Ecological compensation mechanisms within pollinator communities in the face of species loss

Posted May 13th, 2010 at 3:02 pm.

Sarah Allard and Kristin Jenkins

Mentor: Dr. Neal Williams

Ecosystem services are processes and contributions from the natural world that are essential to human well-being. Among the most important of these services is pollination, which is provided primarily by bees and is required for the successful production of half of the world’s crops. Recent declines in managed honeybees and concerns about food security in an increasingly populous world make it imperative that we understand the role of other wild bee species and the factors that influence pollination to ensure stable pollination. A series of recent articles suggest that pollination, like other ecosystem services, is dependent upon diversity and abundance of species within a system, thus loss of biodiversity may severely impact crop pollination and production. This may occur because the total level of pollination service provided depends on the number of individual bees visiting a crop and on the amount of pollination each individual provides.

# of pollinators x pollination per pollinator – total pollination

Pollinator loss due to human influence could be compensated for by an increase in the number of individuals of remaining species, called numerical compensation. Alternatively species loss could be made up for not an increase in populations, but by an increase in the level of pollination performed by individuals, termed functional compensation. The level of pollination per pollinator is quantified as the number of pollen grains deposited on a single flower by a single bee.


To investigate functional and numerical compensation of pollinators visiting watermelon (Citrullus lanatus), we will survey the diversity and abundance of bees visiting watermelon flowers at a sample of farms in the Delaware Valley and then quantify the number of pollen grains deposited on flowers by members of the most common bee species. Higher deposition by bees at low-diversity farms compared to low deposition by bees at high-diversity farms would indicate the occurrence of functional compensation. An increasing abundance of certain bee species coupled with decreasing diversity would indicate that numerical compensation is occurring. Either of these processes could be expected to buffer pollination function against a loss of bee diversity and abundance. Our results will contribute to understanding the mechanisms that determine the role of native biodiversity on crop pollination and provide key information to farmers and conservation managers in the region.

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