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.
Piscivore exclusion experiments predict impacts of commercial fishing on fish assemblages in tropical river lagoons.
Layman, Craig*,1, Winemiller, Kirk1, 1 Texas A & M University, College Station, TX, 77843-2258
ABSTRACT- Mediating effects of over-harvesting top predators depends on a clear understanding of how species interactions propagate through ecological communities. Due to complex direct and indirect interactions among species, such effects are especially difficult to predict in species-rich communities. Characteristics used to group species, and thus generalize ecological interactions, can aid in constructing predictive models in speciose food webs. We have demonstrated how size could be used to predict a trait-mediated response of multiple prey species (n>50) to piscivore (n>8) exclusion in the Cinaruco River, a lowland neotropical river. Here we review results of our small-scale experiments, and examine if they can be scaled up to predict larger-scale effects of commercial fishing. Lagoons (1-30 km2) are dispersed throughout the Cinaruco River floodplain landscape, and many are exploited by commercial netters. This results in a large-scale pattern in which some lagoons support robust populations of large-bodied piscivores (e.g., piranha and peacock cichlids), whereas others have had piscivore populations greatly reduced. Fish assemblages in netted lagoons are dominated by relatively larger prey fishes (> 40 mm), including Moenkhausia af lepidura and Bryconops caudomaculatus, the two species that responded most significantly in piscivore exclusion experiments. Assemblages in un-netted lagoons are dominated by a group of smaller (< 40 mm) species, none which were found to respond to piscivore exclusion. Results of extensive stomach content analyses (n>3,500) revealed prey fishes >40 mm were the most common prey of piscivorous fishes (i.e., those piscivores targeted by netters), providing additional evidence that observed differences are due to piscivore removal. Together, these results suggest (1) removal of piscivores has significant cascading effects on fish assemblages, and (2) prey size, as was demonstrated in exclusion experiments, can be used to predict large-scale assemblage patterns in a speciose tropical river food web.
Key words: trait-mediated indirect effect, size-selective predation, trophic cascade, food webs