Metadata

Description
Field collections

Fishes and invertebrates analyzed for this project were collected between 1977 and 1994. Most specimens (> 90%) were collected between 1977 and 1981, but supplemental collections were taken from the same study area at the same time of year during the mid-1990s to increase sample sizes for less common species, mainly larger predators. Collections in the mid-1990s included non-native species that had colonized the Everglades (see Kline et al., 2014 for timeline), and all specimens for stable-isotope analysis. Wet-season samples were collected between January and early March, and dry-season samples in April. Most fishes were collected with 5% rotenone solution (Nox- Fish®), along with electrofishing, cast nets, dip nets, and angling. All fishes were preserved in 10% buffered formalin and transferred to 70% ethanol, except those captured for isotopic analysis, which were euthanized with MS-222 and frozen. In total, we collected 3509 individuals from thirty-two species, of which 600 had empty stomachs (see Arrington et al., 2002). We analyzed stomach contents for the remaining 2909 fishes, 83% of those collected. The target sample size was twenty-five individuals per species size class per habitat-season level and the average was sixteen.

Laboratory analyses

We separated species into body-size groups based on length, termed species size classes, to examine the role of ontogeny in trophic resource partitioning within and among species, because most fishes undergo a change in diet with growth (Wainwright and Richard, 1995). We recorded the length and wet mass of each specimen before removing the stomach. In species without defined stomachs, we removed the digestive tract from the esophagus to the first bend in the tract. Each stomach was flushed of contents which were examined with a Wild®5A dissecting microscope and identified to the lowest-level taxon possible. Fragmented remains of insects, fishes, and crustaceans were termed “unidentifiable.” Insect taxa are larval forms, unless otherwise indicated. The number of individuals per prey type were recorded for individual consumers (Hyslop, 1980). For stable-isotope samples, we dissected muscle from small fishes and invertebrates for drying at 50°C, then pulverized it (Fry, 2006). Samples of major primary producers were dried and powdered after being acid-washed in HCl before drying to remove carbonates. Three to five individuals were analyzed to produce a mean value per taxon. The samples were analyzed shortly thereafter in the mid-1990s at the University of Georgia Institute of Ecology isotope laboratory. The isotopic standards used for δ13C and δ15N were Pee Dee Belemnite (PDB) and air, respectively. Average isotopic error of replicate standards was δ15N ≤ 0.2 ‰ and δ13C ≤ 0.1 ‰.



References:

Arrington, D. A., Winemiller, K. O., Loftus, W. F., & Akin, S. (2002). How often do fishes “run on empty”?. Ecology, 83(8), 2145-2151.

Fry, B. (2006). Stable isotope ecology (Vol. 521, p. 318). New York: Springer.

Hyslop, E. J. (1980). Stomach contents analysis—a review of methods and their application. Journal of fish biology, 17(4), 411-429.

Kline, J. L., Loftus, W. F., Kotun, K., Trexler, J. C., Rehage, J. S., Lorenz, J. J., & Robinson, M. (2014). Recent fish introductions into Everglades National Park: an unforeseen consequence of water management?. Wetlands, 34, 175-187.

Wainwright, P. C., & Richard, B. A. (1995). Predicting patterns of prey use from morphology of fishes. Environmental biology of fishes, 44, 97-113.