Modeling Species Distributions of Three Endemic Florida Panhandle Mints under Climate Change: Comparing Plant and Pollinator Distribution Shifts under Future Conditions
Climate change is expected to drive some species to extinction by restricting the range of their suitable habitat or by causing local extinctions of associated organisms necessary to the species' survival and reproduction. However, it is not yet widely appreciated that climate change might directly disrupt or eliminate beneficial ecological interactions between species even before extinctions occur. There is growing interest in utilizing species distribution models as management tools and for predicting changes under future conditions such as climate change (Peterson et al. 2000; Guisan and Thuiller 2005; Whittaker et al. 2005). It is important to develop knowledge about the ecological interactions and reproductive biology of species of conservation concern to inform long-term strategies for conservation under changing climatic conditions, particularly for rare and narrowly distributed species. The Florida Panhandle is home to many endemic plants, and many of these are rare and threatened within their range. Unfortunately, for many of these Panhandle endemics, little is known about their ecological interactions and reproductive biology. Here, I address this need with a two-part research project. The objectives of my research were to (1) observe and identify the potential pollinators of three mint species (Lamiaceae) endemic to the Florida Panhandle, (2) determine if these plants are self-compatible, and (3) predict the current and future areas of suitability for these mint species and their pollinators under a climate change scenario. I address three questions related to the last objective: (1) where are the plants and their pollinators expected to occur given current conditions? (2) where are the plants and their pollinators predicted to occur under future climate change conditions? and (3) do these future predicted suitable areas overlap? The three mint species I examined were Apalachicola false rosemary (Conradina glabra), Godfrey's false dragonhead (Physostegia godfreyi), and mock pennyroyal (Stachydeoma graveolens). I performed field observations of these endemic mints to identify the potential pollinators of the species. I also performed pollinator exclusion manipulations in two populations of two of the species to determine if they were self-compatible in the absence of pollinators. I found that all three species are visited by multiple potential pollinators, although the numbers and identities of potential pollinators differed between species (and to a smaller extent between populations). Most of the potential pollinators observed were native bees, but all were from genera that have fairly widespread distributions compared to those of the plants in this study. I determined that Conradina glabra and Physostegia godfreyi are self-compatible. A smaller percentage of flowers set seeds when pollinators were excluded from these species, but, when I hand-pollinated Conradina glabra, a percentage of flowers similar to the open pollinated treatment set seeds. I did not test the self-compatibility of Stachydeoma graveolens. I conclude from these results that the two examined species are self-compatible but likely rely on pollinators for maximum seed set. I selected three of the most frequent visitors to the three plant species, Xylocopa virginica, Anthophora abrupta, and Megachile species, to create species distribution models. I modeled the areas of suitability for these three mint species and the selected potential pollinators with current conditions and with future conditions in a doubled CO2 climate scenario. I used the Maxent modeling method (maximum entropy modeling) to create the models. The suitability maps were examined to see if separations in predicted ranges between plants and their potential pollinators might occur. Two of the three plant species, Stachydeoma graveolens and Physostegia godfreyi, had expanded future areas of suitability, whereas the area of suitability for Conradina glabra shrank and shifted more than 200 km. The models generated for all three mint species were accurate as determined using test data sampled from the presence records. The potential pollinators' areas of suitability were not modeled as well as those of the plants. However, the results suggest that these plant species will not be separated from their pollinators under this climate change scenario. This research represents a novel approach to conservation planning that considers both plants and their pollinators
Endemic Species, Pollinators, Species Distribution Modeling, Maxent, Climate Change
June 23, 2009.
A Thesis submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Austin Mast, Professor Directing Thesis; Alice A. Winn, Committee Member; Brian Inouye, Committee Member.
Florida State University
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