Trophic niche dynamics of two fish mesoconsumers in adjacent coastal habitats with varying nutrient regimes.

Abstract

Changes of consumers' trophic niches, the n-dimensional biotic space that allows a species to satisfy its minimum requirements for population growth, are driven in part by shifts in the degree of individual resource use specialization within a population. Individual specialization results from complex trade-offs in inter- and intraspecific competition as organisms reduce niche overlap within a population or with heterospecifics. It is vital to build empirical knowledge on the trophic niche dynamics of consumers, given the role that niche dynamics play in food web stability, species coexistence, and population resilience, especially quantifying the trophic niche's expansion and contraction of coastal fish populations experiencing increasing frequency of environmental disturbance and habitat transformation. In coastal ecosystems, disturbances alter the connectivity, productivity, and nutrient regimes of aquatic habitats, which could lead to significant shifts in consumers' trophic niches. We investigated the trophic niche dynamics of two fish species Centropomus undecimalis (Common Snook) and Megalops atlanticus (Atlantic Tarpon), across two adjacent coastal lake systems of varying nutrient regimes (eutrophic vs. mesotrophic) and hydrological connectivity. In both systems, Snook had larger trophic niches than Tarpon. Also, the trophic niche size in the eutrophic system was larger than the mesotrophic system for both species. Snook and Tarpon used different prey resources, resulting in low niche overlap between species in both systems. Our results highlight how altered hydrological connectivity, and nutrient regimes can shift trophic niche dynamics of higher trophic-level consumers, likely due to changes in prey landscapes and shifts in the foraging ecology of species.