By eating and scaring prey, predators influence communities and ecosystems. In addition, some predators also physically alter habitats and recycle nutrients, which affect the resources available to autotrophs. These bottom-up effects could prove to be important for understanding food webs and how ecosystems function. American alligators (Alligator mississippiensis) engineer and maintain “ponds” in some marsh ecosystems that become hotspots of animal activity. We hypothesize that ponds have enhanced primary production and thus more algal- rather than detrital-based food webs compared to the marsh. Using a halo design, we sampled pond, near pond, and marsh habitats at ten sites in the 2018 wet and 2019 dry season. In each habitat, we collected flocculent detrital matter, floating and epiphytic periphyton, and emergent vascular and submerged non-vascular plants. We also used throw traps, minnow traps, drift fences, inverted funnel traps, dip nets, and electrofishing to collect aquatic consumers. We created composite samples on select producers, consumers, and detritus to run whole-cell fatty acid analyses. Using the profiles, we estimated proportion of poly-unsaturated (PUFA) compared to mono-unsaturated (MUFA) and saturated fatty acids (SAFA). PUFAs are commonly from autotrophic (e.g., algal) sources whereas MUFAs and SAFAs generally originate from heterotrophic bacteria and fungi.
Results/Conclusions
In 133 food web samples, we detected 121 different fatty acids. Across habitats, we found no differences in the proportion of fatty acid types in flocculent detrital matter (F2,36 = 2.16, p = 0.13) or periphyton (F2,23 = 0.21, p = 0.81). We observed no differences when comparing the fatty acid proportions between habitats for fish omnivores, Bluefin killifish (Lucania goodei; F2,18 = 1.23, p = 0.32) and Eastern mosquitofish (Gambusia holbrooki; F2,10 = 0.23, p = 0.80). The apparent lack of differences of the source of organic matter between marsh, near pond, and pond food webs may indicate their trophic connectivity. Future work may be able to determine the mechanism, but a focus on consumer movement patterns may be promising. Quantifying the effects and ecological importance of animal engineered ponds, especially by a large-bodied abundant predator, will advance the theoretical development of food web models by allowing multiple directions of trophic interactions (i.e., top-down and bottom-up processes). These efforts will also enhance our ability to predict the consequences ecosystem restoration and changes in hydrology.