Anthropogenic Influence on the Land Snail Community of the Canary Islands Alexander F. Wall, June 13
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Bellwether of the Canaries: Anthropogenic influence on the land snail community of the Canary Islands Alexander F. Wall, June 13, 2016 B.S., University of Iowa, 2007 B.A., University of Iowa, 2007 A thesis submitted to the Graduate School of the University of Cincinnati in partial fulfillment for the degree of Master of Science in the Department of Geology of the College of Arts and Sciences by July 2016 Name of committee chairs: Dr. Yurena Yanes Dr. Arnold I. Miller Committee member: Dr. Joshua Miller Abstract In many parts of the world, human activities are now commensurate with natural environmental factors in governing the distributions and abundances of species. Natural areas near human-modified landscapes experience pollution, fragmentation, water diversion, introduced species, and other factors that may affect local biodiversity. The land snails of the Canary Islands provide excellent opportunities to diagnose the importance of anthropogenic agents in mediating the diversity and distribution of species. Land snails are particularly sensitive to disturbance and are an integral part of terrestrial ecosystems. This study analyzed the distributions and abundances of land snail subfossils at 60 localities throughout the Canary Islands coastal scrub biome. This was accomplished using data on natural and anthropogenic variables to assess their relative importance in governing land-snail diversity. A total of 34,801 dead shells represent a diverse malacofauna with highly localized endemism. A novel combination of analytical methods was able to distinguish the impact of anthropogenic factors on native land-snail diversity at the biome scale. Regression tree analyses indicated that diversity decreased with increased proximity to agricultural sites and airports — the latter taken as a proxy for heavily urbanized areas. Sites varied in biodiversity, e.g. from an average of 3.6 species in sites nearest human-modified areas, to an average of 6.9 species in the most remote sites. Impacts from modified areas affected natural areas at distances from ~8 km to less than 0.1 km away. Protected coastal scrub areas ii near human-modified landscapes may not, therefore, be effectively protecting some members of their constituent communities. iii iv Acknowledgements This research was funded by the following grants: The Geological Society of America Graduate Student Research Grant, The Conchologists of America Academic Grant, and the Society for Sedimentary Geology Student Assistance Grant. Thank you to the government of the Canary Islands for permitting the collection of the samples that are the foundation of this research. I would like to thank my advisors Yurena Yanes and Arnold I. Miller for their advice, support, and assistance in the field, laboratory, and classroom. Together, they and my fellow graduate student Elizabeth Bullard contributed the majority of specimens analyzed in this thesis and provided feedback and fresh ideas for every step in that analysis. Fellow graduate student Elizabeth Hausner helped plan the fieldwork while simultaneously teaching me the GIS skills I would make extensive use of in the production of this thesis. My third committee member, Dr. Joshua Miller introduced me to R and has provided constant support, both technical and theoretical, throughout the project. Special thanks go to Miguel Ibañez and Maria R. Alonso (Universidad de La Laguna) for their assistance with some land snail species identifications. v Table of contents Acknowledgements ................................................................................................ ii Table of contents .................................................................................................. vi Abstract .................................................................................................................. ii Introduction ........................................................................................................... 1 Field methods ....................................................................................................... 5 Statistical Methods .............................................................................................. 10 Results ................................................................................................................ 13 Land snails species composition and distribution .................................... 13 Environmental factors controlling biodiversity .......................................... 22 Discussion ........................................................................................................... 25 Conclusions ........................................................................................................ 31 References .......................................................................................................... 23 Supplemental Material .......................................................................................... 1 List of Figures Figure 1. Geographical location of the Canary Archipelago ............................................. 7 Figure 2. Rarefaction curves of each site ....................................................................... 15 Figure 3. Rarefied richness of land snails by site ........................................................... 20 Figure 4. Evenness of snails by site ............................................................................... 21 Figure 5. A three dimensional NMDS ............................................................................. 22 Figure 6 Regression tree of land snail richness .............................................................. 23 vi Figure 7. Regression tree of land snail Shannon diversity .............................................. 24 Figure 8. Regression tree of land snail Simpson diversity .............................................. 25 Table 1. Summary of measured environmental factors ................................................... 9 Table 2. Summary of land snail species per island ......................................................... 16 Table 3. Summary of endangered species ..................................................................... 17 Supplementary Materials: Figures Figure SM 1. Map of field sites ......................................................................................... 1 Figure SM 2. Boxplot showing richness grouped by Otala lactea ..................................... 5 Figure SM 3. Richness regression tree first split .............................................................. 6 Figure SM 4. Richness regression tree second split ......................................................... 7 Figure SM 5. Richness regression tree pruning parameters ............................................ 8 Figure SM 6. Shannon diversity regresiion tree first split .................................................. 9 Figure SM 7. Shannon divesity regression tree second split .......................................... 10 Figure SM 8. Shannon diversity regression tree pruing parameters ............................... 11 Figure SM 9. Simspon diversity regression tree first split ............................................... 12 Figure SM 10. Simpson divesity regression tree second split ........................................ 13 Figure SM 11. Simpson diversity regression tree pruning parameters ........................... 13 vii Figure SM 12. Detailed map of El Hierro land cover and sites with 1 km buffers. .......... 14 Figure SM 13. Detailed map of Fuerteventura land cover and sites with 1 km buffers. .. 15 Figure SM 14. Detailed map of Gran Canaria land cover and sites with 1 km buffers. .. 16 Figure SM 15. Detailed map of La Gomera land cover and sites with 1 km buffers. ...... 17 Figure SM 16. Detailed map of Lanzarote land cover and sites with 1 km buffers. ........ 18 Figure SM 17. Detailed map of La Palma land cover and sites with 1 km buffers. ......... 19 Figure SM 18. Detailed map of Tenerife land cover and sites with 1 km buffers. ........... 20 Supplementary Materials: Tables Table SM 1. Species counts ............................................................................................. 1 Table SM 2. Results of rarefaction .................................................................................. 20 Table SM 3 Hill Numbers Example ................................................................................. 22 viii Introduction Anthropogenic landscape modification has unintended ecological consequences for organisms in the modified areas (Fischer and Lindenmayer 2007 and sources cited therein). Crops, buildings, infrastructure, etc. replace natural biomes (the coexisting organisms in an area of similar environmental conditions). Yet these anthropogenic landscapes also create a halo of impact around the modified area through pollution, dispersal obstruction, water diversion, introduced species, and other factors (Wood et al. 2000). Quantifying the degree to which anthropogenic activities impact the biodiversity of nearby natural biomes, and the reach of these impacts, is critical to successful conservation initiatives. Discriminating between natural and anthropogenic agents in any ecosystem is not without its challenges. Historical records of biodiversity predating human modification tend to be rare and incomplete, so information on pre-disturbance baselines is rare. As an alternative, substituting space for time has met with success in some studies that compare community