Suchergebnisse

The influence of the European rabbit (Oryctolagus cuniculus) on the survival of medium-sized native mammals remains unclear despite 60 years of speculation. Most medium-sized native species that might have been affected by the presence of rabbits are extinct, rare, or endangered. This limits the opportunity to study their interaction with introduced herbivores. We studied the effect of changes in rabbit density on aspects of the ecology of burrowing bettongs (Bettongia lesueur) reintroduced to mainland Australia on Heirisson Prong, Shark Bay, Western Australia. The rabbit population at the site grew to a 10-year high concomitant with a dry summer and low and declining pasture cover. Rabbit browsing led to widespread defoliation of, and subsequent death of, many palatable shrubs. Despite these adverse conditions, reproduction, recruitment and rate of increase of bettongs did not vary with changes in rabbit density, nor did the survival of adult males and females. This work casts doubt on the idea that competition with an introduced herbivore, such as the rabbit, was an important factor in the decline of the burrowing bettong. It highlights the need to understand the ecologies and life histories of native and introduced species in order to manage for the long-term persistence of native species.

The diets of burrowing bettongs and European rabbits were studied on Heirisson
Prong at Shark Bay, Western Australia, over two winters (1996 and 1997) and
two summers (1996/97 and 1997/98). This was during a period when the
rabbit population was increasing to high levels and projected foliage cover
was decreasing, presenting environmental conditions likely to exacerbate
competition. The diets of bettongs and rabbits were significantly different in
both winter and summer. The mean overlap in diets shifted from 43% in
winter to 56% in summer. Bettongs were able to vary their diet in
response to environmental conditions while rabbits perished in large numbers
during the second summer. The winter diet of bettongs included hypogeal fungi
(19–23%), fruit and forbs; their summer diet included seed, stem,
and the foliage of shrubs. Grasses dominated the winter diet of rabbits;
forbs, 'other shrub species', and browse from shrubs were included
also. In summer, rabbits ate mainly roots (30–35%), browse and
stems from shrub species. Bettongs ate food items that rabbits did not, and
were better able to use common resources. The lack of significant dietary
overlap between rabbits and bettongs suggests minimal competition at times of
potentially limited food resources. These results suggest that rabbits alone
are unlikely to have brought about the mainland extinction of bettongs.

Foxes, wild dogs, feral cats, rabbits, feral pigs and feral goats are believed to have deleterious impacts on native biodiversity in Australia. However, although considerable resources have been expended controlling these six species, little is known about national patterns and costs of control and monitoring. We therefore conducted a survey of pest-control operations undertaken by conservation-focused organisations in Australia. A total of 1306 control operations were reported, with most conducted during 1998–2003: there was little information prior to 1990. Foxes and rabbits were the most, and feral cats the least, frequently controlled pest species. The total area on which control was undertaken in 2003, the year for which most information was available, ranged from ~0.4 × 104 km2 for feral cats to ~10.7 × 104 km2 for foxes. A wide range of techniques and intensities were used to control each of the six species. The estimated cost of labour expended on control in 2003 ranged from $0.4 × 106 for feral cats to $5.3 × 106 for foxes. Monitoring of the pest or biodiversity occurred in 50–56% of control actions in which foxes, wild dogs and feral cats were targeted, but only 22–26% of control actions in which rabbits, feral pigs and feral goats were targeted. Our results are discussed in relation to previous studies of pest animal control and monitoring in Australia.