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

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.

Patterns and repeatability of multi‐ecotype assemblages of sympatric salmonids

“…Populations of some ecotypes were not consistently more or less variable phenotypically than others. There can be high variability among individuals within an ecotype (Chavarie, Howland, et al, 2021; Skúlason et al, 2019). Repeatable differences in trait variation would have been expected to emerge if certain ecotypes consistently accessed a broader range of resources than others (Svanbäck & Schluter, 2012) or were consistently more sexually dimorphic.…”

“…However, examples are few, and there are many cases of populations that have converged in broad resource use but remain distinct in the traits used to acquire those resources (Losos, 2010; Oke et al, 2017). Furthermore, it is unclear whether similarity across assemblages ever extends to repeatability of within‐ecotype trait variability (Chavarie, Howland, et al, 2021).…”

A systematic review of the trophic ecology of eight ecologically and culturally important fish species in the North American Arctic

“…), and small amounts of other insects (Chavarie et al 2016). The specialized benthic morph feed heavily on ants, as well as bivalves and mysids, but fewer fish compared to other morphs (Chavarie et al 2016(Chavarie et al , 2021. The generalist pelagic morph feed on pelagic forage fishes (presumably Coregonus spp.…”

Atlantic cod individual spatial behaviour and stable isotope associations in a no‐take marine reserve

“…Relatedly, “individual resource specialists”, that have a substantially narrower individual dietary niche than the population's niche, are frequently observed within overall generalist animal populations (Bolnick et al., 2003). In other words, individual foraging tactics where individuals primarily consume a subset of the prey items consumed by the entire population often coexist (Chavarie et al., 2021), potentially without fitness consequences (Woo et al., 2008).…”