Fig 1.
The brushtail possum was introduced from Australia to New Zealand and is now a major pest.
(Photo: Grant A. Morriss.)
Fig 2.
Sampling locations in the Department of Conservation’s Biodiversity Monitoring and Reporting System.
The 1354 sampling locations are located at the vertices of an 8-km grid superimposed over New Zealand’s public conservation lands.
Fig 3.
Spatial design of invasive mammal monitoring conducted at each sampling location [18].
Brushtail possum trapping occurred along each of the four 200-m trap-lines (AA, DD, MM and PP), and the presence/absence of possum faecal pellets was recorded in each of the 30 quadrats located along the four 150-m ungulate/rabbit/hare pellet transects (A, D, M and P). Birds were monitored at each of the bird monitoring stations, and vegetation was monitored at the central 20 × 20-m vegetation plot.
Fig 4.
Trap set on a brushtail possum trap-line at a sampling location in non-forest habitat.
(Photo: David M. Forsyth.)
Table 1.
Change in the cost of monitoring if brushtail possum trapping is reduced from two nights to one night.
Fig 5.
Effects of reducing sampling effort on estimated brushtail possum occupancy and relative abundance.
(a) Occupancy. (b) Relative abundance (Trap Catch Index). There were 85 sampling locations in forest habitat and 79 sampling locations in non-forest habitat. Vertical bars indicate 95% credible intervals.
Table 2.
Change in the relative abundance of possums (i.e. Trap Catch Index) able to be detected for three levels of power for forest locations for two nights and one night of trapping.
Fig 6.
Effects of reducing sampling effort on estimated brushtail possum relative abundance (Trap Catch Index).
(a) Forest habitat (n = 85 sampling locations). (b) Non-forest habitat (n = 79 sampling locations). Abundances are shown for varying numbers of trap-lines (one to four per sampling location) and trap nights (one or two). Vertical bars indicate 95% credible intervals.
Fig 7.
Effects of reducing sampling effort on the bias of estimated brushtail possum relative abundances (Trap Catch Index).
Biases are shown for varying numbers of trap-lines (one to four per sampling location) and trap nights (one or two) relative to the current sampling effort (four trap-lines set for two nights). Circles and vertical lines indicate the mean and potential range of relative bias in estimates of Trap Catch Index as a result of subsampling from four trap-lines per sampling location.