Abiotic factors influence the dynamics of marine habitat use by a highly mobile “freshwater” top predator
- 269 Downloads
Cross-ecosystem movements of mobile consumers are a primary mechanism by which energy and nutrients are exchanged between disparate ecosystems. While factors influencing variation in bottom–up subsidies between ecosystems have been well studied, much less is known regarding how biotic and abiotic factors influence the dynamics of mobile consumer-driven connectivity. In a literature survey, we found only 14% of studies examined factors contributing to variation in cross-ecosystem marine foraging by freshwater-adapted consumers. Here, we examine the relationships between abiotic factors and cross-ecosystem movements of a highly mobile freshwater-adapted top predator, Alligator mississippiensis (American alligator). As alligators lack physiological adaptations to survive in marine environments, we predict this linkage would be affected by factors that modify the ability to cope with high salinities. Our results reveal that multiple abiotic factors (e.g., relative humidity, temperature, total precipitation) are key explanatory variables of the duration of cross-ecosystem foraging trips by alligators, and that the absence of salt glands does not preclude them from performing long forays into marine environments. More broadly, our results expand our understanding of mobile consumer-driven ecosystem connectivity at the land–sea interface by demonstrating connectivity is highest when physical stressors are relaxed, and access to and availability of resources are maximized.
KeywordsAlligator mississippiensis Crocodilian Cross-ecosystem movement Ecosystem connectivity GPS–VHF telemetry Mobile consumer Trophic coupling
We thank R. Nifong, R. McNolty, M. Hensel, D. Penniman, R. McCarville, C. Conegemi, and C. Letcher for their assistance in field and with data processing. Special thanks are given to R. Nifong, J. Ferguson, and A. Rosenblatt for their comments on statistical analyses and on earlier drafts of this manuscript. This research was conducted under Georgia Department of Natural Resources Special Permits 29-WBH-08-178, 29-WBH-09-56, and 29-WBH-10-33 and University of Florida IACUC protocol 201005071. This research was supported by the Estuarine Reserves Division, Office of Ocean and Coastal Resource Management, National Ocean Service, and National Oceanic and Atmospheric Administration (Award No. NA10NOS4200022). This research was supported in part by the Georgia Coastal Ecosystems LTER Project (NSF Awards OCE-0620959 and OCE-1237140). Lastly, we thank the people of Sapelo Island, Georgia, and the Hog Hammock community for their support during this project.
- Barton, K., 2016. MuMIn: Multi-model inference (R package version 1.15.6) [available on internet at https://cran.r-project.org/package=MuMIn].
- Burnham, K. P. & D. R. Anderson, 2002. Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach. Springer, New York: 515.Google Scholar
- Craighead, F. C., 1968. The role of the alligator in shaping plant communities and maintaining wildlife in the southern Everglades. Florida Naturalist 41(67–74): 94.Google Scholar
- Davis, J. E., J. R. Spotila & W. C. Schefler, 1980. Evaporative water loss from the American alligator, Alligator mississippiensis: the relative importance of respiratory and cutaneous components and the regulatory role of the skin. Comparative Biochemistry and Physiology Part A: Comparative Physiology 67: 439–446.CrossRefGoogle Scholar
- Diebel, M., 2003. Morphology of meandering tidal channels on Sapelo Island. A report for Zoology 750-Problems in Oceanography. 19 pp.Google Scholar
- Estes, J. A., J. Terborgh, J. S. Brashares, M. E. Power, J. Berger, W. J. Bond, S. R. Carpenter, T. E. Essington, R. D. Holt, J. B. C. Jackson, R. J. Marquis, L. Oksanen, T. Oksanen, R. T. Paine, E. K. Pikitch, W. J. Ripple, S. A. Sandin, M. Scheffer, T. W. Schoener, J. B. Shurin, A. R. E. Sinclair, M. E. Soulé, R. Virtanen & D. A. Wardle, 2011. Trophic downgrading of planet Earth. Science 333: 301–306.CrossRefPubMedGoogle Scholar
- Fujisaki, I., K. M. Hart, M. S. Cherkiss, F. J. Mazzotti, J. S. Beauchamp, B. M. Jeffery & L. A. Brant, 2016. Spatial and temporal variability in estuary habitat use by American alligators spatial and temporal variability in estuary habitat use by American alligators. Estuaries and Coasts 39(5): 1561–1569.CrossRefGoogle Scholar
- GCE-LTER, 2014. Georgia coastal ecosystems long term ecological research: GCE-LTER project data [available on internet at https://gce-lter.marsci.uga.edu/public/data/data.htm].
- Gelman, A., & Y. -S. Su, 2016. Arm: Data analysis using regression and multilevel/hierarchical models [available on internet at https://cran.r-project.org/package=arm].
- Joanen, T. & L. McNease, 1970. A telemetric study of nesting female alligators on Rockefeller Refuge, Louisiana. Proceedings of the Annual Conference of Southeastern Association of Fish and Wildlife Agencies 24: 249–265.Google Scholar
- Joanen, T. & L. McNease, 1972. A telemetric study of adult male alligators on Rockefeller Refuge, Louisiana. Proceedings of the Annual Conference of Southeastern Association of Fish and Wildlife Agencies 26: 252–275.Google Scholar
- Kay, W. R., 2004. A new method for attaching electronic devices to crocodilians. Herpetological Review 35: 354–357.Google Scholar
- Madden, M., T. R. Jordan, L. Chafin, A. Gaddis, C. Jordan, J. Masour, A. Parker & A. Wahid, 2014. Habitat and Land Cover Map of Sapelo Island, Center for Geospatial Research (CGR). Department of Geography, University of Georgia, Athens.Google Scholar
- McNease, L. & T. Joanen, 1977. Alligator diets in relation to marsh salinity. Annual Meeting of the Southeastern Association of Game and Fish Commissioners 31: 36–40.Google Scholar
- Messel, H., G. C. Vorlicek, G. A. Wells, & W. J. Green, 1981. Monograph 1. Surveys of the tidal systems in the Northern Territory of Australia and their crocodile populations. The Blyth-Cadell River Systems Study and the Status of Crocodylus porosus populations in the tidal waterways of Northern Australia. Pergamon Press, Rushcutters Bay, New South Wales: 454–459.Google Scholar
- Messel, H., G. C. Vorlicek, G. A. Wells, & W. J. Green, 1982. Status and dynamics of Crocodylus porosus populations in the tidal waterways of northern Australia. International Union for Conservation of Nature and Natural Resources (IUCN) Publication Supplement Paper: 46 pp.Google Scholar
- Nifong, J. C., 2016. Living on the edge: trophic ecology of Alligator mississippiensis (American alligator) with access to a shallow estuarine impoundment. Bulletin of the Florida Museum of Natural History 54: 13–49.Google Scholar
- Peckarsky, B. L., P. A. Abrams, D. I. Bolnick, L. M. Dill, J. H. Grabowski, B. Luttbeg, J. L. Orrock, S. D. Peacor, E. L. Preisser, O. J. Schmitz & G. C. Trussell, 2008. Revisiting the classics: considering non-consumptive effects in textbook examples of predator-prey interactions. Ecology 89: 2416–2425.CrossRefPubMedGoogle Scholar
- R Core Development Team, 2013. R: A language and environment for statistical computing. [available on intenet at http://www.r-project.org/].
- Ross, C. A., & C. H. Ernst, 1994. Alligator mississippiensis (Daudin) American Alligator. Catalogue of American Amphibians and Reptiles 600: 1–14.Google Scholar
- Rosenblatt, A. E., M. R. Heithaus, F. J. Mazzotti, M. Cherkiss & B. M. Jeffery, 2013b. Intra-population variation in activity ranges, diel patterns, movement rates, and habitat use of American alligators in a subtropical estuary. Estuarine, Coastal and Shelf Science 135: 182–190.CrossRefGoogle Scholar
- Rosenblatt, A. E., J. C. Nifong, M. R. Heithaus, F. J. Mazzotti, M. S. Cherkiss, B. M. Jeffery, R. M. Elsey, R. A. Decker, B. R. Silliman, L. J. Guillette, J. Russell & H. L. Justin, 2015. Factors affecting individual foraging specialization and temporal diet stability across the range of a large “generalist” apex predator. Oecologia 178: 5–16.CrossRefPubMedGoogle Scholar
- Signer, J. & N. Balkenhol, 2015. Reproducible home ranges (rhr): A new, user‐friendly R package for analyses of wildlife telemetry data. Wildlife Society Bulletin 39(2): 358–363 [available on internet at https://cran.r-project.org].
- Skaug, H., D. Fournier, B. Bolker, A. Magnusson & A. Nielsen, 2014. Generalized linear mixed models using AD model builder. R Statistical Program [available on internet at https://cran.r-project.org].
- Tamarack, J. L., 1989. Georgia’s coastal island alligators, variations and habitat and prey availability. Proceedings of the Eighth Working Meeting of the Crocodile Specialist Group: 105–118.Google Scholar
- Taplin, L. E., G. C. Grigg, P. Harlow, T. M. Ellis & W. A. Dunson, 1982. Lingual salt glands in Crocodylus acutus and C. johnstoni and their absence from Alligator mississippiensis and Caiman crocodilus. Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 149: 43–47.CrossRefGoogle Scholar
- Wilkinson, P. M. & W. E. Rhodes, 1992. Nesting habitat of american alligators in coastal South Carolina. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife agencies 46: 260–265.Google Scholar