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Stable isotope data have made pivotal contributions to nearly every discipline of the physical and natural sciences. As the generation and application of stable isotope data continues to grow exponentially, so does the need for a unifying data repository to improve accessibility and promote collaborative engagement. This paper provides an overview of the design, development, and implementation of IsoBank (www.isobank.org), a community-driven initiative to create an open-access repository for stable isotope data implemented online in 2021. A central goal of IsoBank is to provide a web-accessible database supporting interdisciplinary stable isotope research and educational opportunities. To achieve this goal, we convened a multi-disciplinary group of over 40 analytical experts, stable isotope researchers, database managers, and web developers to collaboratively design the database. This paper outlines the main features of IsoBank and provides a focused description of the core metadata structure. We present plans for future database and tool development and engagement across the scientific community. These efforts will help facilitate interdisciplinary collaboration among the many users of stable isotopic data while also offering useful data resources and standardization of metadata reporting across eco-geoinformatics landscapes. [ABSTRACT FROM AUTHOR]

Resource polymorphism—whereby ancestral generalist populations give rise to several specialised morphs along a resource gradient—is common where species colonise newly formed ecosystems. This phenomenon is particularly well documented in freshwater fish populations inhabiting postglacial lakes formed at the end of the last ice age. However, knowledge on how such differential exploitation of resources across contrasting habitats might be reflected in the biochemical compositions of diverging populations is still limited, though such patterns might be expected. Here, we aimed to assess how fatty acids (FA)—an important biochemical component of animal tissues—diverged across a polymorphic complex of European whitefish (Coregonus lavaretus) and their closely related monomorphic specialist congener vendace (Coregonus albula) inhabiting a series of six subarctic lakes in northern Fennoscandia. We also explored patterns of FA composition in whitefish's predators and invertebrate prey to assess how divergence in trophic ecology between whitefish morphs would relate to biochemical profiles of their key food web associates. Lastly, we assessed how information on trophic divergence provided by differential FA composition compared to evidence of resource polymorphism retrieved from more classical stomach content and stable isotopic (δ13C, δ15N) information. Examination of stomach contents provided high-resolution information on recently consumed prey, whereas stable isotopes indicated broad-scale patterns of benthic-pelagic resource use differentiation at different trophic levels. Linear discriminant analysis based on FA composition was substantially more successful in identifying whitefish morphs and their congener vendace as distinct groupings when compared to the other two methods. Three major FA (myristic acid, stearic acid, and eicosadienoic acid) proved particularly informative, both in delineating coregonid groups, and identifying patterns of pelagic-benthic feeding throughout the wider food web. Myristic acid (14:0) content and δ13C ratios in muscle tissue were positively correlated across fish taxa, and together provided the clearest segregation of fishes exploiting contrasting pelagic and benthic niches. In general, our findings highlight the potential of FA analysis for identifying resource polymorphism in animal populations where this phenomenon occurs, and suggest that this technique may provide greater resolution than more traditional methods typically used for this purpose. [ABSTRACT FROM AUTHOR]

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1. Determining diet is a key prerequisite for understanding species interactions, food web structure and ecological dynamics. In recent years, there has been considerable development in both the methodology and application of novel and more traditional dietary tracing methods, yet there is no comprehensive synthesis that systematically and quantitatively compares the different approaches. 2. Here we conceptualise diet tracing in ecology, provide recommendations for method selection, and illustrate the advantages of method integration. We summarise empirical evidence on how different methods quantify diet mixtures, by contrasting estimates of dietary proportions from multiple methods applied to the same consumer-resource datasets, or from experimental studies with known diet compositions. 3. Our data synthesis revealed an urgent need for more experiential comparisons among the dietary methods. The comparison of diet quantifications from field observations showed that different techniques aligned well in cases with less than six diet items, but diverged considerably when applied to more complex diet mixtures. 4. Efforts are ongoing to further advance dietary estimation, including how reliably compound specific stable isotope analyses and fatty acid profiles can quantify more prey items than bulk stable isotope analyses. Similarly, DNA analyses, which can depict trophic interactions at a higher resolution than any other method, are generating new ways to better quantify diets and differentiate among life-stages of prey. Such efforts, combined with more empirical testing of each dietary method and establishment of open data repositories for dietary data, promise to greatly advance community and ecosystem ecology. [ABSTRACT FROM AUTHOR]

Arctic charr ( Salvelinus alpinus) is generally considered an inferior piscivore compared to brown trout ( Salmo trutta). However, we demonstrate that a recently described profundal spawning piscivore PP-morph of Arctic charr in a subarctic lake has evolved typical piscivore traits (i.e. large jaws, robust skulls), similar to the co-occurring brown trout but different from the sympatric littoral spawning omnivore LO-morph of Arctic charr. A few large-sized LO-morph, most large-sized PP-morph and trout constitute the piscivore guild, but they differed in prey fish selection. Of the fish-eating deep-water PP-morph, 52% had consumed charr, with a peak during the polar night period (68-80% in November-January). In contrast, the LO-morph and trout were mainly (~90%) inter-specific piscivores eating stickleback. Consequently, the PP-morph was the main charr predator and started to feed on fish at a smaller size and took larger prey relative to their body length than the trout. Stable isotope (δC, δN) ratios reflect the dietary specialisations in the upper-water (LO-morph, trout) and the deep-water (PP-morph) environments, besides the piscivorous behaviour of the PP-morph and trout. The existence of a shallow-water piscivore (trout) may explain the origin of this PP-morph, taking benefit of underutilised resources of small-sized Arctic charr in the deep-water habitat. [ABSTRACT FROM AUTHOR]

Climate change is increasing ambient temperatures in Arctic and subarctic regions, facilitating latitudinal range expansions of freshwater fishes adapted to warmer water temperatures. The relative roles of resource availability and interspecific interactions between resident and invading species in determining the outcomes of such expansions has not been adequately evaluated. Ecological interactions between a cool-water adapted fish, the perch (Perca fluviatilis), and the cold-water adapted European whitefish (Coregonus lavaretus), were studied in both shallow and deep lakes with fish communities dominated by (1) monomorphic whitefish, (2) monomorphic whitefish and perch, and (3) polymorphic whitefish and perch. A combination of stomach content, stable-isotope, and invertebrate prey availability data were used to identify resource use and niche overlap among perch, the trophic generalist large sparsely rakered (LSR) whitefish morph, and the pelagic specialist densely rakered (DR) whitefish morph in 10 subarctic lakes at the contemporary distribution limit of perch in northern Scandinavia. Perch utilized its putative preferred littoral niche in all lakes. LSR whitefish utilized both littoral and pelagic resources in monomorphic whitefish-dominated lakes. When found in sympatry with perch, LSR whitefish exclusively utilized pelagic prey in deep lakes, but displayed niche overlap with perch in shallow littoral lakes. DR whitefish was a specialist zooplanktivore, relegating LSR whitefish from pelagic habitats, leading to an increase in niche overlap between LSR whitefish and perch in deep lakes. Our results highlight how resource availability (lake depth and fish community) governs ecological interactions between native and invading species, leading to different outcomes even at the same latitudes. These findings suggest that lake morphometry and fish community structure data should be included in bioclimate envelope-based models of species distribution shifts following predicted climate change. [ABSTRACT FROM AUTHOR]