Pollinator Losses and Plant Reproductive Function

Background/Question/Methods

Pollinator species are increasingly at risk of local and global extinction from human activities including; habitat loss, introduction of alien species, and global climate change. Insect-mediated pollination is a critically important ecosystem function because it is required for reproduction of nearly 90% of plant species in the world. Understanding how losses of pollinator species impact plant reproductive function is a question of key importance for the conservation of biodiversity and ecosystem function.

We examined the effects of pollinator species losses on plant reproduction using manipulative experiments, reducing pollinator diversity through temporary removals of targeted bee species in subalpine meadows in Colorado, USA.  We studied the effects of pollinator manipulations on reproductive success in four plant species from three plant families. We pre-bagged flower buds and opened mature bagged flowers for a standardized time period in both control and manipulated states.  We evaluated plant reproductive fitness by measuring stigmatic pollen deposition and seed production (including assessment of undeveloped seeds) within individual flowers as they developed into fruits.  We statistically controlled for changes in bee abundance (which could affect pollination) associated with the manipulations.

Results/Conclusions

While we will continue to gather and analyze data, preliminary results indicate: 1) increased deposition of heterospecific pollen on stigmas; and 2) reduction in relative seed set in manipulated vs. control states.  There was no significant effect of bee abundance in terms of these patterns.  These results may be driven by reductions in short-term foraging specialization by pollinators, a pattern that we have documented in this system.   This work contributes to a richer understanding of the complex community and ecosystem functional dynamics related to species losses.