SPRING 2003

RESEARCH NEWS

COLLABORATIVE RESEARCH: RESPONSE OF TROPICAL STREAM ECOSYSTEM STRUCTURE AND FUNCTION TO AMPHIBIAN EXTINCTION

Project Summary: This interdisciplinary collaborative proposal, with investigators from 3 institutions, addresses central questions in ecosystem-level ecology that relate to the consequences of an extinction event. Catastrophic reductions in amphibian diversity and abundance in neotropical highlands represent important opportunities to simultaneously quantify the ecological significance of stream-dwelling anurans and assess the ecosystem-level consequences of their loss. The proposed research will assess changes in stream ecosystem structure and energy flow associated with the loss of stream-dwelling anurans. Intensive studies of ecosystem structure (primary producer and consumer diversity, trophic structure, organic matter resource quantity and quality) and function (primary and secondary production, respiration) will be performed at the reach scale for 2 years on 2 Panamanian highland streams with natural amphibian populations and 2 similar streams in a nearby region that has experienced recent extinctions. Stable isotope analyses (∂13C, ∂15N) of all major resource pools and consumer groups will be used in conjunction with these studies to construct quantitative food webs, and a series of smaller-scale studies (e.g., tadpole assimilation, gut analyses of consumer groups) and manipulations (tadpole exclusions) will also be performed to identify and quantify specific mechanisms underlying observed patterns. This series of intensive studies and manipulations will be performed to address the following questions:
_ How are amphibian declines in tropical highlands altering stream food webs; what are the specific influences on primary producers, detrital resources, and other consumer groups in streams?
_ What are the ecosystem-level consequences of dramatic declines in amphibian abundance and diversity in tropical highland stream and riparian habitats?
_ How will the reduction of riparian anurans influence energy subsidies in the form of amphibian biomass to riparian habitats and predators?

Based on preliminary studies in streams where amphibians have not declined, tadpoles are abundant and important grazers. As such, their loss should result in significant changes in stream ecosystem structure and function including potentially increased algal periphyton biomass, reduced biomass-specific primary production, reduced quantity and quality of fine particulate organic matter, and alterations in the relative importance of autochthonous and allochthonous energy flow pathways. Other predicted responses include changes in invertebrate community structure and production, and reductions in energy flow from streams to riparian habitats.

There are intensive efforts underway to identify the extent and cause of amphibian declines occurring throughout Central and South America and other regions including Australia. The focus of this proposal is to quantify the consequences of these events, regardless of the cause or causes. The investigators collected preliminary data from one of the few remaining highland regions in Central America that has not been affected (funded by an NSF-SGER grant), but there are strong indications that extinctions will occur there within the next few years, after which the opportunity to quantify impacts will be lost. Along with manipulative experiments, quantitative energy budgets for the 2 types of streams (pre and post amphibian extinctions) will be constructed and compared.

The intellectual merits of this research are that it will provide the first quantitative insight into the ecosystem-level consequences of these catastrophic events and the significance of tropical anurans to stream ecosystems. The broader implications of this research are that findings will be relevant to an urgent problem (i.e. amphibian declines) influencing many regions. The proposed 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 further collaboration between the 3 institutions involved and other scientists researching related issues in the tropics.

Dr. Catherine M. Pringle
Professor
http://www.arches.uga.edu/~cpringle/
Institute of Ecology
The University of Georgia
717A Bio. Sci. Bldg.
Athens, GA. 30602-2602
pringle@sparc.ecology.uga.edu
Phone: (706) 542-1120
Fax #: (706) 542-3344

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