The trophic ecology (diet and head morphology) and migration patterns of two closely related salmonid fishes, Arctic char (Salvelinus alpinus (L., 1758)) and Dolly Varden (Salvelinus malma (Walbaum, 1792)), were examined in tributaries of Lake Aleknagik, southwestern Alaska, to test for differentiation between species. Schoener’s index of proportional overlap and multivariate analyses of diets suggested that these species had significantly different trophic niches. Arctic char and the largest individuals of both species had the most diverse diets, and sockeye salmon (Oncorhynchus nerka (Walbaum, 1792)) eggs dominated the diet of both species, especially Arctic char. Arctic char had larger jaws and wider heads than Dolly Varden of similar body length, which may contribute to interspecific diet difference. The species also differed in migration patterns; otolith microchemistry indicated that juvenile Arctic char were produced by nonanadromous mothers, whereas the mothers of the Dolly Varden had been to sea in the season prior to spawning. The species also segregate in spawning habitat (Arctic char in the lakes and Dolly Varden in streams), as well as in juvenile rearing habitat. Our study provides the first evidence of divergent feeding and migratory ecology between sympatric juvenile Arctic char and Dolly Varden, differences that may constrain hybridization and introgression between them.
When Pacific salmon (
Oncorhynchus
spp.) spawn and die, they deliver marine‐derived nutrient subsidies to freshwater and riparian ecosystems. These subsidies can alter the behavior, productivity, and abundance of recipient species and their habitats. Isotopes, such as nitrogen‐15 (
15
N), are often used to trace the destination of marine‐derived nutrients in riparian habitats. However, few studies have tested for correlations between stable isotopes and physiological responses of riparian organisms. We examined whether increases in
δ
15
N in terrestrial insect bodies adjacent to salmon spawning habitat translate to changes in percent nitrogen content and body size. This involved comparisons between distance from a salmon‐bearing river, marine‐derived nutrients in soils and insects, soil moisture content, and body size and nitrogen content in two common beetle families (Coleoptera: Curculionidae, Carabidae). As predicted, δ
15
N in riparian soils attenuated with distance from the river but was unaffected by soil moisture. This gradient was mirrored by δ
15
N in the herbivorous curculionid beetles, whereas carabid beetles, which feed at a higher trophic level and are more mobile, did not show discernable patterns in their δ
15
N content. Additionally, neither distance from the river nor body δ
15
N content was related to beetle body size. We also found that nitrogen‐15 was not correlated with total percent nitrogen in insect bodies, meaning that the presence of spawning salmon did not increase the percent nitrogen content of these insects. We conclude that while salmon‐derived nutrients had entered terrestrial food webs, the presence of δ
15
N alone did not indicate meaningful physiological changes in these insects in terms of percent nitrogen nor body size. While stable isotopes may be useful tracers of marine‐derived nutrients, they cannot necessarily be used as a proxy for physiologically important response variables.
Organismal movement can bring individuals, resources and novel interactions across ecosystem boundaries and into recipient habitats, thereby forming meta-ecosystems. For example, Pacific salmon ecosystems receive large marine-derived nitrogen subsidies during annual spawning events, which can have a wide range of effects on aquatic and terrestrial plant species and communities. In this study, we evaluate the effects of cross-ecosystem nutrient subsidies on terrestrial plant growth and reproduction. We conducted a large-scale field experiment with four treatments: (i) addition of a pink salmon (
Oncorhynchus gorbuscha
) carcass, (ii) addition of the drift seaweed rockweed (
Fucus distichus
), (iii) addition of both salmon + rockweed, and (iv) a control. We examined treatment effects on leaf nitrogen and fitness-associated floral traits in four common estuarine wildflower species. We found elevated leaf ∂
15
N in all plant species and all sampling years in treatments with salmon carcass additions but did not observe any differences in leaf per cent nitrogen. We also observed larger leaf area in two species, a context-dependent increase in floral display area in two species, and a limited increase in plant seed set in response to both salmon carcass treatments. In sum, our study suggests that marine nutrients can affect terrestrial plant growth and reproduction.
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