NSF – TADS Project:

Collaborative Research (UGA, SIU & Drexel):
Ecosystem-level consequences of extinction: quantifying the ecological effects of catastrophic amphibian declines in neotropical streams.

 Tropical Amphibian Declines (TADS)

Location/Duration: Panama  (2007-2012)
UGA Graduate Student: Scott Connelly
Post-Doctoral Associate:  Piet Verburg

Summary: PIs: Matt Whiles and Karen Lipps (Southern Illinois University), Catherine Pringle (University of Georgia), and Susan Kilham (Drexel University)

This collaborative proposal addresses the ecological consequences of extinction and loss of biodiversity, one of the eight “grand challenges” and four focal areas of research in the environmental sciences recommended by the National Academy of Sciences’ National Research Council.  Disease-driven catastrophic amphibian declines in neotropical upland streams provide the rare opportunity to perform targeted studies to assess the ecological consequences of the loss of an entire group of consumers.  The proposed research builds on our prior comparisons of streams with and without amphibians and small-scale manipulation studies, which predict that amphibian losses will result in measurable changes in stream ecosystem structure and function.  Working on both sides of a moving disease front, we have been comparing streams in two upland sites in Panama, one that declined in 1998 (Fortuna) and one with intact amphibian communities (El Copé).  As predicted, El Copé was decimated by chytridiomycosis toward the end of our field studies, setting the stage for this renewal proposal.  We now have the unprecedented opportunity to quantify the ecological consequences of the loss of an entire group of consumers using comprehensive pre- and post-extirpation datasets from the same streams. We propose to quantify changes in ecosystem structure, including algal communities and biomass, macroinvertebrates, and food webs and riparian linkages, during a transitional phase (during and immediately following the die-off) and post-decline at El Copé.  We also propose a new series of investigations, focused explicitly on ecosystem processes and function, in streams ahead of the current disease front.  Intensive studies in these new streams, designed to build on what we’ve discovered thus far, will allow us to further quantify ecosystem responses to the loss of consumers.  In particular, we propose to use 15N tracer additions to model reach-scale N cycling before and after amphibian extirpations and to exclude tadpoles from half of a stream reach and measure ecosystem processes and stability with and without amphibians.  We will also test the generality of our results by sampling metrics of structure and function that are likely to reflect amphibian extirpations in a cross-section of pre- and post-decline streams, including a chronosequence of post-decline conditions.  Our overall prediction is that post-decline streams, with their reduced complexity and structure, will have reduced functioning and thus become replacement systems in an alternative state compared to those with amphibians.  The degree of functioning of post-decline streams will depend on the relative importance of tadpoles to ecosystem processes and the degree of functional redundancy in the system, both of which we will quantify.  We predict that these catastrophic losses, which occur over a relatively short time span, will not be compensated for through functional redundancy.   

Intensive efforts are underway to identify the causes and extent of amphibian declines occurring throughout the tropics.  The focus of our investigations is to quantify the ecological consequences of these extirpations, regardless of the cause or causes. The intellectual merits of this research are that we will gain quantitative insight into the effects of extinction and loss of biodiversity at multiple scales in natural systems.  Our proposed studies will assess relationships between consumer diversity and ecosystem function, the roles of consumers in top-down and bottom-up processes, and quantify the ecological roles of a poorly studied and imperiled group of consumers.  The broader implications are that findings will address pertinent questions regarding an urgent, global problem (amphibian declines).  A core component of the proposed research, the 15N tracer addition, will also integrate this project with a large-scale NSF-funded investigation on nutrient cycling in headwater streams through collaboration with PIs from the Lotic Intersite Nitrogen eXperiment (LINX) and use of LINX protocols in our study.  This research will also provide opportunities for students from Latin America and the U.S. to work on an important, large-scale environmental issue and will foster further collaboration among the 3 universities, the Smithsonian Tropical Research Institute, and others investigating related issues on amphibian declines in the tropics.

Publications:
Whiles,  M., K. Lips, C. Pringle, S. Kilham,  R. Bixby, R. Brenes, S. Connelly, J.  
        C. Colon-Gaud, M. Hunte-Brown, A. D. Huryn, C. Montgomery, and S. Peterson. 
        2006.  The effects of amphibian population declines to the structure and function of
        Neotropical stream ecosystems. Frontiers. 4(1): 27-34.
Ranvestel, A. W., K. R. Lips, C. M. Pringle, and M. R. Whiles.  2004.  Effects of
         grazing tadpoles on algae, sediments, and aquatic insects in a neotropical
         stream.  Freshwater Biology 49:274-285.

• Current Research Projects in Panama