A mismatch in timing and disrupt these important interactions.

References

Diamond S.E., Cayton H., Wepprich T., Jenkins C.N., Dunn R.R., Haddad N.M. & Ries L. (2014). Unexpected phenological responses of butterflies to the interaction of urbanization and geographic temperature. Ecology.

Miller-Rushing A.J. & Primack R.B. (2008). Global warming and flowering times in Thoreau's Concord: a community perspective Ecology, 89, 332-341.

Roos J., Hopkins R., Kvarnheden A. & Dixelius C. (2011). The impact of global warming on plant diseases and insect vectors in Sweden. Eur J Plant Pathol, 129, 9-19.

Willis C.G., Ruhfel B., Primack R.B., Miller-Rushing A.J. & Davis C.C. (2008). Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change. Proceedings of the National Academy of Sciences, 105, 17029-17033.

Willmer P. (2012). Ecology: pollinator-plant synchrony tested by climate change. Curr. Biol., 22, R131-R132.

Wolkovich E.M., Cook B.I., Allen J.M., Crimmins T.M., Betancourt J.L., Travers S.E., Pau S., Regetz J., Davies T.J., Kraft N.J.B., Ault T.R., Bolmgren K., Mazer S.J., McCabe G.J., McGill B.J., Parmesan C., Salamin N., Schwartz M.D. & Cleland E.E. (2012). Warming experiments underpredict plant phenological responses to climate change. Nature, 485, 494-497.

Diamond, S., Cayton, H., Wepprich, T., Jenkins, C., Dunn, R., Haddad, N., & Ries, L. (2014). Unexpected phenological responses of butterflies to the interaction of urbanization and geographic temperature Ecology DOI: 10.1890/13-1848.1

The birds and the bees and the microbes

Vannette et al. 2013. “Nectar bacteria, but not yeast, weaken a plant-pollinator mutualism”. Proceedings of the Royal Society B-Biological Sciences.

"When we try to pick out anything by itself, we find it hitched to everything else in the Universe."- John Muir

You can’t help but marvel at the complexity of ecology, at the intricacy and multiplicity of species interactions. But this complexity is also problematic. For many ecologists, it becomes necessary to focus on a single type of interaction, or on interactions limited to only a few species. But real ecological systems are hardly ever limited to a single important process. They might include competition, mutualism, facilitation, predation, environmental constraints and fluctuations, additive and interactive effects, nonlinearities, thresholds and emergent properties. Can knowledge of  omplexity emerge from simplicity? Can simplicity emerge from complexity? These are important and longstanding questions in ecology, the focus of some of our smartest minds. We may not have the answer yet, but if nothing else, it is helpful when experimental work in community ecology attempts to explore multiple interactions.

For example, some of the work from Tadashi Fukami’s lab is focused on how communities of microorganisms (yeast and bacteria species) assemble in Mimulus aurantiacus nectar. In the past, this work has focused particularly on priority effects and resource competition, which plays an important role in structuring these communities. While past work has suggested the importance of pollinators as a dispersal vector for microorganisms, fascinating new work suggests that microbial communities have important effects on pollinators and their mutualistic interactions with the host plant as well.

Vannette et al. (2013) focused on the effects of the two most abundant species in Mimulus nectar, Gluconobacter sp., an acid-producing bacteria, and Metschnikowia reukaufii, a yeast. They then looked at three related questions – how do nectar microbes affect nectar chemistry, how do they affect nectar removal by hummingbird pollinators, and how to they affect pollination success and seed set. Basically, do nectar microbes disrupt important mutualistic interactions between the plant and their pollinators, or are their effects neutral?

This is where the story becomes interesting. Both types of microbes altered nectar chemistry, but in different ways. The bacteria acidified the nectar (to ~ pH 2.0) far more than the yeast species, and tended to also reduce the sugar content of the nectar far more than the yeast. Hypothesizing that these changes could ultimately affect pollinator preference, the authors then filled artificial flowers with nectar containing either the bacteria, yeast, or no microbes. Half of these flowers were bagged to prevent hummingbird access. Compared to the bagged controls, flowers with bacteria-inoculated nectar had less nectar removed than either yeast-inoculated or sterile nectar. It appeared that nectar removal was related to the changes in chemistry driven by bacterial growth in the nectar. Finally,  the authors looked pollination success in relation to microbial inoculation. Flowers inoculated with bacteria did indeed have less pollination success (measured as the number of stigmas closed) and had decreased seed numbers. Microbial communities were not isolated from the ecology of the plant.

Perhaps none of this is that surprising – hummingbirds are intelligent and will preferentially feed, and pollinator choice is important for plant fitness. However, these bacteria and yeast species are specialized for growth in the hypertonic nectar environment and their continued presence in the ecosystem depends on dispersal from one flower to the next before their host flower dies. The transient nature of this nectar habitat suggests that obtaining a dispersal vector should be important. The fact that Gluconobacter alters nectar chemistry in a way which negatively affects their likelihood of movement to other patches suggests an interesting paradox and a complicated relationship between plants, their nectar microbes, and pollinators. Gluconobacter species growing in Mimulus flowers produce acidifying H+ ions and reduce sugar concentrations in nectar – this increases their likelihood of winning competitive interactions with other microbes in the nectar, which should select for the maintenance of acidifying, sugar-reducing characteristics. But on the other hand, these characteristics reduce the likelihood of being transported to new flowers and persisting in the metacommunity. Further, these pollinator-decreasing characteristics may result in selection by the Mimulus plants for nectar compounds that reduce microbial contamination. So understanding competitive interactions in microbial communities, or understanding pollinator-plant interactions, or understanding pollinator-microbial interactions on their own might be inadequate to understand the important ecological and evolutionary processes structuring the entire system.

Given that the question of simplicity vs. complexity is still so difficult and at least for me, uncertain, I would hesitate to draw a general conclusion about whether this is the kind of work all community ecologists should strive for. But it seems that recognizing ecological and evolutionary context is key, whether you work with Arabidopsis, microcosms, or tropical forests.