Do Human-modified Landscapes Affect Solitary Bee Diversity, Foraging, and Reproduction in Northern Florida?

Do Human-modified Landscapes Affect Solitary Bee Diversity, Foraging, and Reproduction in Northern Florida?

Summary

Field work began in early Spring in North-central Florida (Alachua Co.). Early results indicate that the study farms support a variety of native bees. It’s also apparent that non-crop vegetation management varies considerably from strict adherence to mown grass to allowing wildflowers to grow in field margins and growing flowers as crops. I have collected more than 50 pollen plant and about 10 bee specimens with pollen to date and have begun processing these samples. Ten farms have been visited for data collection so far, and I will add more farms during the month of April.

Objectives/Performance Targets

Bee Foraging Habitat: I’m using quadrat sampling along transects to document the height structure, coverage, and composition of crop and non-crop vegetation on farms. Using the same methods I’ll also sample around the edges of the farms to gain information on local vegetation communities that are likely to provide local bee habitat.

Habitat and Landscape Effects on Bee Species Richness:
a) I’ve been unable to find sustainably managed farms located in the urban portion of the rural-urban gradient in the study area (as proposed). Therefore, I am re-apportioning my effort and increasing the number of farms I plan to use that are surrounded by the other two types of land uses (agricultural and natural) in order to detect landscape-level effects on bee community structure.
b) I have done an exhaustive literature survey this spring to determine how large my landscape buffers around sampling locations need to be. I have determined that for the species I am now finding in my samples, that the relevant buffers should be 250m, 500m, 750m, and 1km radius. Within these buffers I will assess land uses in ArcGIS for analysis of bee community structure. These buffers are smaller than originally proposed, but take into consideration the small average bee sizes (which relates to maximum travel ability in bees).

Bee Pollination Choices: I have begun to collect flower and bee samples from farms to assess the pollination choices of native bees. For example, I collected Southeastern blueberry bees (Habropoda laboriosa) was found pollinating Florida’s early-blooming highbush blueberries in April and also on multiple members of the Brassicaceae family left to bolt after last year’s harvest. I collected the flowers and the bees to confirm pollen pick-up from those plants. It is already apparent from processed samples that some native bees visit multiple pollen sources on foraging trips. Processing involves chemically stripping oils and internal protoplasm from pollen grains, darkening their color for better contrast, and making permanent slide mounts for identification.

Bee Reproduction: The majority of native bees are ground nesters (Michener 2007), and excavation of nests in not feasible for this study. I determined in preliminary sampling last year that cavity-nesting bees only use a small fraction of artificial nests set out in appropriate habitats in this area. Therefore, I have re-apportioned the effort proposed for this to include a greater focus on pollen sampling from captured bees.

Accomplishments/Milestones

Data collection for the project began in early March on ten sustainably-managed farms in Alachua County, Florida. Data from these farms show that all of them support native bee populations and wildflowers. I’ve processed bees and labeled them by location for later identification. I’ve collected flowers opportunistically and along vegetation transects, pressed, and identified to await lab processing for the pollen reference collection (a set of techniques I learned over the winter from a palynologist at the University of Florida Museum). As expected, bees collected in bee bowls (passive collectors using attractive colors and soapy water) are different species from the ones collected by hand off flowers. A portion of the hand-collected bees will be used for the pollen collection portion of the study. I am still contacting new farms to raise the sample size to between 15 and 20 farms. Data collection will continue into March of 2012.

• Bee bowls with mixed crops. Visibility to bees is key in deciding placement.

Impacts and Contributions/Outcomes

In light of the decline in honey bee populations in North America there is speculation about the ability of native bees to pollinate crops, possibly replacing or at least supplementing honey bee pollination services. This project looks at two critical questions: do native bees carry crop pollen, and is it local vegetation structure around farms or broader landscape context that has more effect on native bee populations and species richness on farms? The first question relates to native bees’ potential to pollinate crops and the second will provide basic information on whether on-farm vegetation management would be sufficient to support native bee communities. In other words, the results of this study should help farmers to know whether native bees are dependent on where their farms are located, how vegetation is managed on their farm, or some combination of the two.

Collaborators: