Community structure affects trophic ontogeny in a predatory fish.

Javier Sánchez‐Hernández,Antti P Eloranta,Per‐Arne Amundsen,Anders G Finstad

doi:10.1002/ece3.2600

Abstract

While most studies have focused on the timing and nature of ontogenetic niche shifts, information is scarce about the effects of community structure on trophic ontogeny of top predators. We investigated how community structure affects ontogenetic niche shifts (i.e., relationships between body length, trophic position, and individual dietary specialization) of a predatory fish, brown trout (Salmo trutta). We used stable isotope and stomach content analyses to test how functional characteristics of lake fish community compositions (competition and prey availability) modulate niche shifts in terms of (i) piscivorous behavior, (ii) trophic position, and (iii) individual dietary specialization. Northern Scandinavian freshwater fish communities were used as a study system, including nine subarctic lakes with contrasting fish community configurations: (i) trout‐only systems, (ii) two‐species systems (brown trout and Arctic charr [Salvelinus alpinus] coexisting), and (iii) three‐species systems (brown trout, Arctic charr, and three‐spined sticklebacks [Gasterosteus aculeatus] coexisting). We expected that the presence of profitable small prey (stickleback) and mixed competitor–prey fish species (charr) supports early piscivory and high individual dietary specialization among trout in multispecies communities, whereas minor ontogenetic shifts were expected in trout‐only systems. From logistic regression models, the presence of a suitable prey fish species (stickleback) emerged as the principal variable determining the size at ontogenetic niche shifts. Generalized additive mixed models indicated that fish community structure shaped ontogenetic niche shifts in trout, with the strongest positive relationships between body length, trophic position, and individual dietary specialization being observed in three‐species communities. Our findings revealed that the presence of a small‐sized prey fish species (stickleback) rather than a mixed competitor–prey fish species (charr) was an important factor affecting the ontogenetic niche‐shift processes of trout. The study demonstrates that community structure may modulate the ontogenetic diet trajectories of and individual niche specialization within a top predator.

Highlights

Ontogenetic changes in ecological processes are widespread across the animal kingdom, and they are central to understand ecosystem functioning (Nakazawa, 2015; Woodward et al, 2005)
Interspecific interactions often play a key role in structuring communities, and these relationships are commonly influenced by ontogenetic niche shifts (Werner, 1986; Werner & Gilliam, 1984)
It has remained unexplored how local community structure shapes the relationships between ontogenetic niche shifts and individual diet variation

Summary

| INTRODUCTION

Ontogenetic changes in ecological processes are widespread across the animal kingdom, and they are central to understand ecosystem functioning (Nakazawa, 2015; Woodward et al, 2005). The recent study by Svanbäck et al (2015) demonstrated that individual diet variation usually is highest at intermediate trophic positions and size classes It has remained unexplored how local community structure shapes the relationships between ontogenetic niche shifts and individual diet variation. Due to their relatively low productivity and simple food webs, the subarctic lakes in northern Scandinavia provide an excellent model system to study ontogenetic dietary shifts by top predators as a response to fish community structure (see, e.g., Hortal et al, 2014 for advantages of using lakes as model systems). The study provides novel insights into how community structure shapes individual dietary specialization through species’ ontogeny

| MATERIALS AND METHODS

Findings

| DISCUSSION