PARENT SESSION
Oral Session # 71: Trophic Structure I: Theory; Aquatic Systems.
Presiding: D Chalcraft
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 202.

A pre-extirpation study of the role of stream-dwelling frogs in neotropical foodweb dynamics.

Kilham, Susan^*,1, Pringle, Catherine², Lips, Karen³, Drake, Dana², Ranvestel, Anthony³, ¹ Department Bioscience & Biotechnology, Philadelphia, PA 19104, USA² Institute of Ecology, Athens, GA 30602³ Department of Zoology, Carbondale, IL 62901

ABSTRACT- Stable isotope analyses were used to examine trophic transfer in a neotropical montane stream characterized by abundant larval anurans. The goal was to assess the role of stream-dwelling frogs in food web dynamics before they become extirpated, as has already occurred in many regions throughout the neotropics. We selected a study site in the headwaters of the Rio Guabal in the Parque Nacional Omar Torrijos H., El Cope, Cocle, Panama. The site is ca. 700 masl on the Atlantic slope of central Panama, and is about 300 km east of the closest documented site of frog extirpations. Samples were collected from May to August, 2000. The ¹⁵N in the first and second trophic levels were a function of rainfall, decreasing as rainfall increased. Food web fractionation of ¹⁵N was much less on average (1.9‰per trophic step) in these tropical stream food webs than in well documented lake food webs (3.4‰). The ¹³C of autotrophs appeared to be affected by stream flow. Our results are important baseline data that will be used to make predictions regarding how trophic structure will change post-extirpation, which is apparently just beginning in this area.

Key words: neotropical foodwebs, frog extirpation, tropical streams, tadpoles