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Open research questions in Isotope Analysis in Ecology

107 gap statements mined from Isotope Analysis in Ecology papers in our 4.5M-paper local library, which holds 642 papers on the topic — drawn mostly from each paper's own stated research gap, future-work, challenge and limitation notes, and its abstract. The ones listed below are a selection still marked open; each names the study that raised it, with a DOI link where the paper has one.

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What the literature leaves open

  • Our N isotopic measurements of corals and other organisms and N pools across the Bermuda platform confirm a previously identified d15N increase toward the Bermuda coast and make use of that gradient to gain insights into the N sources of corals and the signals recorded by CS-d15N. The d15N of bulk coral tissue is consistent with corals feeding dominantly on some combination of zooplankton-sized organic matter and smaller PN. Depending on the relative importance of these two sources, the trophic d15N elevation of the corals is between 0 and 0.5-1.5‰. This range of values is well below the typical trophic d15N elevation of a heterotroph (of ~3-4‰; Post, 2002), consistent with the recycling and retention of low-d15N metabolic N by symbiont-bearing corals. Comparison of the coral data with d15N data from benthic macroalgae argues against corals’ significant reliance on the DIN. We consider these data as strong support for the dominance of coral feeding over DIN assimilation in this and other nutrient-poor reef settings, despite recent arguments to the contrary (Wiedenmann et al., 2023). In our view, these results conform with the adaptive benefits of the coral-zooxanthellae symbiosis. The coral host is a benthic animal typically occurring in sunlit and nutrient-depleted low latitude surface waters in which phytoplankton growth is limited by the “major” nutrients, nitrogen and phosphorus. Its feeding and metabolism naturally concentrate these nutrients within their tissues, as is true for all heterotrophic organisms, in which the net reaction is respiration. Mutual benefit can be found in harboring algal symbionts that use this concentrated stream of metabolically produced nutrients to fuel photosynthetic growth, with a portion of the resulting organic matter returning to the coral host. Thus, from the perspective of the coral host, their feeding provides chemical energy more than once, as the metabolic production of inorganic nutrients fuels symbiont growth. In contrast, dissolved inorganic nutrient uptake in nutrient-poor tropical and subtropical waters is challenging for phytoplankton, and it should be even more challenging for corals, in which the symbiont requiring these nutrients is isolated by multiple membranes, their own and their hosts, from the external nutrients. There are nutrient-rich surface waters over some coral reefs (e.g., those in the eastern equatorial Pacific as well as in human-impacted coastal regions), where DIN acquisition would be easier, and corals might assimilate DIN under these conditions. However, these environments are also often highly productive and characterized by relatively higher POM and zooplankton concentrations. Consequently, corals inhabiting these environments would have access to abundant organic nitrogen through feeding. In any case, we find the morphological and

    Nitrogen isotope ratios across the Bermuda coral reef: implications for coral nitrogen sources and the coral-bound nitrogen isotope proxy · 2025 · DOI

  • Overall, this study suggests that DDSM habitats have the potential to support certain collembolan species, and soil biodiversity within these habitats warrants attention, especially after stringent reclamation activities have been implemented.

    Variations of collembolan communities in drained and diked salt marsh and adjacent farmland in coastal southeastern China · 2025 · DOI

  • Future studies could consider the existing spatial distribution of bivalve farms and natural habitats across the entire Puget Sound seascape, and the benefits they provide, compared to those envisioned under an expansion of aquaculture activities when estimating the entirety of ecosystem services provided at spatial scales larger than single farms.

    Stable isotopes reveal intertidal fish and crabs use bivalve farms as foraging habitat in Puget Sound, Washington · 2024 · DOI

  • To monitor the biochemical and ecological impacts of environmental problems, future studies should explore the effects of acidification, CO2 levels, and eutrophication on the stable isotope values of AAs in a key macrophyte species and their associated consumers across geographic scales.

    Essential amino acid carbon isotope ratios as indicators of marine macrophyte response to environmental variation · 2024 · DOI

  • Urbanization, biodiversity, and conservation: The impacts of urbanization on native species are poorly studied, but educating a highly urbanized human population about these impacts can greatly improve species conservation in all ecosystems.

    Between forest and city: stable isotope evidence for anthropogenic impacts on the dietary ecology of the vulnerable Wied’s marmosets in Brazil · 2026 · DOI

  • swinhonis would consume more pre- ferred resources when food resources are abundant and compete aggressively for preferred resources when food resources are scarce.

    Formation of Adaptive Trophic Niches of Euryphagous Fish Species in Response to Off-Seasonal Water Level Regulation in Hongze Lake · 2024 · DOI

  • Newly constructed regulation reservoirs experience dramatic seasonal environmental shifts, yet the temporal dynamics of their aquatic food webs remain poorly understood.

    Seasonal Plasticity of Trophic Niches and Food Web Architecture in a Newly Constructed Regulation Reservoir · 2026 · DOI

  • However, studies evaluating foraging habits, resource partitioning, and niche overlap are still scarce.

    Diet and resource partitioning between egrets and herons in an estuarine colony in southern Brazil · 2026 · DOI

  • This study provides the first CSIA-AA evidence of trophic differentiation among oceanic squid paralarvae, addressing a critical gap in understanding early life-phase ecology of cephalopods.

    Trophic ecology of cephalopod paralarvae in the Sargasso Sea revealed from compound-specific stable isotope analysis of amino acids (δ13C and δ15N) · 2026 · DOI

  • However, the relationship between mixotroph metabolic strategy and predation risk remains unclear.

    Effects of mixotrophic metabolism on predation risk · 2026 · DOI

  • Despite extensive dietary studies of the subantarctic fur seal Arctocephalus tropicalis at subantarctic localities, little is known about the diet of colonies inhabiting subtropical regions.

    Diet and isotopic ecology of subantarctic fur seal at the subtropical Amsterdam Island · 2026 · DOI

  • Despite growing evidence of community restructuring, few studies have jointly examined how multiple trophic levels respond to climate forcing within a functional and network-based framework.

    Fish and Zooplankton Co‐Responses to Environmental Gradients Under Different Climate Change Scenarios · 2026 · DOI

  • Climate change is reshaping freshwater ecosystems worldwide, yet the extent to which its effects differ across trophic levels remains poorly understood.

    Fish and Zooplankton Co‐Responses to Environmental Gradients Under Different Climate Change Scenarios · 2026 · DOI

  • However, the slow progress in identifying spatial and temporal patterns and drivers of riverine C has been largely driven by limited data availability.

    OzRiCa: an Australian riverine carbon database of concentrations, gas fluxes and isotopes · 2026 · DOI

  • We also highlight patterns in temporal data coverage, with half of the sites limited to a single measurement.

    OzRiCa: an Australian riverine carbon database of concentrations, gas fluxes and isotopes · 2026 · DOI

  • However, their effects on soil-dwelling communities remain insufficiently explored.

    Positive effects of market garden microfarms on soil-dwelling arthropod diversity: Pilot results from northern Italy · 2026 · DOI

  • Radiocarbon ( 14 C) transfer in terrestrial ecosystems remains poorly understood, particularly for soil fauna under conditions where soil organic matter- and litter-derived carbon pools may contribute differently to animal assimilation.

    Transfer of 14C from peat and plant litter to different ecological groups of earthworms and associated biological responses under controlled conditions · 2026 · DOI

  • Traditional authentication methods relying on supply chain traceability and geographical indications are insufficient to curb rampant fraud, posing economic and health risks.

    Geochemical fingerprinting and machine learning for authenticating sparkling wine origins · 2026 · DOI

  • To date, tobacco research has been largely restricted to geographical differences, while the influences of inter-year and cultivar differences have not been systematically investigated.

    Optimization of geographical traceability models for tobacco: an investigation into the effects of region, harvest year, and variety on stable isotope and multi-elemental profiling · 2026 · DOI

  • However, the long-term impacts of forest restoration involving primary and secondary succession on the recovery of belowground food web energy fluxes and functions remain poorly understood.

    Multitrophic energy flux in soil micro-food webs: the primacy of functional diversity across primary and secondary forest succession · 2026 · DOI

  • Natural isotope ratios (δ 13 C, δ 15 N, and δ 34 S) are effective indicators of soil element cycling, yet the role of phosphorus (P) in regulating their variation under long-term fertilization remains unclear.

    Soil δ13C, δ15N and δ34S values are shaped by nutrient interactions rather than phosphorus alone in an 82-year fertilized grassland · 2026 · DOI

  • Climate change is rapidly altering mountain vegetation zones, yet its impacts on the trophic niche structure and resource use of soil food webs remain poorly understood.

    Elevational gradients shape trophic niche patterns of soil microarthropods on Changbai Mountain, China: Evidence from stable isotope analysis (15N, 13C) · 2026 · DOI

  • However, the influence of feather substructure and contaminant properties on HOP accumulation, and the ability of feathers to reflect regional and interspecific variation in contamination, remain incompletely understood.

    Spatio-species variation of halogenated organic pollutants reflected by bird feathers · 2026 · DOI

  • However, research linking fragment size to nitrogen availability and plant physiological responses in Cerrado remains scarce.

    Variation in δ15N enrichment in Cerrado fragments: edge effects and morphophysiology of Bauhinia holophylla · 2026 · DOI

  • However, monitoring efforts on 6PPD-Q have been focused on water, particulate matter, soils, and sediments, while that in tissues remains scarce.

    Analysis of 6PPD-Q in finfish, shellfish, and marine mammal tissues · 2025 · DOI

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107 gap statements have been mined from Isotope Analysis in Ecology papers in our 4.5M-paper local library, which holds 642 papers on the topic; the gaps come from whichever of those papers state one. They are mostly the research gaps the authors state and the papers' abstracts, plus future-work, limitations and challenges passages. The ones listed below are a selection still marked open; each names the study that raised it, with a DOI link where the paper has one, so you can read the original claim in context.

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