Natural history and ecology of the New Zealand sheet-web spiders Cambridgea plagiata and C. foliata (Araneae: Desidae)

Abstract

ABSTRACTWe investigate key ecological differences and track population dynamics in two sympatric species of sheet-web spider, Cambridgea plagiata and Cambridgea foliata throughout a single breeding season. We undertook a series of weekly population surveys in plots that included both C. plagiata and C. foliata, recording features of their web ecology and of each species’ population dynamics over a single breeding season. We found significant differences in the distribution, web size and substrate, and predominant diet of C. plagiata and C. foliata with the former feeding predominantly on amphipods, building smaller webs and associating with rock walls, resulting in areas of densely aggregated webs. By contrast, moths were the predominant prey type found in C. foliata webs which were larger and more common in open vegetation, resulting in a more uniform distribution of webs within our plots. Additionally, both species exhibit pre-copulatory guarding consistent with the expectations of a first-male sperm priority pattern, suggesting male competition over virgin females. This is despite a consistent female-biased sex ratio. This research not only provides the first ecological data for C. plagiata and C. foliata but provides important context for sexually selected behaviours performed by males in these species.