Hair stable isotopes reveal mammalian trophic reorganization between a near-primeval forest and human-modified landscapes

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: Near-primeval forests provide ecological benchmarks for evaluating the functional consequences of landscape transformation. Using stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope analyses of mammalian hair, we compared trophic organization in 26 mammal species between the near-primeval Białowieża Forest and human-modified landscapes in Lithuania and neighboring regions. Based on 2,450 hair samples, we quantified habitat-associated differences in corrected δ 13 C and δ 15 N values, isotopic niche width, niche overlap, and multivariate isotope-space structure. Community-level responses were evaluated using linear mixed-effects models incorporating habitat, trophic guild, collection year, and species identity. Human-modified landscapes were associated with widespread trophic reorganization. Community-level analyses revealed consistent δ 15 N enrichment across trophic guilds, whereas corrected δ 13 C responses were comparatively weak and species-specific. At the species level, δ 15 N values increased in 21 of 26 species, significant habitat-associated separation in isotopic space was detected for most taxa, and isotopic niche contraction was substantially more common than expansion (11 vs. 4 species). The magnitude and direction of isotopic responses varied among species, indicating heterogeneous trophic adjustments to landscape transformation. Our results demonstrate that human-modified landscapes reorganize mammalian trophic structure through changes in nitrogen pathways, resource use, and isotopic niche configuration. These changes occurred despite continued species persistence, indicating that taxonomic composition alone may substantially underestimate forest ecosystem transformation. Stable isotope analysis reveals functional reorganization that remains largely invisible to traditional biodiversity assessments, providing a powerful approach for assessing changes in forest ecosystem functioning and trophic integrity under landscape transformation.

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