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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2014)

Background

Urbanization and agricultural intensification of landscapes are influential drivers of global change, resulting in direct impacts on ecological communities and leading to shifts in species distributions and interactions. These landscapes are novel for many reasons, but an often overlooked aspect is how the phenology of vegetation can vary between land use types. Because such differences can impact floral-dependent species, I explored how human-altered landscapes affect bees, a group of high economic and ecological importance. I measured the phenological diversity of vegetation across a human-altered landscape, compared these findings to a spatio-temporal pollinator distribution dataset, and investigated how pollinator visitation translates to seed set.

Approach

I collected and observed bees for three field seasons in a peri-urban landscape on the outskirts of the San Francisco Bay Area, California, where urban, agricultural, and natural land use types interface. To assess patterns of phenological change, I used seasonal remote sensing data from MOD13Q1 vegetation indices, which I complimented with collections of 91 bee species groups across different land use types. I examined how differences in bee populations between land use types impacted plant-pollinator interactions by making standardized observations of floral visitation and measuring seed set of yellow starthistle (Centaurea solstitialis), a common grassland invasive abundant in all land use types.

Results & Conclusion

I found phenological patterns in vegetation indices, total bee abundance, and species richness of human-altered landscapes to be out of sync between urban, agricultural, and natural areas. Vegetation indices were significant predictors of total bee abundance, a relationship that improved when time lags were included. Bee visitation was highest in urban and agricultural land use contexts, but seed set rates in these human-altered landscapes were lower than in natural sites. These results emphasize the importance of differences in temporal dynamics between land use types, a previously overlooked mechanism of global change.

    Cover page: Bees in a Changing World: How land surface phenology, bee community distributions, and pollinator-plant interactions are impacted by urbanization and agriculture
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2015)
    Global change has led to shifts in phenology, potentially disrupting species interactions such as plant-pollinator relationships. Advances in remote sensing techniques allow one to detect vegetation phenological diversity between different land use types, but it is not clear how this translates to other communities in the ecosystem. Here, we investigated the phenological diversity of the vegetation across a human-altered landscape including urban, agricultural, and natural land use types. We found that the patterns of change in the vegetation indices (EVI and NDVI) of human-altered landscapes are out of synchronization with the phenology in neighboring natural California grassland habitat. Comparing these findings to a spatio-temporal pollinator distribution dataset, EVI and NDVI were significant predictors of total bee abundance, a relationship that improved with time lags. This evidence supports the importance of differences in temporal dynamics between land use types. These findings also highlight the potential to utilize remote sensing data to make predictions for components of biodiversity that have tight vegetation associations, such as pollinators.
      Cover page: Remote sensing captures varying temporal patterns of vegetation between human-altered and natural landscapes
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2014)
      Pollinator-plant relationships are found to be particularly vulnerable to land use change. Yet despite extensive research in agricultural and natural systems, less attention has focused on these interactions in neighboring urban areas and its impact on pollination services. We investigated pollinator-plant interactions in a peri-urban landscape on the outskirts of the San Francisco Bay Area, California, where urban, agricultural, and natural land use types interface. We made standardized observations of floral visitation and measured seed set of yellow starthistle (Centaurea solstitialis), a common grassland invasive, to test the hypotheses that increasing urbanization decreases 1) rates of bee visitation, 2) viable seed set, and 3) the efficiency of pollination (relationship between bee visitation and seed set). We unexpectedly found that bee visitation was highest in urban and agricultural land use contexts, but in contrast, seed set rates in these human-altered landscapes were lower than in natural sites. An explanation for the discrepancy between floral visitation and seed set is that higher plant diversity in urban and agricultural areas, as a result of more introduced species, decreases pollinator efficiency. If these patterns are consistent across other plant species, the novel plant communities created in these managed landscapes and the generalist bee species that are favored by human-altered environments will reduce pollination services.
        Cover page: Pollinator interactions with yellow starthistle (Centaurea solstitialis) across urban, agricultural, and natural landscapes.
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2014)
        Pollinator-plant relationships are found to be particularly vulnerable to land use change. Yet despite extensive research in agricultural and natural systems, less attention has focused on these interactions in neighboring urban areas and its impact on pollination services. We investigated pollinator-plant interactions in a peri-urban landscape on the outskirts of the San Francisco Bay Area, California, where urban, agricultural, and natural land use types interface. We made standardized observations of floral visitation and measured seed set of yellow starthistle (Centaurea solstitialis), a common grassland invasive, to test the hypotheses that increasing urbanization decreases 1) rates of bee visitation, 2) viable seed set, and 3) the efficiency of pollination (relationship between bee visitation and seed set). We unexpectedly found that bee visitation was highest in urban and agricultural land use contexts, but in contrast, seed set rates in these human-altered landscapes were lower than in natural sites. An explanation for the discrepancy between floral visitation and seed set is that higher plant diversity in urban and agricultural areas, as a result of more introduced species, decreases pollinator efficiency. If these patterns are consistent across other plant species, the novel plant communities created in these managed landscapes and the generalist bee species that are favored by human-altered environments will reduce pollination services.
          Cover page: Pollinator Interactions with Yellow Starthistle (Centaurea solstitialis) across Urban, Agricultural, and Natural Landscapes
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2016)
          Urbanization and agricultural intensification of landscapes are important drivers of global change, which in turn have direct impacts on local ecological communities leading to shifts in species distributions and interactions. Here, we illustrate how human-altered landscapes, with novel ornamental and crop plant communities, result not only in changes to local community diversity of floral-dependent species, but also in shifts in seasonal abundance of bee pollinators. Three years of data on the spatio-temporal distributions of 91 bee species show that seasonal patterns of abundance and species richness in human-altered landscapes varied significantly less compared to natural habitats in which floral resources are relatively scarce in the dry summer months. These findings demonstrate that anthropogenic environmental changes in urban and agricultural systems, here mediated through changes in plant resources and water inputs, can alter the temporal dynamics of pollinators that depend on them. Changes in phenology of interactions can be an important, though frequently overlooked, mechanism of global change.
            Cover page: Temporal dynamics influenced by global change: bee community phenology in urban, agricultural, and natural landscapes
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