A Comparative study of the Wellington tree weta, hemideina crassidens (blanchard, 1851) in the presence and absence of rodents

Abstract

The impact of rodents (Rattus spp.) on tree weta, Hemideina spp. (Orthoptera: Stenopelmatidae), population density, refuge choice, age structure, sex ratio, and behaviour was investigated on islands with different rodent statuses in the Marlborough Sounds, and on mainland Nelson. A new census technique of counting tree weta in refuges was developed to estimate tree weta densities. Tree weta vulnerable to rodent predation existed in significantly lower densities, and occupied refuges with significantly smaller entrance holes in comparison to tree weta on rodent-free islands. Rodents may reduce tree weta density via a combination of direct predation and interference with reproductive cluster formations. Beyond reduced densities, rodents have had little impact on tree weta age structures. Changes in tree weta population parameters documented on Nukuwaiata Island following kiore (Rattus exulans) eradication showed a significant increase in tree weta density over a one year period. Entrance hole sizes of refuges occupied by tree weta remained constant on Nukuwaiata Island, but refuge height above ground decreased over a one year period. Tree weta collected from habitats with different rodent statuses were observed in captivity to determine differences in behaviour patterns. Tree weta from rodent-infested habitats spent significantly more time inside refuges and significantly less time active in comparison to tree weta from rodent-free habitats. Tree weta are able to coexist with rodents via a good survival of immature weta and modified anti-predator behaviour in adults. The availability of refuges and hence habitat was concluded critical for the long term survival of tree weta with rodents.