Habitat fragmentation is a process that is affecting ecosystems worldwide and is broadly driven by anthropogenic changes. Current research has shown that forests in New Zealand make up just one quarter of the country’s land area and that they have been fragmented into roughly 120,000 separate remnants with an average size of 54 ha. Under the current NZ Department of Conservation biodiversity monitoring program, weta (Hemideina species) are the target indicator species for invertebrates. However, this is problematic because there is limited evidence confirming weta populations as an effective indicator species. This study investigates the potential for weta to be a useful indicator of habitat change by investigating their response to edge presence within a habitat fragment. In 2016 weta population data was collected using artificial shelters from three native bush habitat fragments in the Cass Basin area. Habitat fragments and stream boundaries were mapped using Google Earth. These boundaries, along with the GPS coordinates of each shelter, were input into ArcGIS to determine the distance from shelter to fragment edge or barrier. Weta population per shelter versus distance from fragment edge was plotted. Canopy cover was estimated while performing a walking track of shelter transects.
Results/Conclusions
The three fragments were of varying sizes, 3.41, 3.55, and 13.3 hectares respectively, however they were composed of similar vegetation. We used a linear regression to explore any relationship between weta population per shelter and the distance to a fragment edge. The results revealed a R2 value of 0.25 with a P-value of 7.61x10-6, indicating a pattern of weta being found in higher numbers in the presence of an edge. The results support the hypothesis that weta are affected by habitat fragmentation and the resulting edge effects. We then treated streams as a fragment edge and used a linear regression to investigate if they may act as a natural fragment barrier. The results, a R2 value of 0.054, indicate that weta are affected by human-driven habitat fragmentation but not natural fragment barriers such as stream presence. When investigating canopy cover and weta population, a preference for 30%-40% canopy cover range was found. This removed canopy cover as a source of influencing bias on the fragment edge preference pattern. Overall, our results give support to the NZ Department of Conservation’s and the larger scientific community’s continued use of weta as an indicator species.