How elevation affects ship rat (Rattus rattus) capture patterns, Mt Misery, New Zealand

There is a lack of information about how elevation affects the distribution of ship rats in New Zealand. In this study, ship rats (Rattus rattus) were captured in traps set along a 2 km elevational transect (455–1585 m a.s.l.) in beech (Nothofagaceae) forest and adjacent alpine tussock at Mt Misery, in Nelson Lakes National Park, from 1974 to 1993. A total of 118 rats were captured. In years with beech seed fall, upper range limits corresponded with the red beech forest (Fuscospora fusca) limit (~1030 m a.s.l.), with no rats caught above this line in the silver (Lophozonia menziesii) and mountain (F. cliffortioides) beech forest (1050–1408 m a.s.l.) or alpine zone (1425–1585 m a.s.l.). Binary generalised linear models indicated there is an indirect relationship between ship rat capture and temperature, as beech seed production, as well as decreasing elevation, were important predictors of rat capture. There was some evidence to suggest decreasing winter temperature and increasing annual precipitation also influenced ship rat capture and warrants further investigation. Our analyses provide an important insight into the drivers of ship rat elevational distribution, as well as providing a benchmark for comparing both current and future ship rat elevational distributions. Interrogation of more recent rat monitoring data from a range of beech forest types and sites is needed to test hypotheses around how warming temperatures, as predicted with climate change, will both directly and indirectly effect ship rat distribution.