Seasonal shifts in feeding patterns: Individual and population realized specialization in a high Arctic fish

Abstract

Species with a broad and flexible diet may be at an advantage in a rapidly changing environment such as in today's Arctic ecosystems. Polar cod (Boreogadus saida), an abundant and ecologically important circumpolar Arctic fish, is often described as a zooplankton generalist feeder, which suggests that it may cope successfully with changes in prey composition. This description is justified based on the relatively broad diet of polar cod across sites and seasons. In this case study, we used polar cod dietary data from fall and winter and from two distinct environments, dominated either by Arctic or Atlantic water masses in Svalbard. Our results point to the importance of time and space when drawing conclusions on dietary plasticity and degree of specialization. Polar cod diet differed significantly between fall and the winter and between Arctic and Atlantic domains. Polar cod from Arctic domains displayed a strong realized population specialization on Themisto libellula in fall, and the larger dietary niche width observed in the winter was the product of realized individual specialization, with increased feeding on fish prey. Overall, we did not observe a generalized feeding behavior. If dietary niche width is to inform conservation management, we argue it must be recognized that populations from a single species may adopt seasonally contrasting degrees of dietary specialization and that these populations may differ in their vulnerability to climate‐induced changes in prey community composition.

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

“…The similarity based on lake trout body size between both lakes suggests analogous variables favoring partial reproductive isolation. Although alternative causes of genetic differentiation may be possible, due to the short time since the onset of divergence, post-zygotic isolation seems unlikely in this system (e.g., prezygotic isolation generally evolves more rapidly Coyne et al, 2004) and we therefore favor assortative mating based on size and location as an explanation for the low-level genetic divergence observed. Nonetheless, putative partial reproductive isolation within an ecotype adds to the complexity of diversification and speciation processes potentially occurring within lake trout in Great Bear Lake (Hendry, 2009;Nosil et al, 2009).…”

“…The among-individual specialization may result, to some degree, from variable use of spatially separated resources and possibly temporally variable resources, both of which could be expected in a large northern lake ( Fig. A4; Costa et al, 2008;Cusa et al, 2019;Quevedo et al, 2009). Ecologically, among-individual resource specialization within an ecotype is another form of diversity (Araújo et al, 2008;Pires et al, 2011).…”

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

“…The among-individual specialization may result, to some degree, from variable use of spatially separated resources and possibly temporally variable resources, both of which could be expected in a large northern lake ( Fig. A4; Costa et al, 2008;Cusa et al, 2019;Quevedo et al, 2009). Ecologically, among-individual resource specialization within an ecotype is another form of diversity (Araújo et al, 2008;Bolnick et al, 2003;Pires et al, 2011).…”

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

“…This broad distribution of trophic variation within a population appears to be the case within Great Bear Lake piscivores. The among‐individual specialization may result, to some degree, from variable use of spatially separated resources and possibly temporally variable resources, both of which could be expected in a large northern lake (Figure ; Costa et al., 2008; Cusa et al., 2019; Quevedo et al., 2009). Lake Trout has the reputation of being a mobile predator that displays flexible foraging behavior by moving across spatially disparate habitats, both within and among populations and seasons (Guzzo et al., 2017; Vander Zanden et al., 2000).…”