By: Abby Satterwhite
Growing up in the Midwest, I came face-to-face with my first pollinator while laying underneath a trampoline located on a bed of dandelions and wild violets. My sisters and I liked to take turns performing solo dances and one-woman-shows on top of the trampoline while the spectators laid below on their backs, peering through the thin, black woven polypropylene. One spring afternoon, I laid below the trampoline watching my youngest sister’s interpretation of Rapunzel – if she had extremely long arms rather than extremely long hair – and I felt something on my skin I had never experienced before. A bee sting!
After my mom calmed me down and tended to my new wound, she explained to me why the bee was hanging out with us underneath the trampoline – she was hungry and got his food from flowers. It wasn’t until a couple years later that I understood the concept of pollination and plant reproduction. It became clear to me how all those flowers ended up in my backyard in the first place.
Among the yellow dandelions and purple wild violets, there were small patches of red flowers. The red flower was outnumbered and occurred sparsely.
-Why was the red flower less abundant than the yellow and purple flowers?
-Do bees prefer the taste or color of dandelions and violets?
These are questions that botanists and ecologists are still trying to understand. A recent study by Johnson et al. (2022) has made some important headway towards these questions by showing that competition for pollinators constitutes an advantage to favored plants and destabilizes the coexistence among species. Favored plants were more frequently visited by pollinators and proved to be more abundant and outcompeted their weaker adversaries.
Apis mellifera, the western honey bee, was the most abundant pollinator species in the Johnson et al. study (2022). Note the packet of pollen on the bee’s pollen basket (https://en.wikipedia.org/wiki/Pollen_basket) .
Some theories state that competition for pollinators may help strengthen plant coexistence. When generalist pollinators in the community limit different species, competition may strengthen niche differences and strengthen coexistence among plants. Everybody loves good old fashioned healthy competition, right? However, Johnson and colleagues found that competition for pollinators destabilized plant coexistence because pollinators favored more common plants over rare ones (Johnson et al., 2022). In this case, there is no such thing as healthy competition.
To quantify the difference of the fitness and stabilizing niche among plant competitors, two treatments were given to the plots to limit the effects of competition not caused by pollinators. Focal plants were hand pollinated so they would only face competition for sunlight and soil. The other plant species were not hand pollinated and had to compete for sunlight, soil, and pollinators. These plants grow annually, so if they do not get pollinated, they will quickly die off and go locally extinct as a result of competitive exclusion.
Johnson and colleagues (2022) found that 30% of the studied flower species are able to coexist without the restriction of pollination (flowers were manually pollinated by conductors of the study). However when given pollination constraints and competition for pollinators, coexistence among plant species was significantly reduced. The authors also found that the flowers more frequently visited by pollinators possessed a more attractive floral arrangement.
In the case of my backyard and trampoline-gate, there was a lower abundance of red flowers simply possibly because the bees favored and were more attracted to the yellow and purple ones creating a competitive imbalance.
It is incredibly important to protect pollinators such as bees, butterflies, and other insects. A decline in pollinator populations will result in a decline of plant species as well. The competition for them would result in greater destabilization of ecosystems with insects favoring certain competitors putting less favored flowers at risk.
For plants who are already struggling to coexist with their more favored competitors, pollen limitation as a result of a pollinator decline is expected to harm performances and hinder plant diversity (Johnson et al., 2022).
The feeling of winning is great! Putting up a good fight is great! A reduction in plant diversity as a result of competition for declining pollinator species – not so great. Plants have coexisted for millions of years through mutualistic relationships with pollinators, but competition is thickening for weak competitors who struggle to attract natural pollinators.
Johnson, C.A., Dutt, P. & Levine, J.M. Competition for pollinators destabilizes plant coexistence. Nature 607, 721–725 (2022). https://doi.org/10.1038/s41586-022-04973-x
Trepte Andreas 2009, Western Honey Bee, digital photograph, Deutschland birds and fauna research, accessed 6 October 2022 https://en.wikipedia.org/wiki/Western_honey_bee#/media/File:Apis_mellifera_Western_honey_bee.jpg