LANDSCAPE ECOLOGY OF THE WART-BITER DECTICUS-VERRUCIVORUS IN A PATCHYLANDSCAPE

1. Populations of wart-biter Decticus verrucivorus living on habitat i slands in an intensively exploited agricultural landscape in south-eas tern Norway were studied. Auditory recordings of singing males indicat ed that 27 (39%) of 70 habitat islands contained populations in the fi rst year of the study, while 2 years (one wart-biter generation) later the number was 16 (23%). Dispersing male wart-biters were also observ ed, and the dispersal distances measured. 2. Predictors of island occu pancy were identified by applying logistic regression models to the pa ttern of presence/absence, probing the predictive power of both landsc ape variables (island size and isolation) as well as various microhabi tat quality variables (vegetation, aspect and slope). The isolation of habitat islands relative to surrounding wart-biter populations was me asured by two types of connectivity indices: one based on the empirica l probability distribution of dispersal distances, the other on the ne gative-exponential dispersal function. 3. Habitat area and the connect ivity indices were by far the best predictors of occupancy. The probab ility of occupation increased with increasing area and decreasing isol ation. Of the unoccupied habitat islands, the ones with observations o f single males were less isolated than the ones without. From the patt ern of occupancy, the average dispersal distance was estimated to be 4 0 m, while the observed average dispersal distance of males was 37 m. 4. In addition to the effects of area and connectivity, the probabilit y of occupation was positively influenced by increasing slope to the s outh, increasing amounts of the plant Achillea millefolium, and decrea sing fraction of vegetation lower than 10 cm. The probability of local population extinction increased with declining habitat area and incre asing fraction of low vegetation. 5. The situation of the wart-biter i n this highly fragmented study area seems to largely fit a metapopulat ion model: extinctions and absence of wart-biters were adequately pred icted by habitat island size and isolation, and observed dispersal dis tances closely matched estimated dispersal distances from the model.