Wednesday, May 28, 2008 - 10:15 AM
373

Use of a 15N tracer addition to assess the ecosystem-level significance of amphibians and their extirpations in neotropical headwater streams

Matt R. Whiles1, P. Verburg2, Walter K. Dodds3, Robert O. Hall Jr.4, Alexander D. Huryn5, S. S. Kilham6, K. R. Lips1, C. M. Pringle2, S. Connelly2, E. Griffith7, and H. Ross8. (1) Department of Zoology and Center for Ecology, Southern Illinois University, Carbondale, IL 62901-6501, (2) Odum School of Ecology, University of Georgia, Athens, GA 30602-2202, (3) Division of Biology, Kansas State University, 104 Ackert Hall, Manhattan, KS 66506, (4) Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, (5) Department of Biological Sciences, University of Alabama, Box 870206, Tuscaloosa, AL 35487, (6) Department of Biosciences and Biotechnology, Drexel University, Philadelphia, PA 19104-2875, (7) Smithsonian Tropical Research Institute, Panama, (8) El Valle, Panama

As part of the Tropical Amphibian Declines in Streams (TADS) project, we used a 15NH4 tracer addition in a Panamanian headwater stream to quantify the relative contributions of stream-dwelling tadpoles to N cycling and retention.  The study stream initially had an abundant and diverse assemblage of tadpoles in early 2006 (~10 species; 425 habitat-weighted mg dry mass m-2), but was located just ahead of a moving disease front linked to catastrophic amphibian declines that hit later that year.  Standing stocks, turnover, and fluxes of N in basal resources and common consumers (tadpoles, fish, macroinvertebrates) were quantified.  Total N uptake by primary consumers was 140 mg N m-2 d-1.  Grazing invertebrates and tadpoles accounted for ~10% of N uptake by primary consumers, and, based on N uptake, tadpoles were the 2nd most important grazers in the system.  Tadpoles had one of the slowest turnover rates of all consumers in the system (0.04 d-1 or 34 d), and are larger and less susceptible to predation.  Hence, tadpoles retain N compared to smaller grazers with much higher turnover and greater predation rates (e.g., leptophlebiid mayflies [0.87 d-1]).  Results suggest that ongoing catastrophic amphibian declines may alter N cycling patterns in headwater streams.


Web Page: amphibian, tropical, nitrogen

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