Abstract
Human-mediated dispersal of organisms across the world has resulted in species introductions into many vulnerable ecosystems. Invasive mammalian predators have had detrimental impacts on native island biota, leading to declines and extinctions of many endemic prey species. Humans have transported cats (Felis catus) across the world as mousers on ships and as companion animals. The role cats (especially feral) have played in the decline and extinction of several island species is clear; however, different types of cats classified by their associations with humans has an influence on the public perception of cat impacts on wildlife and acceptance of appropriate management strategies.
I studied the spatial ecology of two different types of cats in two different conservation-sensitive areas (Te Anau Basin and Canterbury/North Otago) in the South Island of New Zealand. I conducted this research to gain an insight into companion cat spatial ecology and feral cat population genetics. Specifically, to investigate individual cat movement patterns and population level movements to discover putative geographic barriers to movement. Additionally, I intended to aid formulation and reinforcement of appropriate and current management strategies with respect to conservation-sensitive areas that support high levels of native biodiversity.
In the Te Anau Basin, the township of Te Anau lies on the edge of Lake Te Anau, directly adjacent to Fiordland National Park. The Kepler Mire conservation area, also situated in the Te Anau Basin, is a nearby wetland that supports a diverse range of fauna. I GPS tracked 32 local companion cats (11F:21M) for a maximum of 10 to 14 days over the austral spring/summer. I recorded a total of 19,157 locations prior to filtering data for erroneous locations. Home range and habitat analysis were performed on a filtered dataset of 13,241 locations using 100% minimum convex polygons (MCP) and Objective-Restricted-Edge Polygons (OREP). Dispersal barriers might be acting to prevent movement of tracked cats into Fiordland National Park, but not the Kepler Mire conservation area. I found males (mean MCP: 22.13 ha, OREP: 1.05 ha) exhibited larger movements (home range and distance travelled from home) than females (mean MCP: 8.83 ha, OREP: 0.45 ha) and rural-living cats (mean MCP: 32.54 ha, OREP 1.33 ha) exhibited larger movements than urban-living cats (mean MCP: 5.90 ha, OREP: 0.46 ha). Cats showed a tendency to preferentially select Built, Cover and Sealed habitat features. Although there was great individual variation in the ranging behaviour, there was no sex or age-related difference observed in the cats’ resource selection.
To infer population movements, I used 10 microsatellite loci and a sex-identification marker, in a multiplex framework, to infer population structure of 157 feral cats in the upper Waitaki Basin (Tasman Valley, Ohau River and Ahuriri Valley) and Macraes Flat. I found some evidence of population connectivity between the sites based on migration rates and low FST values, indicating features in the landscape that act to facilitate dispersal. Bayesian clustering analysis noted the presence of three separate clusters; however, assignment rates were low for the Ohau River, Tasman Valley and Macraes Flat sites. Spatial autocorrelation and Mantel tests indicated rough terrain (i.e. mountain ranges) might limit dispersal. Macraes Flat and Ohau River might function as man-made sinks due to lower relatedness scores. Lower relatedness, genetic differentiation scores, and proximity to human habituation suggested there might be genetic input from nearby stray and companion cat populations. Due to large movements exhibited by feral cats in these areas, reinvasion into trapped areas seems likely; however, the Tasman Valley might be able to be managed as an eradication unit, if movement out of the Ohau River and surrounding area is reduced. Continued genetic monitoring of these sites and sampling of local stray and companion cats might help to identify if there is connectivity between different types of cats (i.e. companion, stray and feral). Additionally, continued genetic monitoring might be able to determine if genetic differentiation increases between each site in response to trapping operations.
Tighter regulations regarding companion cat management might aid New Zealand conservation efforts by reducing and restricting movement and cat interactions with native wildlife. Stricter companion and stray cat regulations might also benefit feral cat control efforts; however, this aspect requires further analysis.