Clik here to view.
Image copyright Carin Bondar 'The Nature of Human Nature'
I’m not a huge fan of the ‘all you can eat buffet’. I find it akin to a bunch of humans pulled up to the feeding trough plowing through as much as they can as though their lives depend on it. It’s the crowding that I don’t like, the lineup of people at the prime-rib station, drooling as their cut of meat is hefted onto their overstuffed plates. I think that my behavior at the buffet is directly correlated to the number of people are lingering around a specific area. If I had the place all to myself, I would be more inclined to hit the hot ticket items; however, when it is busy and the best parts have been completely picked over it is probably best to explore the other available options. Optimal foraging theory (OPT) predicts that when there is intense competition for preferred resources, organisms should increase their diet breadth to include other (less optimal) items1. In this way biological fitness is maximized by striking a balance between obtaining food and the amount of time and energy required to do so. Prime rib becomes less valuable if there is a 20 minute wait attached to it. I am in complete agreement with OPT on this one. Instead of waiting for a meat slab or fighting over crab legs, I’d rather eat something that may be less ‘valuable’ but is all mine.
Image may be NSFW.
Clik here to view.
A field full of flowering plants can be thought of as an ‘all you can eat buffet’ for pollinating organisms. Invertebrates from butterflies to bees can indulge on a plethora of plant items that are only too happy to share their wares (ingestion by pollinators = pollination = reproductive success of the plant involved). Many plants have evolved specialized coloration, morphologies and scents in order to make themselves more attractive to potential pollinators, not entirely unlike the garnishes, scents and presentations of the various foodstuffs available at our buffets. But what happens when the natural buffet becomes crowded? Do pollinators wait in line for their chance at the hot ticket flowers or do they follow the tenets laid out by OPT and forage on something a little less exciting? In an attempt to answer this question, laboratory experiments were conducted to assess the food choices made by the common bumblebee (Bombus terrestris) in crowded and non-crowded environments2. Artificial plant communities were created and comprised of a variety of species that included both high rewarding (i.e. prime rib) and poorly rewarding (i.e. peas and corn) types. Individually marked bees were followed in two situations: with only one other conspecific present (low density), or with 6 conspecifics present (high density). The number of visits made by the marked bees to each type of plant was recorded in each situation. True to the predictions of OPT, the diet breadth of individual bumblebees was increased when the buffet was crowded. Low-rewarding plant species that were visited only 6% of the time in the low-density treatment were visited 32% of the time in the high density situation, indicating that not all of the bees were willing to compete for the prime rib. Interestingly, the diet of the bees was most specialized when the buffet was not crowded (i.e. exclusively high quality foods were selected). Although this may be an optimal situation for the individual bee involved, it doesn’t help to maintain the diversity of the items available at the buffet. In this context an increased level of competition may actually work to preserve the biodiversity of the plant community by forcing other (non-popular) plant species to become pollinated as well.
Clik here to view.
The Pollinator Buffet
Many plant-pollinator interactions are opportunistic3, meaning that the interactions can vary through space and time and have the effect of maintaining the integrity of the system. It may be advantageous for a certain pollinating insect to feed on a particular food type at a specific time, but that insect maintains the ability to feed on other food sources if necessary. The key is to have the diversity to be able to withstand temporary alterations in conditions. When something like mad cow disease rears its ugly head and the popularity of the prime rib takes a nose dive, the buffet must be able to compensate by continuing to offer a variety of other things. Although like the individual bees, individual humans might be inclined to indulge in a single hot-ticket item if such an opportunity exists; this strategy isn’t optimal for the overall maintenance of the buffet, natural or otherwise. In addition, it isn’t optimal for maximizing biological fitness because organisms should be able to compensate for uncontrollable changes to their food supply. If the ability to do this is lost, the quest to obtain an adequate amount of nutrition becomes a lot harder. The overall message: a little crowding is beneficial to everyone. Despite the fact that there is only a tiny spoonful of peas and corn on your overloaded plate, you’d probably miss them if they were gone.
1MacArthur, R.H. and Pianka, E.R. 1966. On optimal use of patchy environment. The American Naturalist 100: 603–609.
2Fontaine, C., Collin, C.L. and Dajoz, I. 2008. Generalist foraging of pollinators: diet expansion at high density. Journal of Ecology 96: 1002-1010.
3Alarcon, R., Waser, N.M. and Ollerton, J. 2008. Year to year variation in the topology of a plant-pollinator interaction network. Oikos 117: 1796-1807.