Suchergebnisse

Stochastic scenario trees are a new and popular method by which surveillance systems can be analyzed to demonstrate freedom from pests and disease. For multiple component systems—such as a combination of a serological survey and systematically collected observations—it can be difficult to represent the complete system in a tree because many branches are required to represent complex conditional relationships. Here we show that many of the branches of some scenario trees have identical outcomes and are therefore redundant. We demonstrate how to prune branches and derive compact representations of scenario trees using matrix algebra and Bayesian belief networks. The Bayesian network representation is particularly useful for calculation and exposition. It therefore provides a firm basis for arguing disease freedom in international forums.

We compared the efficacy of two different designs of hair-tube for detecting medium-sized, terrestrial marsupials in a range of forest types in south-east New South Wales. The two designs compared were a large-diameter PVC pipe (large hair-tube) and a tapered hair-funnel. In addition, the relative abundance of forage-diggings of the same marsupials was estimated simultaneously in order to provide an independent assessment of their distribution within the same study area. Only two hair-tubes out of 620 contained hair that could be attributed to the target fauna, both from the long-nosed bandicoot (Perameles nasuta). This was despite the widespread occurrence of forage-diggings at all of the 31 transects that were surveyed. Only two species of mammal, the agile antechinus (Antechinus agilis) and the bush rat (Rattus fuscipes), were detected in sufficient quantity to enable statistical analysis comparing the efficacy of the two hair-tube types. For R. fuscipes the large hair-tube was significantly more effective than the hair-funnel. Conversely, the hair-funnel was significantly more effective in detecting A. agilis than the large hair-tube. Our results suggest that both designs of hair-tube, in their current form, are ineffective for surveying for medium-sized terrestrial marsupials. We see three important issues regarding hair-tube design and implementation that require more attention before this technique can be considered an effective surveying tool: hair-tube morphology, the material used to capture hair, and bait type.