2D to 3D: Exploring Variation of Niche Dimensionality Across Consumers in a Coastal Arctic Ecosystem and Implications...

Each species occupies a distinct ecological niche, defined by a specific set of environmental conditions and resource requirements necessary for its survival and reproduction. However, climate change is altering species distributions, predator-prey relationships, and resource partitioning between species, with these changes being pronounced in the Arctic. Stable isotope analysis of carbon (δ¹³C) and nitrogen (δ¹⁵N) has been widely used to estimate isotopic niches and quantify niche overlap among species using a two-dimensional approach (2D). However, δ¹³C is not always sufficient to differentiate habitat and resource use among species due to minimal variation between end-members. Incorporating sulfur stable isotopes (δ³⁴S) can enhance resolution in such cases. Using an Arctic coastal food web as a model system, we used a three-dimensional isotopic niche approach (3D: δ¹³C-δ¹⁵N-δ³⁴S) with 664 individuals across 49 species spanning multiple taxonomic groups (invertebrates, fish, seabirds, and marine mammals) that utilize resources from benthic and pelagic habitats. We compared the traditional 2D isotopic niches with a 3D framework using nicheROVER to assess how the addition of a third dimension changes niche size estimates and probability of niche overlap between species. We found that several benthic-associated species, including the common eider (Somateria mollissima) and various benthic invertebrates, tended to show greater changes in isotopic niche size with the addition of δ³⁴S than pelagic-associated species. In addition, niche overlap among benthic-associated taxa generally decreased with the 3D approach, suggesting better resolution of habitat use and resource partitioning. This reflects the greater ecological diversity, foraging specialization, and more complex food web structure characteristic of benthic than pelagic ecosystems. We recommend incorporating δ³⁴S for aquatic studies that involve benthic habitats and emphasize the value of multidimensional approaches to increase the resolution of ecological niche analysis.