Research in the Williams Lab:



Erica Smith Haverford  '05
Rosemary Malfi Bryn Mawr '07
Daniela Miteva Bryn Mawr '07
Amanda Rahi Bryn Mawr '07

Effect of landscape change on pollinators and pollination

Pollination and Ecosystem Service


National Fish and Wildlife Foundation. Assessing and Restoring Native Crop Pollinators on Agricultural lands in New Jersey with C. Kremen and R. Winfree (Princeton)

NSF DEB #0516205 Collaborative Research: Community disassembly and ecosystem function: pollination services across agro-natural landscapes with C. Kremen

R. Winfree

Pollination is a key ecological function in natural systems. More than 70% of flowering plant species rely on animal pollinators, primarily bees, for sexual reproduction. Native bees also provide a potentially valuable service to humans in the form of crop pollination. If natural habitat is important for maintaining such native populations then pollination service may provide tangible incentives for the preservation of natural habitat. With students and collaborators, I am examining how isolation from natural habitat affects the pollination of crop by native bees.  We are also measuring the effect of landscape change on native plant reproduction in remaining semi-natural fragments of woodland.  This work explores potential community disassembly and whether it leads to loss of ecological function.  This research is one of two major efforts in our lab and has open opportunities for student projects.

Learn more about native bees and crop pollination in Pennsylvania and NJ

R Malfi collecting pollinator visitation data to tomato.  This summer R Malif (BMC '07) began investiagation of bumble bee communities in managed eastern meadows Flower on a stick. The method of following a bee with an unvisited flower on a long pole allows us to record the numbers of pollen grains deposited on the stigma of a flower by a bee during a single visit. Developed by J Thomson, U Toronto. Typical mosaic landscape along the Sacramento River composed of patches of remnant riparian forest and wash areas(dark green and gray streaks) surrounded by diverse agricultural fields

Dynamic pollination in desert communities

view Pollinator-plant interactions at San Bernardino MX view

Funding: National Science Foundation. DEB# 0418871 Contributions of Specialist pollinators to generalist plants: when do specialists matter? w/ R Minckley and T Roulston

Specialized “coevolutionary interaction” has long been a central tenet to hypotheses on the diversification of flowers. However, recent community studies of pollination interactions show that specialist pollinators commonly share host plants with numerous generalist pollinators, which may dilute their contribution to host plant pollination.  Only rudimentary information exists on the importance of specialist pollinators in these interactions, and under what circumstances, if any, they influence floral evolution. In this research our lab group along with RL Minckley (URochester) and TH Roulston (UVa), explore four predictions that could elevate the pollination contributions of specialists over generalists: 1) Specialists are better pollinators than generalists; 2) Specialists will show less seasonal and annual variation in abundance than generalists on the same host; 3) Generalists’ use of host plants will reflect plant species productivity at the community level, and 4) Specialists will be most important to the reproduction of their host when their host is a relatively poor resource provider in the community.


Our study areas are in the Chihuahuan Desert where approximately 40% of the 300+ bee species are floral specialists and 25+ plant species bloom at the same time within habitats. The extraordinarily rich diversity of specialist and generalist floral visitors, flowering plants, and interactions among them provides a unique opportunity to clarify how pollination relationships change in response to different levels of pollinator specificity in the community, environmental variation, and floral community dynamics.  This project also provides the opportunity for Bryn Mawr undergraduates to work with colleagues from other institutions in the USA and Mexico.


Pollination and restoration

Restoration efforts often focus on target "structural" plants such as trees, shrubs or dominant grasses and on specific animal species. Under such an approach the tacit assumption is that other components of the system and ecological processes will return on the coattails of the active restoration. I have been investigating whether such assumptions are met using a study system along the Sacramento River in California. Students and I have been collecting native bees and recording flower visitation in restored plots and remnants of native riparian forest to determine if pollinator communities and pollination are indeed restored through large scale planting efforts.

Differences in bee life-history are likely to affect whether they reestablish at such sites. Unique characteristics of bee foraging movement and the way they transfer pollen will contribute to their functional role as pollinators and could have significant effects on the persistence and the genetic structure of the restored plant populations as well as those in natural remnants.

One exciting bonus of this research program has been working with farmers, NGOs, and government agencies to understand their perspective and how their decisions affect the ecology and management of natural agricultural areas.


Pan-sampling of bees. This method uses colored bowls filled with soapy water to trap bees.


A sample of bees from a pan trap

Pollination Ecology and Pollen Dispersal

In another area of research I am using GMO Brassica napus (canola) plants to explore pollen transfer by different insect taxa. I adapted a transgenic pollen marker within canola that allowed me to track pollen grains from a specific plant to recipient flowers on other plants. In a simple sense, the grains from the transgenic plants are blue while those of other wild-type plants are yellow. This canola system allows detailed analysis of the mechanism behind pollen dispersal, but do these details apply to diverse natural systems where plants are visited by a diverse set of pollinators? Based on our experimental data colleagues and I are modeling pollen dispersal for situations involving different combinations of pollinators and are exploring on how the high variability inherent to the dispersal process affects overall patterns of mating for plants.


Transgenic pollen grains on a leg of the butterfly Pierisrapae.


Bumble bee (Bombus occidentalis) visiting B. napus

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Selected Publications:

            Williams, N. M. and C. Kremen (in press). Floral resource distribution among habitats determines productivity of a solitary bee, Osmia lignaria, in a mosaic    

            agricultural landscape. Ecological Applications.


            Ricketts, T., Williams, N. M. and  Mayfield, M. M. (2006) Connectivity and ecosystem services: crop pollination in agricultural landscapes In Connectivity

            Conservation. Crooks and Muttulingam (eds.)


            Larsen, T., Williams, N.M. and Kremen, C. 2005. Extinction order and altered community structure rapidly disrupt ecosystem functioning. Ecology Letters


Kremen, C. Williams, N. M., Bugg, R. L., Fay, J. P. and Thorp, R. W. 2004. The area requirements of an ecosystem service, crop pollination by native bee communities in California. Ecology Letters7:1109-1119.

Williams N. M. 2003. Use of novel pollen species by specialist and generalist solitary bees (Hymenoptera Megachilidae). Oecologia 134: 228-237.

Kremen, C., Williams, N. M. and Thorp, R. W. 2002. Crop pollination from native bees at risk from agricultural intensification. Proc. Nat. Acad. Sci. 99: 16812-16816

Williams N. M. and Tepedino, V. J. 2002. Consistent mixing of near and distant resources in foraging bouts by the solitary mason bee Osmia lignaria. Behav Ecol 14(1): 141-149

Williams, N. M., Minckley, R. L. Silveira, F. 2001. Demonstrating faunal changes in the face of natural variation in bees: the importance of baseline data. Cons. Ecology 5(1): 7. [online] URL: http://www.consecol.org/vol5/iss1/art7.

Harder, L. D., Williams, N. M., Jordan, C. Y, Nelson, W. 2001. The effects of floral design and display on pollinator economics and pollen dispersal. pp.297-317 In: Cognitive Ecology of Pollination, Chittka, L. & Thomson, J. D. (eds.) Cambridge University Press, Cambridge.

Williams, N. M. and Thomson, J. D. 2001. Pollinator quality in native bees and honey bees: comparing pollen removal and deposition on Phacelia tanacetifolia. In: Whence the pollinators of the future, Strickler and Cane (eds) Symp. Proceed. Entomol. Soc. Amer..

Williams, N. M. and Goodell, K. 2000. The association of nesting material and mandible shape in Osmia (Hymenoptera: Megachilidae): a morphometric analysis. Annals Entomol. Soc. Amer. 93(2):318-325.

Chittka, L., Williams, N. M., Rassmussen, H. and Thomson, J. D. 1999. Navigation without vision: bumblebee orientation in complete darkness. Proc. R. Soc. Lond. B. 226: 45-50.

Williams, N. M. and Thomson, J. D. 1998. Trapline foraging by bumble bees III. Temporal patterns of visitation and foraging success at single plants. Behav. Ecology 9 (6): 612-621.

Waser, N. M., Chittka, L., Price, M. V., Williams, N. M., Ollerton, J. 1996. Generalization in pollination systems and why it matters. Ecology 77(4): 1043-1060.

In prep

Greenleaf, S.A. , Williams, N.M., Winfree, R., Kremen, C.  Bee foraging ranges and their relationship to body size. (Submitted Oecologia, Sept 2006)

            Kremen, C., Williams, N. M. et al. Impact of land use change on pollinators: developing a conceptual framework for mobile-agent based ecosystem services

(Submitted Ecology Letters August 2006)

Williams, N. M., Richards, S. and Harder L. D. The importance of variation in pollen deposition for understanding plant mating patterns.

Williams, N. M. and Harder L. D. Comparison of pollen dispersal patterns by co-visiting pollinators

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