geer > 2000 > poster > trophic patterns in the everglades freshwater fish community across habitats and seasons
Trophic Patterns in the Everglades Freshwater Fish Community Across Habitats and SeasonsPoster presented December 2000, at the Greater Everglades Ecosystem Restoration Conference William F. Loftus1 and Joel C. Trexler2 [ Disclaimer ]
We described fish-diet differences across habitats and seasons by analyzing stomach contents of > 4,000 fishes of 32 native and introduced species. Major foods included periphyton, detritus/algae mix, small invertebrates, aquatic insects, decapods, and fishes. Florida gar, largemouth bass, pike killifish, and bowfin were at the top of the piscine food web. Using prey volumes, we grouped the fishes as herbivores, omnivores, or carnivores. Stable-isotope analysis gave an independent and similar assessment of trophic placement. Community trophic patterns were similar to those from tropical communities.
The trophic ecology of Everglades fishes is poorly documented. In tropical-fish communities, hydrologic seasonality greatly affects patterns of food-resource use, such as local and long-range movements among habitats, seasonal changes in diets, diet specializations, the presence and seasonality of diet overlaps, etc. (Lowe-McConnell 1975; Winemiller 1989, 1990). We analyzed Everglades native and introduced fish diets to identify the most important invertebrate and plant prey, and to compare trophic positions of species within and among three habitats and two seasons (Fig. 1). We used the complementary techniques of stomach and stable isotope analysis for both instantaneous and time-integrated views of animal diets (Vander Zanden and Rasmussen 1996).
We then compared diet patterns in the temperate Everglades fish community with those from seasonal aquatic systems in the tropics. We posed the following hypotheses in examining those patterns: Ho1: Herbivory and omnivory are common trophic states in the Everglades. Ho2: Seasonal changes in diets within a habitat are usual . Ho3: Specialization in diet is common; generalists are rare. Ho4: Diet overlap is highest during high-water periods when food is plentiful. This study is a first step in using data from across habitats and seasons for use in constructing a empirical food web for the Everglades marsh.
Trophic Classification
Ho1: Only a few species were strict herbivores, detritivores, or piscivores. Most were omnivores, and these included the most numerous species in the community (Fig. 2).
Ho2: Seasonal changes in diets within habitats occurred, as seen in the NonmetricMultiDimensional Scaling plots (Fig. 3), although membership in trophic classes did not shift much with season (Fig. 4). At low water, volumes of detritus increased in pond fish (Wilcoxon Z=0.283, p<0.05), and fish prey increased in spikerush fish (Z=2.24, p<0.05). Total food volume decreased in pond fish at low water (Z=2.31, p<0.025), but increased in sawgrass (Z=2.35, p<0.02).
Ho3: Everglades fishes focused on a few major prey, shown by low diet breadth (Fig. 5) (Levins B). B decreased in ponds between high and low water (Wilcoxon Z=2.55, p<0.01), but not in other habitats.
Ho4: Piankas Dietary overlap (aij ) within habitats between high- and low-water periods was generally low and communities did not differ significantly (Mantel test, p<0.001). However, some species /size classes within habitats had diets that were similar:
Does the Everglades system behave more like a temperate or a tropical wetland, based on its faunal and abiotic characteristics? Environmental periodicity driven by seasonal rainfall causes the Everglades to resemble tropical wetlands. Seasonal Patterns
Adams, S. M., B. L. Kimmel, and G. R. Plosky. 1983. Sources of organic matter for reservoir fish production: a trophic-dynamics analysis. Canadian Journal of Fisheries and Aquatic Sciences 40, 1480-1495. Lowe-McConnell, R. H. 1975. Fish communities in tropical freshwaters: their distribution, ecology, and evolution. Longman, Inc., New York. Vander Zanden, M. J., and J. B. Rasmussen. 1996. A trophic position model of pelagic food webs: impact on contaminant bioaccumulation in lake trout. Ecological Monographs 66: 451-477. Winemiller, K. O. 1989. Ontogenetic diet shifts and resource partitioning among piscivorous fishes in the Venezuelan llanos. Environmental Biology of Fishes 26: 177-199. Winemiller, K. O. 1990. Spatial and temporal variation on tropical fish trophic networks. Ecological Monographs 60: 331-367. Winemiller, K. O. 1996. Factors driving temporal and spatial variation in aquatic floodplain food webs, pages 298-312 IN G. A. Polis and K. O. Winemiller (Eds.). Food Webs: integration of patterns and dynamics. Chapman and Hall, New York. 472 p.
We could not have completed this study without the efforts of Victoria Foster and Jennifer Rehage, who assisted in summarizing the raw data for analysis and in preparing the report and poster. Tom Atkeson, FL DEP, provided funds that helped to complete the analysis. Support for the study was provided by: USGS-Biological Resources Division, U. S. National Park Service, Florida Department of Environmental Protection, Florida International University
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Related information: SOFIA Projects: Influence of Hydrology on Life-History Parameters of Common Freshwater Fishes from Southern Florida
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