| 要旨トップ | 目次 | | 日本生態学会第73回全国大会 (2026年3月、京都) 講演要旨 ESJ73 Abstract

一般講演（口頭発表） K01-02 （Oral presentation）

#### Between Birch and Berries: Dietary Niche Partitioning Between Sympatric Alpine Herbivore Birds【E】

*Saria SATO BAJRACHARYA（Nord University）, Rakel BLAALID（Nord University）, Jan Eivind ØSTNES（Nord University）, Elise INGVALDSEN（Nord University）, Oddmund KLEVEN（NINA）, Marie DAVEY（NINA）, Erlend NILSEN（NINA, Nord University）

Species coexistence in harsh alpine environments is often facilitated by niche partitioning, yet the stability of these mechanisms is being challenged by climate change and associated environmental shifts. Understanding how closely related species coexist in such a resource-limited environment requires quantifying the extent of niche differentiation and how overlap varies across seasons. Here, we examined seasonal dietary niche partitioning between two sympatric herbivore birds, willow ptarmigan (Lagopus lagopus) and rock ptarmigan (L. muta) during the winter-spring transition across six years in central Norway. Using fecal DNA metabarcoding (ITS2) from 400 genetically identified samples of ptarmigan, we characterized plant diets and examined interspecific differences in diet composition, seasonal shifts, niche breadth and dietary overlap. Model-based multivariate analysis showed strong evidence for dietary differentiation between species and across seasons, with species-specific seasonal shifts in plant occurrence. During winter, partitioning was mostly quantitative where both species relied on birch (Betula sp.), but rock ptarmigan also heavily utilized crowberry (Empetrum nigrum). In spring, dietary richness and divergence increased, driven by an expansion of niche breadth in willow ptarmigan towards emerging bilberry (Vaccinium myrtillus). In contrast, rock ptarmigan maintained a relatively stable and specialized niche, while increasing use of alpine heaths such as alpine bearberry (Arctous alpina) and alpine azalea (Kalmia procumbens). Based on our results, we demonstrate that fine-scale partitioning of shared resources can structure dietary niches in sympatric alpine herbivores and that seasonal divergence is mainly driven by shifts in the relative use of shared taxa rather than complete turnover in diet composition. These findings suggest that coexistence in a low-productivity alpine system may depend on persistent specialization and seasonal flexibility of both ptarmigan species. We suggest that ongoing changes in alpine vegetation, such as shrub encroachment, may alter resource overlap and reshape niche boundaries, particularly for habitat specialists restricted to high-alpine areas.

日本生態学会