Indirect and direct controls of macroinvertebrates and small fish by abiotic factors and trophic interactions in the Florida Everglades

1. The roles of nutrients, disturbance and predation in regulating consumer densities have long been of interest, but their indirect effects have rarely been quantified in wetland ecosystems. The Florida Everglades contains gradients of hydrological disturbance (marsh drying) and nutrient enrichment (phosphorus), often correlated with densities of macroinvertebrate infauna (macroinvertebrates inhabiting periphyton), small fish and larger invertebrates, such as snails, grass shrimp, insects and crayfish. However, most causal relationships have yet to be quantified. 2.  We sampled periphyton (content and community structure) and consumer (small omnivores, carnivores and herbivores, and infaunal macroinvertebrates inhabiting periphyton) density at 28 sites spanning a range of hydrological and nutrient conditions and compared our data to seven a priori structural equation models. 3.  The best model included bottom-up and top-down effects among trophic groups and supported top-down control of infauna by omnivores and predators that cascaded to periphyton biomass. The next best model included bottom-up paths only and allowed direct effects of periphyton on omnivore density. Both models suggested a positive relationship between small herbivores and small omnivores, indicating that predation was unable to limit herbivore numbers. Total effects of time following flooding were negative for all three consumer groups even when both preferred models suggested positive direct effects for some groups. Total effects of nutrient levels (phosphorus) were positive for consumers and generally larger than those of hydrological disturbance and were mediated by changes in periphyton content. 4.  Our findings provide quantitative support for indirect effects of nutrient enrichment on consumers, and the importance of both algal community structure and periphyton biomass to Everglades food webs. Evidence for top-down control of infauna by omnivores was noted, though without substantially greater support than a competing bottom-up-only model.

Perceiving Spanish in Miami: The Interaction of Dialect and National Labeling

The current study implements a speech perception experiment that interrogates local perceptions of Spanish varieties in Miami. Participants (N=292) listened to recordings of three Spanish varieties (Peninsular, Highland Colombian, and Post-Castro Cuban) and were given background information about the speakers, including the parents’ country of origin. In certain cases, the parents’ national-origin label matched the country of origin of the speaker, but otherwise the background information and voices were mismatched. The manipulation distinguishes perceptions determined by bottom-up cues (dialect) from top-down ones (social information). Participants then rated each voice for a range of personal characteristics and answered hypothetical questions about the speakers’ employment, family, and income. Results show clear top-down effects of the social information that often drive perceptions up or down depending on the traits themselves. Additionally, the data suggest differences in perceptions between Hispanic/non-Hispanic and Cuban/non-Cuban participants, although the Cuban participants do not drive the Hispanic participants’ perceptions.