Resource waves across snowpacks and alpine vegetation extend seasonal resource availability in alpine ecosystems

Alpine ecosystems are energy-limited and highly seasonal. Consumers in the alpine zone must track rapidly shifting windows of prey availability during the short growing season. Prolonged snowmelt creates a mosaic of persistent snowfields, scrubs and alpine tundra. In addition to vegetation-dwelling arthropods, wind-transported arthropods deposited on snowpacks, known as arthropod fallout, provide an allochthonous subsidy from lower elevations to alpine environments. Asynchronous arthropod phenology across alpine vegetation and snowpack may create resource waves and prolong food availability for alpine consumers. However, no multi-mountain studies have jointly quantified the phenology of vegetation-dwelling arthropods and arthropod fallout. We examined whether phenological asynchrony between arthropod fallout on snowpacks and vegetation-dwelling arthropods creates sequential resource peaks that extend food availability for alpine consumers. Across three mountains in the Japanese Alps (Tateyama, Norikura and Kisokoma) along broad climatic gradients, we sampled arthropods over 2 years at half-monthly intervals from late May to early August on alpine snowpacks and in alpine vegetation, including Japanese stone pine scrub and alpine tundra. Seasonal changes in arthropod biomass were estimated using taxon-specific length-mass regressions. Community structures of arthropods were analysed using non-metric multidimensional scaling (NMDS). Seasonal changes in abundance and biomass of arthropods on vegetation and snowpacks were examined using generalised linear mixed-effects models (GLMMs). Aphids dominated on snowpacks, whereas Diptera were most abundant in vegetation. Arthropod abundance peaked sequentially across habitats, occurring early on snowpacks, mid-season in Japanese stone pine scrub and late in alpine tundra. Biomass was high early on snowpacks but increased later in vegetation, with the increase occurring earlier in scrub than in alpine tundra. Our findings suggest that arthropod fallout and vegetation-dwelling arthropods provide food resources for alpine consumers during different periods of the growing season. These sequential peaks in arthropod abundance and biomass create resource waves that extend seasonal food availability for consumers. Warming and earlier snowmelt may disrupt these resource waves through taxon-specific responses to changing temperature and snow conditions. Conserving the snow-scrub-tundra mosaic and its temporal complementarity should therefore be a priority for sustaining alpine biodiversity under rapid climate change.