Suchergebnisse

Exotic species have had devastating impacts worldwide and are a major threat to native wildlife. Human commensal species (hereafter commensals) are a special class of exotic species that live largely off the resources associated with human activity. The encroachment of commensals from an urban area into surrounding bushland has been frequently overlooked as an important component of urban impacts, even though human-commensals are common to many urban regions globally. In this review, we present theoretical and empirical evidence for the processes and outcomes occurring when exotic commensal species encroach into native bushland. Specifically we ask when, how and why exotic commensal species encroach into bushland, what determines whether they establish, and what are the ecological consequences. We focus on the black rat, Rattus rattus, arguably the archetypal commensal species with a cosmopolitan distribution and the greatest potential for ecological damage of all the commensal rodents. We expect that the processes that we outline apply to other commensal species more broadly. We argue that commensals are in fact natives of the urban milieu and only become alien when they encroach into peri-urban bushland. We propose that the mechanisms of this encroachment will be different from those of other, non-commensal exotic species because urban areas act as dispersal hubs to overcome many of the barriers of invasion that other exotic species face. We suggest that resource supplementation by urban areas creates a great potential for promoting encroachment, invasion as well as impact. However, biotic and abiotic barriers to invasion are still relevant for commensals, highlighting the need to maintain the integrity of ecosystems and wildlife populations in urban edges so as to prevent commensal incursion. We examine how commensal black rats affect wildlife via three fundamental mechanisms, namely, predation, disease transfer and competition for resources, and also consider their possible positive impacts acting as functional replacements for lost natives. We conclude the review with an outline of research priorities and future directions that are essential for progressing our understanding of the ecology of commensal species.

The black rat (Rattus rattus) is among the world's worst invasive species, having spread across the globe in close association with the spread of human settlement. It is the source of some of the worst diseases affecting humans and is thought to have had a devastating impact on native wildlife, especially in island ecosystems. Black rat is likely to have arrived in Australia with the first European settlers, making it among the first of many alien species to invade the continent, and it is now widespread. Yet, its impacts on local wildlife have largely been overlooked. Here, we review the potential for black rat impacts in Australia in terms of its role as a source of disease and threats to wildlife and humans. We first summarise the global evidence for black rat impacts as background to the potential threats it poses and then focus specifically on emerging evidence available for Australian systems. We found a significant gap in our understanding of the ecology of black rats and the ecological role that it plays in Australia. This is despite its role as a source of a diverse range of diseases affecting humans and wildlife and its actions as a predator and competitor of native wildlife in Australia and elsewhere.

Context Bait palatability is a key issue influencing the uptake of toxic baits or non-toxic bait markers. Animals often reject baits with high concentrations of the active compound (whether it is a toxin, vaccine or marker) because of poor palatability, thus reducing the efficacy of baiting. Foraging theory predicts that palatability will be affected not only by the taste of active ingredients in bait but also by an animal's ability to access alternative foods. Yet few studies of bait palatability are measured in the context of an animal's need to search and forage for other food types. Aims The present study examined whether the palatability of Rhodamine B (RB) baits for black rats (Rattus rattus) was affected when foraging constraints were placed on access to alternative food compared with when alternative food was freely accessible. Rhodamine B is a bait marker and was used as a surrogate for other active ingredients likely to be used in pest control management. Methods Each day, RB bait at one of four concentrations was provided to an individual rat along with an alternative food that was either freely available (spatially clumped with foraging constraints absent) or hidden within a matrix of tubes (spatially scattered, thus with foraging constraints present). Key results Black rats exhibited a gradient in how palatable they found RB and preferred baits that contained the lowest concentrations of RB. Importantly, RB baits were more palatable when access to alternative food was made more difficult by applying a foraging constraint. In particular, a 0.2% RB concentration appeared to represent a threshold in palatability where intake at or above this concentration was significantly affected by a rat's ability to freely access alternative foods. The ingestion of RB dye (mg kg–1) was highest in rats that consumed the highest concentrations, even though food intake was reduced. Conclusions The consumption of baits at high RB concentrations was greatly affected by the ease of access to other foods. We suggest the willingness of the animal to consume the bait can be influenced by the effort needed to find alternative foods. Implications A higher incidence of marking in the whiskers or hair of target individuals in the field will only be achieved with the use of the most palatable concentrations of RB and environments providing low alternative food access and abundance. A trade-off between reliable marking and palatability of RB at varying concentrations must be achieved if actual bait uptake in the field is to be more accurately represented. A re-evaluation of palatability experiments may be required as access to alternative foods can have profound impacts on bait uptake.

Context. Potential mammalian prey commonly use the odours of their co-evolved predators to manage their risks of predation. But when the risk comes from an unknown source of predation, odours might not be perceived as dangerous, and anti-predator responses may fail, except possibly if the alien predator is of the same archetype as a native predator.
Aims. In the present study we examined anti-predator behavioural responses of voles from the outer archipelagos of the Baltic Sea, south-western Finland, where they have had no resident mammalian predators in recent history.
Methods. We investigated responses of field voles (Microtus agrestis) to odours of native least weasels (Mustela nivalis) and a recently invading alien predator, the American mink (Mustela vison), in laboratory. We also studied the short-term responses of free-ranging field voles and bank voles (Myodes glareolus) to simulated predation risk by alien mink on small islands in the outer archipelago of the Baltic Sea.
Key results. In the laboratory, voles avoided odour cues of native weasel but not of alien mink. It is possible that the response to mink is a context dependent learned response which could not be induced in the laboratory, whereas the response to weasel is innate. In the field, however, voles reduced activity during their normal peak-activity times at night as a response to simulated alien-mink predation risk. No other shifts in space use or activity in safer microhabitats or denser vegetation were apparent.
Conclusions. Voles appeared to recognise alien minks as predators from their odours in the wild. However, reduction in activity is likely to be only a short-term immediate response to mink presence, which is augmented by longer-term strategies of habitat shift. Because alien mink still strongly suppresses vole dynamics despite these anti-predator responses, we suggest that behavioural naiveté may be the primary factor in the impact of an alien predator on native prey.
Implications. Prey naiveté has long been considered as the root cause of the devastating impacts of alien predators, whereby native prey simply fail to recognise and respond to the novel predation risk. Our results reveal a more complex form of naiveté whereby native prey appeared to recognise alien predators as a threat but their response is ultimately inadequate. Thus, recognition alone is unlikely to afford protection for native prey from alien-predator impacts. Thus, management strategies that, for example, train prey in recognition of novel threats must induce effective responses if they are expected to succeed.

Populations of feral cats, foxes and dingoes were assessed at four sites in
the northern Simpson Desert from May 1995 to October 1996 using track counts.
Counts were based on presence/absence of footprints on sandplots placed
randomly throughout each of the four sites, with all habitats being sampled in
accordance with their availability. Sandplots were repositioned between
sampling periods so that data were temporally independent. This unbiased
method was used to assess the reliability of more conventional indices of
carnivore abundance based on spotlighting and counts of footprints on roads,
which were run concurrently with the random sandplot counts. The sandplot data
were also used to assess habitat use of the three study species.
Counts on regularly spaced sampling plots along roads were correlated with
random sandplot counts for foxes, but not for cats. Conversely, an index of
activity based on counting individual tracks along roads was correlated for
cats, but not for foxes. Spotlighting counts appeared to have little
relationship with random sandplot counts for either species, with random
sandplot counts and spotlight counts of foxes being correlated for only one of
the four sites and no correlations being apparent for cats.
The sandplot data showed that cats used dune crests preferentially over other
habitats, while foxes preferred both dune crests and roads. Dune crests are
probably used as natural runways by both species. Dingoes used roads
preferentially over other habitats. It was concluded that differences in the
use of roads and other runways by the carnivores can potentially lead to
biases in indices collected along roadways. In relation to the random sandplot
counts, foxes were overestimated by road counts and spotlighting relative to
cats, the latter bias being related possibly to temporal differences in the
activity patterns of the two species.

Populations of feral cats, foxes and dingoes were assessed at four sites in
the northern Simpson Desert from May 1995 to October 1996 using track counts.
Counts were based on presence/absence of footprints on sandplots placed
randomly throughout each of the four sites, with all habitats being sampled in
accordance with their availability. Sandplots were repositioned between
sampling periods so that data were temporally independent. This unbiased
method was used to assess the reliability of more conventional indices of
carnivore abundance based on spotlighting and counts of footprints on roads,
which were run concurrently with the random sandplot counts. The sandplot data
were also used to assess habitat use of the three study species.
Counts on regularly spaced sampling plots along roads were correlated with
random sandplot counts for foxes, but not for cats. Conversely, an index of
activity based on counting individual tracks along roads was correlated for
cats, but not for foxes. Spotlighting counts appeared to have little
relationship with random sandplot counts for either species, with random
sandplot counts and spotlight counts of foxes being correlated for only one of
the four sites and no correlations being apparent for cats.
The sandplot data showed that cats used dune crests preferentially over other
habitats, while foxes preferred both dune crests and roads. Dune crests are
probably used as natural runways by both species. Dingoes used roads
preferentially over other habitats. It was concluded that differences in the
use of roads and other runways by the carnivores can potentially lead to
biases in indices collected along roadways. In relation to the random sandplot
counts, foxes were overestimated by road counts and spotlighting relative to
cats, the latter bias being related possibly to temporal differences in the
activity patterns of the two species.

A technique to age wild house mice, Mus domesticus, in Australia using the dry weight of the eye lens based on known-age mice from semi-natural enclosures is described and presented for 3–32-week-old mice. At four sampling periods from November 2000 to September 2001, the age frequency distributions of free-living house mice were determined using this relationship. The distributions of ages shifted between seasons from relatively young animals at the beginning of the breeding season (November 2001), coinciding with low mouse abundance, to progressively older distributions in each sample as breeding continued, ending with the cessation of breeding and a population crash before the last sample. No significant difference was detected between the sexes at any of the four periods. These results are consistent with the suggestion that the formation of mouse outbreaks requires a shift in age structure towards younger mice.

Context Small mammals may traverse the urban fringe and use both natural and anthropogenic resources. In Australia, human commensal black rats (Rattus rattus) and native long-nosed bandicoots (Perameles nasuta) are important tick hosts, which can be found persisting at the urban fringe, leading to human–wildlife conflict. Aims We aimed to (1) determine the relative activity of small mammals in yards and associations with yard attributes, (2) compare activity of black rats and long-nosed bandicoots in bushland with activity in yards and (3) determine the proportion of black rats and long-nosed bandicoots that crossed the urban fringe. We predicted that native bandicoots would be more active in bushland habitats and that black rats would be more active in yards. Methods We used camera trapping in 56 residential yards, 18 of which were paired with adjacent bushland to measure small mammal activity in the two habitats. We recorded yard attributes and examined these associations using generalised linear models. We used isodar analysis to investigate black rat preferences of bushland habitat compared with yards, and we used Rhodamine B baiting to investigate movement at the urban fringe. Key results We found that black rats were the most active small mammal in residential yards and were detected in more yards than other small mammals, followed by bandicoots. Black rat activity was greater in yards adjacent to bushland, but no other yard attributes were associated with black rat and bandicoot activity. Overall, activity tended to be higher in bushland than in yards at paired locations. Conclusions Our findings suggest residential yards likely provide high-quality resources for long-nosed bandicoots. Low rates of movement at the urban fringe (6%), and a preference for bushland at low densities suggests that black rats may be synanthropic rather than commensal, occupying an urban niche but not depending on anthropogenic resources as expected. Implications Residential properties located adjacent to bushland may be exposed to increased black rat activity in yards. Future work should consider how introduced rats may be controlled in bushland to assist urban rat control efforts and avoid non-target impacts. Residential yards are likely to be important habitat for the persistence of long-nosed bandicoots in urban environments.

This study summarises the results of a patchy, low-intensity hazard-reduction burn on the small mammals and lizards of Mumbulla State Forest and Biamanga National Park. About half of the study sites in the patchwork of alternate logging regrowth and unlogged forest had been burnt in April 1999. Prior to burning (winter 1998), there were significantly more Antechinus agilis in those north-west-facing sites that burnt in 1999, than in the south-east sites that burnt. By 15 months post-burning this trend had reversed, with more A. agilis in the burnt south-east sites. In contrast, burning had an initially positive effect on the abundance of Rattus fuscipes, with significantly more in the burnt south-east than burnt north-west sites four months post-burning compared with 1998 (pre-burning). This influence of aspect may be attributable to the fact that fires generally burn more intensely on the drier north-west slopes, removing more of the leaf litter and vegetative cover and making post-fire conditions harsher. Antechinus swainsonii became extremely scarce in the forest after the burning. Twenty months post-burning (summer 2000), there were significantly more Lampropholis delicata in the unburnt sites than in the burnt sites compared with 1999 (10 months post-burn). Lampropholis guichenoti were affected to a much lesser extent and recovered quickly, and Eulamprus heatwolei were generally unaffected by the burning. The hazard-reduction burn came 19 years after a high-intensity bushfire and logging operation in this forest. The results of the two fires were similar for the two Antechinus species and the Eulamprus species but contrasted for the other species. Hazard-reduction burning is widespread and accepted as a management tool and, following the New South Wales bushfires of 1994–95 and 2001–02, will probably increase in use. Our results, however, suggest that the biodiversity impacts of burning are complex and multidirectional, posing a significant challenge to conservation managers.

The quokka, Setonix brachyurus, is a medium-sized, macropodid marsupial that is endemic to south-western Australia. It has declined markedly in its distribution and abundance since the early 1930s and is listed as vulnerable under IUCN criteria. The presence or absence of quokka populations at 66 sites in the northern jarrah forest of Australia was investigated using generalised linear models (GLM). We hypothesised that fox control and the presence of a mosaic of post-fire seral stages within Agonis linearifolia swamp vegetation were important in predicting the presence of quokkas. The number of poison meat baits delivered per hectare, the average number of years since the swamps burnt and the number of post-fire age classes within the swamps (mosaic value) were used as explanatory variables. Two models had substantial support (ΔAICc < 2), with the best approximating model including the variables 'baiting' and 'swamp age', and the second-best model including the additional variable 'swamp mosaic value'. The two best models had Akaike weights (weight of evidence as being the best model of the data) of 0.465 and 0.308 respectively. We used an information-theoretic approach and multimodel inference to determine the best approximating model of baiting, swamp age and swamp mosaic, and Akaike weights to assess model fit and to rank variable importance. Baiting had a model average parameter estimate of 98, swamp age 79 and a mosaic of swamp age classes 42, implying that baiting was more than twice as important as the number of swamp ages classes at a site in predicting the occurrence of quokkas. Evidence from our analysis therefore supports previous studies that concluded that continued fox control and the maintenance of a mosaic of early seral stage (<10 years since fire) and long unburnt habitat (>19 years since fire) are essential for its conservation.

The potential for the quokka (Setonix brachyurus (Quoy & Gaimard, 1830)), a threatened macropodid marsupial, to increase in abundance following the initiation of predator control was investigated by determining the cause of deaths of radio-collared individuals. Predation was identified as a major cause of death followed by road kills. The non-parametric Kaplan–Meier method modified for staggered entry of individuals was used to estimate survivorship. Although males and females were affected differently by each cause of mortality, their overall survivorship did not differ significantly. Individuals alive at the beginning of the 25-month study had a 61% chance of surviving to the end. This represented an 81% chance of surviving for 1 year. There was no significant difference in survivorship between adults and juveniles. Current rates of adult and juvenile survivorship should allow population recovery, although none has been evident. Pouch young mortality is hypothesised to have inhibited the anticipated quokka population increase since the initiation of predator control. The observed expulsion of pouch young by females when threatened may be a primary predator avoidance strategy.

A study was conducted to determine the validity of using transect counts of faecal pellet groups to estimate population densities of a threatened, macropodid marsupial – the quokka (Setonix brachyurus (Quoy & Gaimard, 1830)). Mark–recapture estimates of population density were regressed against counts of faecal pellet groups at six sites with and three sites without fox control within the northern jarrah forest of Western Australia. Significant linear relationships were found between population density and pellet counts for all sites (r2 = 0.56, P < 0.02) and when all unbaited sites were excluded (r2 = 0.98, P < 0.01). We suggest that this method could be used for broad-scale monitoring of this threatened species.

Context
There is growing recognition of the importance of animal personality in wildlife ecology and management. Individuals that differ consistently in their behaviours from others of the same population are considered to exhibit different personalities. Personality can be easily quantified with repeat tests on animals held in captivity. However, captive-based tests may not always be possible for logistical reasons and tests conducted in captivity can alter naturally occurring behaviours. Development of methods to assess personality in the field over short-term capture is an important alternative to long-term captive tests.

Aims
To develop and refine field-based tests that can be used to easily define personality traits of wild common brushtail possum (Trichosurus vulpecula), eliminating the need to bring individuals into captivity for an extended period of time.

Methods
We developed a series of short-term capture protocols to quantify personality traits of the common brushtail possum in the field, using handling-bag tests, modified open-field tests, trap-behaviour tests and release tests.

Key results
Personality traits of brushtail possums could be measured in several different ways, but refining methods was crucial to reveal traits efficiently. Behaviours related to several personality traits (boldness, docility and activity/exploration) could be measured rapidly in the field with our methods, and were repeatable over time.

Conclusions
Rapid, reliable and easy-to-perform quantification of personality of brushtail possums in the field is possible. This may sometimes be the only available option, and has advantages over long captive trials in terms of animal welfare and cost.

Implications
The present study provides a baseline for future research on the personality of common brushtail possums and its application to management and control strategies for the species.