Abstract

Predator-prey interactions are vital to ecosystem functioning but may be disrupted by climate change. We investigated a food-web network involving three owl species over 24 years in a semi-arid ecosystem at Bosque Fray Jorge National Park, Chile. We hypothesized that years of low precipitation cause resource scarcity, prompting dietary niche partitioning by owls via diet specialization or differential diversification. Because climate varies across multiple temporal scales (seasonal variability, medium-scale changes influenced by El Ni & ntilde;o-Southern Oscillation cycles, and long-term shifts associated with climate change), we expected food-web characteristics to exhibit matching multi-scale temporal structure. Using 16 932 owl pellets collected over 229 monthly surveys between 1990 and 2015 and analyzed with an asymmetric eigenvector map framework, we assessed temporal patterns in niche partitioning, diet specialization, trophic niche breadth, and prey richness across time scales to evaluate climatic and biotic drivers. Owl trophic characteristics exhibited significant temporal structure at medium (3.4-9.4 years) and long (15-24 years) timescales, the former aligning with climatic oscillations and the latter with decadal shifts. Consistent with the prediction that resource scarcity promotes diet specialization, decreases in precipitation, small-mammal abundance, and ecosystem productivity led to reduced niche overlap and narrower niche breadth at medium scales. At the larger scales, a major shift after 2003 coincided with declines in both precipitation and temperature. Detected changes were also consistent with niche theory but suggest more complex mechanisms at play at this timescale, since decreases in niche overlap were associated not only with diet specialization but also with increases in overall prey richness, indicating the incorporation of unused prey species. Temperature was the strongest driver of large-scale structure in prey richness, exceeding resource-based variables. Together, our results highlight the complex interplay between climatic factors and resource availability in shaping owl-prey networks, and underscore their fragility under ongoing climate change.