Niche partitioning in two coexisting species of Pahoroides (Araneae: Synotaxidae)

Abstract

Spiders in the endemic New Zealand genus Pahoroides (Araneae: Synotaxidae) are all morphologically very similar. Two species, Pahoroides whangarei and Pahoroides confusa, coexist in Pukenui Forest near Whangarei, Northland, living in vegetation close to the ground. We tested the hypothesis that P. whangarei and P. confusa occupy distinct ecological niches defined more by conditions at the microhabitat level than at the macrohabitat level. Twenty random sites within Pukenui Forest, from which a range of macrohabitat and microhabitat variables were collected, were sampled by beating vegetation for Pahoroides spiders. Both species were distributed throughout the forest, and in many cases, were found at the same sites. However, neither the presence nor abundance of one Pahoroides species was associated with that of the other. Whereas macrohabitat variables such as aspect, litter cover and overall plant community composition were not associated with either species, a significant association was found between Pahoroides species and the plant hosts upon which they were collected. Pahoroides whangarei was found mostly on the foliage of crown fern (Blechnum discolor) and kiekie (Freycinetia banksii), whereas P. confusa was most often found in the fallen fronds of ni¯kau (Rhopalostylis sapida). Our findings support the hypothesis that the two Pahoroides species have similar habitat preferences at the macroscale, but not at the microscale. We conclude that host plant species is a dominant factor that enables the species to coexist.