Survival of adult mountain stone weta Hemideina maori (Orthoptera: Anostostomatidae) along an altitude gradient as determined by markrecapture

The mountain stone weta Hemideina maori, a tree weta, is a cold-adapted New Zealand insect that shows increasing body size with increasing altitude and decreasing temperature. This study modelled the monthly survival probability of adult weta at three sites (high, medium and low altitude) in the Rock and Pillar Range, Otago. Survival was predicted to be lowest at the low elevation site where weta are at the lower limit of their current altitudinal range. A total of 504 adult weta were marked and released at all three sites between November 1999 and May 2002. Mark-recapture analysis showed that survival varied over time, being lowest during the summer months. Survival also differed between the sexes, with females having a higher probability of survival than males, but there was no difference in survival between altitudes. Our findings that body size varied significantly with elevation but that survival was similar between sites, suggest that body size at each altitude might be adapted to the local environment. It would be of interest in a longer term study to model survival of Hemideina maori as a function of variation in average summer temperatures, to test predictions about the effects of climate change on populations of alpine ectothermic animals.