Time-lapse cameras improve our understanding of invertebrate activity in the alpine zone

Abstract

: Understanding when a species is active in its’ environment is essential when designing inventory and monitoring protocols, especially for ectotherms whose activity depends on local weather conditions. The New Zealand alpine zone hosts a diverse native assemblage of invertebrates that are poorly understood yet likely to face an increasing number of threats, particularly associated with climate change and the range expansion of introduced pests. Large-bodied flightless invertebrates are particularily vulnerable to introduced predators, like mice and stoats, which have decimated native species at lower elevations. Using trail cameras, we aimed to understand what conditions and times of the summer field season (spring–autumn) are optimal for monitoring large-bodied alpine invertebrates in the Homer and Gertrude valleys, Fiordland, New Zealand, from late austral spring to late autumn (2020/2021). Beetles (Coleoptera), wētā (Orthoptera), and spiders (Araneae) were the three most common taxonomic groups detected at our sites. The activity of all three groups was significantly influenced by mean hourly temperature. Ninety-five per cent of beetle observations occurred when temperatures ranged from 5.9–12.6°C, while 95% of wētā observations occurred when temperatures were between 6.0–12.6°C. Spiders were active across a broader range of temperatures, with 95% of observations occurring when ground temperatures were between 5.4–13.0°C. The activity of all three groups was also influenced by the time of year. Beetles were observed more often in late spring, wētā in early summer, and spiders in mid-summer. The activity of spiders and beetles, but not wētā, was negatively correlated with precipitation. These results suggest optimal monitoring periods for wētā, beetles, and spiders differ. Still, if the objective is to monitor a range of invertebrates simultaneously, we recommend that surveys occur in spring and mid-summer during nights when temperatures are higher than 5.4°C with little to no rain.