Among-individual diet variation within a lake trout ecotype: Lack of stability of niche use.

Louise Chavarie,Charles C Krueger,Andrew M Muir,Les N Harris,Michael J Hansen,William M Tonn,Kimberly L Howland,Colin P Gallagher

doi:10.1002/ece3.7158

Abstract

In a polyphenic species, differences in resource use are expected among ecotypes, and homogeneity in resource use is expected within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether specialization of trophic resources by individuals occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within this lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large‐sized individuals and other piscivore individuals. We demonstrated that individual trophic specialization can occur within an ecotype inhabiting a geologically young system (8,000–10,000 yr BP), a lake that sustains high levels of phenotypic diversity of lake trout overall. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes.

Highlights

Phenotypic diversity within fish species that have colonized postglacial lakes often represents early stages of species diversification (Snorrason & Skúlason, 2004)
Our aims were to (a) compare resource use among lake trout individuals within Ecotype 2 by characterizing their fatty acid profiles, (b) determine whether resource-use differences were influenced by life-history traits, (c) characterize and compare morphological variation among groups that expressed different feeding strategies, and (d) determine if genetic differences existed among groups
| 1459 association can be made between body size and niche use (Werner & Gilliam, 1984), we examined a subset of the largest lake trout of this ecotype from our collections (≥900 mm in fork length) referred to locally as “Giants” (Figure 2)

Summary

Introduction

Phenotypic diversity within fish species that have colonized postglacial lakes often represents early stages of species diversification (Snorrason & Skúlason, 2004). Many fishes that have colonized postglacial freshwater systems are assumed to have been plastic generalists (i.e., flexible in use of habitat and food resources) at the time of colonization (Skúlason et al, 2019; Snorrason & Skúlason, 2004). Theory predicts that recently colonized systems with multiple stable and predictable habitats and resources would favor foraging and habitat specialization and increase the probability of eco-morphological diversification (Skúlason et al, 1999; Snorrason & Skúlason, 2004; Van Kleunen & Fischer, 2005)

Objectives

Findings

Discussion

Conclusion