Cascading Effects of Insect Pollinator Decline on Plant Functional Diversity in Urban Systems

Participants:  Dr. Daniel Bunker and Caroline DeVan, Federated Department of Biological Sciences Rutgers – Newark and NJIT

Status:  Began Spring 2010


Urbanization has profound effects on ecosystem services via habitat transformation, habitat fragmentation and environmental modification. These processes strongly affect plant and animal community composition by filtering out certain species while favoring others. For plant communities, the key filters include dispersal limitation, pollination limitation, and habitat (environmental) modification. Species that pass through these filters have traits that provide adaptation or tolerance to the urban environment, including the ability to disperse over long-distances and an adaptation for wind-pollination. Because these and many other traits are correlated within phenotypes, selection for these traits are likely to have unforeseen effects on additional traits resulting in additional declines in plant functional diversity in urban ecosystems. Studies have shown that while plant diversity and pollinator abundance both decline at the highest levels of urbanization, it is unclear whether there are few urban insect pollinated plants because there are so few urban insect pollinators or if there are so few insect pollinators because there are no plants to provide pollen.


The research we propose here will test the relative strength of the pollination and dispersal filters on plant and pollinator functional diversity. Our general hypothesis is that both dispersal and pollinator limitation remove a suite of individual species from urban systems and that this results in a loss of both species diversity and functional diversity in urban plant and pollinator communities. An increased understanding of the mechanisms controlling urban plant and pollinator biodiversity will lead directly to management techniques designed to promote and restore ecosystem function in urban areas.
Strategy & Activities:
We propose a series of pilot experiments that will compare the strength of both the dispersal and pollination filters at the species and community levels.
Project 1 – Baseline surveys of insect and plant biodiversity on early successional sites:
We will conduct baseline surveys of plant and insect community composition on a capped landfill and other sites within the Meadowlands. These surveys will inform our choice of plant and pollinator species as well as identify landfills and other potential sites for larger, future experiments.
Project 2 – Dispersal filter preliminary study:
We will establish a small replicated experiment to test dispersal effects on plant communities. Ten bee pollinated plant species will be added, via seed addition and transplantation, to plots where they do not currently exist. These experimental plots will be compared to controls where the plant species already exist. By quantifying seedling and transplant success we will determine whether dispersal limitation is controlling the distribution of these species.
We will also collect soil samples from each of our study sites. We will perform a seed bank study in the greenhouse and compare the seedlings that come up from the seed bank sample with the existing plant community at each site. This will allow us to know if there are species that are being dispersed to the site but are then unable to germinate and grow in the field.
Project 3 – Pollination filter preliminary experiment:
We will establish a small replicated experiment to test pollination limitation on several insect-pollinated plant species. For these species we will bag some plants to prevent pollination by insects, bag another set to prevent wind and animal pollination, leave some open to pollinators and hand-pollinate another set. Then we will determine whether there is a difference in seed set among these treatments. We will then compare the viability of these seeds in the greenhouse. This will also allow us to test for mixed mating systems (wind and animal pollination) in these plants.
– Baseline surveys of plant and insect communities on early successional sites within the Meadowlands
– Quantification of micro-site characteristics of these early successional sites
– Final report of our findings
– Publication in a peer-reviewed journal and presentations at scientific conferences