Peter B. Banks

Alien predators are more dangerous than native predators to prey populations

Alien predators are widely considered to be more harmful to prey populations than native predators. To evaluate this expectation, we conducted a meta-analysis of the responses of vertebrate prey in 45 replicated and 35 unreplicated field experiments in which the population densities of mammalian and avian predators had been manipulated. Our results showed that predator origin (native versus alien) had a highly significant effect on prey responses, with alien predators having an impact double that of native predators. Also the interaction between location (mainland versus island) and predator origin was significant, revealing the strongest effects with alien predators in mainland areas. Although both these results were mainly influenced by the huge impact of alien predators on the Australian mainland compared with their impact elsewhere, the results demonstrate that introduced predators can impose more intense suppression on remnant populations of native species and hold them further from their predator-free densities than do native predators preying upon coexisting prey.

Predator manipulation experiments: impacts on populations of terrestrial vertebrate prey

Quantifying the relative impacts of top-down vs. bottom-up control of ecosystems remains a controversial issue, with debate often focusing on the perennial question of how predators affect prey densities. To assess predator impacts, we performed a worldwide meta-analysis of field experiments in which the densities of terrestrial vertebrate predators were manipulated and the responses of their terrestrial vertebrate prey were measured. Our results show that predation indeed limits prey populations, as prey densities change substantially after predator manipulations. The main determinant of the result of an experiment was the efficiency of predator manipulation. Positive impacts of predator manipulation appeared to increase with duration of the experiment for non-cyclic prey, while the opposite was true for cyclic prey. In addition, predator manipulation showed a large positive impact on cyclic prey at low prey densities, but had no obvious impact at peak prey densities. As prey population densities general...

Nonlinearity in the predation risk of prey mobility

Odorous waste products such as urine and faeces are unavoidable for most animals and are widely exploited by predators and their prey. Consequently, waste accumulations can be risky and prey which increase their mobility in order to disperse and dilute their waste should avoid a high predation risk until this benefit is balanced by the increasing risks of random predator encounter. This hypothesis was tested for voles (Microtus spp.) in Finland which are vulnerable to predation due to the scent and ultraviolet attractiveness of their urine. The mortality and mobility of radio-collared voles showed a U-shaped relationship, regardless of vole sex, species or population cycle phase. The low risks for prey making intermediate movements suggest that predation risk can exert strong selective pressures on prey such that they have little respite from the risk of being killed.

Mobility decisions and the predation risks of reintroduction

Predation is a common problem limiting the success of efforts to reintroduce vertebrates. Naive animals typically suffer high predation rates soon after release despite strong site fidelity in the first few days that would normally reduce predator encounter rates. However, recent theory predicts that low mobility can be associated with high concentrations of odour wastes that are attractive to predators, leading to low survival for individuals that move little. In this paper we test this model for captive-raised Microtus voles reintroduced into suitable habitat in western Finland where they are mainly hunted by chemo-sensing predators. Patterns in vole movement behaviour showed a humped relationship with time: animals moved little soon after release, then made exploratory movements from 3 to 6 days, which then subsided. Predation rates were highest in the first 3 days, with no vole mortalities occurring after voles began substantially moving beyond their release sites. Moreover, voles that survived the 3-week study period were more mobile than voles that were killed by scent-hunting predators, during the initial 3 days and during the final 3 days when voles also had lower mobility. These results suggest that the innate fear response of naive animals, which limit their movements in an unfamiliar environment, may be counterproductive when reduced mobility leads to waste accumulation that is attractive to potential predators. Consequently, pre-release conditioning of captive-raised individuals may need to consider methods to overcome initial release-site fidelity in order to enhance long-term survival prospects after reintroduction.

Four-legged friend or foe? Dog walking displaces native birds from natural areas

Dog walking is among the worlds most popular recreational activities, attracting millions of people to natural areas each year with diverse benefits to human and canine health. But conservation managers often ban dog walking from natural areas fearing that wildlife will see dogs as potential predators and abandon their natural habitats, resulting in outcry at the restricted access to public land. Arguments are passionate on both sides and debate has remained subjective and unresolved because experimental evidence of the ecological impacts of dog walking has been lacking. Here we show that dog walking in woodland leads to a 35% reduction in bird diversity and 41% reduction in abundance, both in areas where dog walking is common and where dogs are prohibited. These results argue against access by dog walkers to sensitive conservation areas.

Ecological costs of feral predator control : Foxes and rabbits

We used a predator removal experiment to examine the role of red fox (Vulpes vulpes) predation in suppressing rabbit (Oryctolagus cuniculus) population growth in Namadgi National Park in southeastern Australia. At 2 sites, fox abundance was reduced with a 1080 poisoning campaign maintained over 18 months. The responses of rabbit populations in these fox-reduced sites were compared to 2 other sites where fox populations remained intact. In the 2 removal sites, rabbit populations grew to 6.5 and 12.0 times their initial population size within 18 months. In the untreated sites, rabbit populations showed very small population increases over the same period. The experiment demonstrated that 1 introduced pest species suppressed the population growth of another pest species. As fox removal was initially planned to protect native fauna threatened by fox predation, the response of the rabbits represents a serious ecological cost of fox control.

Responses of Australian bush rats, Rattus fuscipes, to the odor of introduced Vulpes vulpes

Predator-avoidance behavior of native bush rats ( Rattus fuscipes ) to an introduced predator ( Vulpes vulpes ) was investigated by measuring their responses to predator odor. Trapping success of wild bush rats was compared between clean traps and traps scented with fox odor, set along creeks in Namadgi National Park in southeastern Australia. Two experimental designs were used; the first measured trapping success of clean and scented traps alternating along a trapline through bush rat habitat in winter, spring and summer. The second design offered a choice of clean and scented traps at each trap station and was repeated in spring and summer. Relative trapping successes were analyzed to determine if rats avoided fox odor. Multiple t- tests showed no avoidance responses with similar numbers of captures in clean and fox-scented traps. Consequences of the apparent naivete of bush rats to the odor of an introduced predator are discussed.

Behavioural, Morphological and Dietary Response of Rabbits to Predation Risk from Foxes

We report on the responses of wild European rabbits (Oryctolagus cuniculus) to a reduction in predation risk from red foxes (Vulpes vulpes) in a predator removal experiment in montane Australia. Specifically we tested whether rabbits in two sites with reduced fox numbers moved further from refuge than rabbits in two sites with abundant foxes. We then compared diet quality by analysing stomach contents, gut morphology and age-specific body mass to determine if release from predation risk enables rabbits to access higher quality food and hence attain higher body mass and condition. During spotlighting on three quarterly surveys in 1994-1995, rabbits in fox removal sites were observed, on average, three times further from refuge compared to rabbits at sites with foxes. However, this freedom to forage far from cover did not translate into a higher quality diet. Analysis of the nitrogen and neutral-detergent fibre content of stomach samples taken from a shot sample of rabbits at their peak densities after fox removal showed no differences in short-term diet quality of male or female rabbits due to fox removal. In contrast, analyses of gut morphologies, which reflect long-term fibre intake, suggested that rabbits in removal sites fed on a diet higher in fibre and hence of lower quality. This was possibly due to the large increases in rabbit density associated with fox removal. Despite this, male rabbits in fox removal sites were heavier for their age, had longer intestines, and heavier stomach and gut contents. We suggest that rabbits in fox removal sites compensated for the lower quality diet by increasing intake which enabled them to maintain higher age-specific body mass but only because predation risk was reduced. This result highlights the untenable link between resource limitation and predation risk.

A review of the evidence for potential impacts of black rats (Rattus rattus) on wildlife and humans in Australia

Abstract. 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.

Predators Are Attracted to the Olfactory Signals of Prey

Background Predator attraction to prey social signals can force prey to trade-off the social imperatives to communicate against the profound effect of predation on their future fitness. These tradeoffs underlie theories on the design and evolution of conspecific signalling systems and have received much attention in visual and acoustic signalling modes. Yet while most territorial mammals communicate using olfactory signals and olfactory hunting is widespread in predators, evidence for the attraction of predators to prey olfactory signals under field conditions is lacking. Methodology/Principal Findings To redress this fundamental issue, we examined the attraction of free-roaming predators to discrete patches of scents collected from groups of two and six adult, male house mice, Mus domesticus, which primarily communicate through olfaction. Olfactorily-hunting predators were rapidly attracted to mouse scent signals, visiting mouse scented locations sooner, and in greater number, than control locations. There were no effects of signal concentration on predator attraction to their preys signals. Conclusions/Significance This implies that communication will be costly if conspecific receivers and eavesdropping predators are simultaneously attracted to a signal. Significantly, our results also suggest that receivers may be at greater risk of predation when communicating than signallers, as receivers must visit risky patches of scent to perform their half of the communication equation, while signallers need not.