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RESEARCH ARTICLE
Contents Vol 61(1)

Biotic and abiotic determinants of intermediate-consumer trophic diversity in the Florida everglades

Brooke L. Sargeant A B , Evelyn E. Gaiser A and Joel C. Trexler A
+ Author Affiliations
- Author Affiliations

A Department of Biological Sciences and the Southeast Environmental Research Center, Florida International University, 11200 SW 8th St, Miami, FL 33199, USA.

B Corresponding author. Email: brooke.l.sargeant@gmail.com

Marine and Freshwater Research 61(1) 11-22 https://doi.org/10.1071/MF08322
Submitted: 25 November 2008  Accepted: 3 June 2009   Published: 29 January 2010

Abstract

Food-web structure can shape population dynamics and ecosystem functioning and stability. We investigated the structure of a food-web fragment consisting of dominant intermediate consumers (fishes and crayfishes) in the Florida Everglades, using stable isotope analysis to quantify trophic diversity along gradients of primary production (periphyton), disturbance (marsh drying) and intermediate-consumer density (a possible indicator of competition). We predicted that trophic diversity would increase with resource availability and decrease after disturbance, and that competition could result in greater trophic diversity by favouring resource partitioning. Total trophic diversity, measured by niche area, decreased with periphyton biomass and an ordination axis representing several bluegreen algae species. Consumers’ basal resource diversity, estimated by δ13C values, was similarly related to algal community structure. The range of trophic levels (δ15N range) increased with time since the most recent drying and reflooding event, but decreased with intermediate-consumer density, and was positively related to the ordination axis reflecting increases in green algae and decreases in filamentous bluegreen algae. Our findings suggest that algal quality, independent of quantity, influences food-web structure and demonstrate an indirect role of nutrient enrichment mediated by its effects on periphyton palatability and biomass. These results reveal potential mechanisms for anthropogenic effects on Everglades communities.

Additional keywords: competition, disturbance, food web, nutrients.


Acknowledgements

This work was made possible by Peter Kalla and Daniel Scheidt of the USA Environmental Protection Agency (US EPA), who managed this effort and by Jennifer Richards of Florida International University (FIU), who coordinated our research program and assured adequate funding and research support for this project. We thank Mike Cuoto, Albert Gonzales, Charles Molnar, Angela Marino, Christine Taylor and Franco Tobias for collecting and processing samples, Charles Goss for providing hydrological data, Aaron Parker for providing the map, and Clifton Ruehl and anonymous referees for helpful suggestions on this manuscript. This research was conducted as part of the US EPA’s (Region 4, Science and Ecosystem Support Division and Water Management Divison) R-EMAP project (EPA 904-R-07–001), which was jointly funded by the US EPA and the Everglades National Park (ENP) under cooperative agreement number H5297–05–0088 between FIU and ENP. This material is based upon work supported by the National Science Foundation under Grant No. DBI-0620409 and Grant No. DEB-9910514. This is contribution 427 of the South-east Environmental Research Center. We thank Everglades National Park and the Florida Game and Freshwater Fish Commission for issuing permits to sample fishes in the Everglades.


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