When One Matters More: Keystone Niche Individuals Shape Population‐Level Niches in Ectothermic Vertebrates

ABSTRACT Intraspecific variation in resource use plays a fundamental role in shaping population‐level ecological dynamics, yet traditional niche theory often overlooks individual contributions. The recently proposed concept of Keystone Niche Individuals, that is, individuals that disproportionately influence their population's niche width, provides a framework to explore how individuals shape ecological niches. We applied this framework to a dataset of 482 salamanders across 21 populations and seven taxa to assess the prevalence and ecological relevance of Keystone Niche Individuals in ectothermic predators. Using dietary data obtained through stomach flushing, we identified Keystone Niche Individuals as individuals whose presence significantly altered population's niche width beyond expected variation. Keystone individuals were detected in 86% of populations, with both niche‐expanding and niche‐contracting individuals frequently co‐occurring. Linear mixed‐effect models revealed that individual contributions to populations' niche were driven by both broader individual diet breadth and dietary uniqueness, suggesting that Keystone Niche Individuals emerge through a combination of generalist and specialist strategies. These findings support the idea that population‐level niche metrics are emergent properties shaped by few influential individuals, challenging the assumption of equal individual contributions. The consistent occurrence of KNIs across species and habitats suggests that this is a general ecological pattern, that highlights the need to incorporate individual‐level variation into ecological frameworks.