Direct evidence implicates feral cat predation as the primary cause of failure of a mammal reintroduction programme

As evidence mounts that the feral Cat (Felis catus) is a significant threat to endemic Australian biodiversity and impedes reintroduction attempts, uncertainty remains about the impact a residual population of cats following control will have on a mammal reintroduction programme. Also, behavioural interactions between cats and their prey continue to be an area of interest. Within the framework of an ecosystem restoration project, we tested the hypotheses that successful reintroductions of some medium‐sized mammals are possible in locations where feral cats are controlled (but not eradicated) in the absence of European Red Fox (Vulpes vulpes), and that hare‐wallabies that dispersed from their release area are more vulnerable to cat predation compared with those that remain at the release site. We used radiotelemetry to monitor the survivorship and dispersal of 16 Rufous Hare‐wallabies (Lagorchestes hirsutus spp.) and 18 Banded Hare‐wallabies (Lagostrophus fasciatus fasciatus) reintroduced to four sites within Shark Bay, Western Australia. Nearly all foxes were removed and feral cats were subject to ongoing control that kept their indices low relative to prerelease levels. All monitored hare‐wallabies were killed by cats within eight and 10 months following release. Significant predation by feral cats was not immediate: most kills occurred in clusters, with periods of several months where no mortalities occurred. Once a hare‐wallaby was killed, however, predation continued until each population was eliminated. Animals remaining near their release site survived longer than those that dispersed. The aetiology of predation events observed offers new insights into patterns of feral cat behaviour and mammal releases. We propose a hypothesis that these intense per capita predation events may reflect a targeted hunting behaviour in individual feral cats. Even where feral cats are controlled, the outcome from consistent predation events will result in reintroduction failures. Managers considering the reintroduction of medium‐sized mammals in the presence of feral cats should, irrespective of concurrent cat control, consider the low probability of success. We advocate alternative approaches to cat‐baiting alone for the recovery of cat‐vulnerable mammals such as hare‐wallabies.     

Biodiversity as both a cause and consequence of resource availability: a study of reciprocal causality in a predator-prey system

1. One of the oldest questions in ecology is how species diversity in any given trophic level is related to the availability of essential resources that limit biomass (e.g. water, nutrients, light or prey). Researchers have tried to understand this relationship by focusing either on how diversity is influenced by the availability of resources, or alternatively, how resource abundance is influenced by species diversity. These contrasting perspectives have led to a seeming paradox '... is species diversity the cause or the consequence of resources that limit community biomass?' 2. Here we present results of an experiment that show it is possible for species diversity and resource density to exhibit reciprocal causal relationships in the same ecological system. Using a guild of ladybeetle predators and their aphid prey, we manipulated the number of predator species in field enclosures to examine how predator diversity impacts prey population size. At the same time, we manipulated the abundance of aphid prey in discrete habitat patches within each enclosure to determine how smaller-scale spatial variation in resource abundance affects the number of co-occurring predator species. 3. We found that the number of ladybeetle species added to enclosures had a significant impact on aphid population dynamics because interference competition among the predators reduced per capita rates of predation and, in turn, the overall efficiency of the predator guild. At the same time, spatial variation in aphid abundance among smaller habitat patches generated variation in the observed richness of ladybeetles because more species occurred in patches where predators aggregated in response to high aphid density. 4. The results of our experiment demonstrate that it is possible for species diversity to simultaneously be a cause and a consequence of resource density in the same ecological system, and they shed light on how this might occur for groups of mobile consumers that exhibit rapid responses to spatial and temporal variation in their prey.     

Effects of recreation areas on avian communities in coastal New South Wales' parks

Summary Information on the impacts of outdoor recreation on wildlife within national parks and reserves can be useful to natural area managers. This study aimed to (i) investigate the density, diversity and species composition of avian communities in recreation areas in bushland settings in comparison to surrounding natural habitats, and (ii) determine the influence of the presence of people on avian assemblages in such recreation areas. Avian density, species richness and community composition were compared between six high‐visitation bushland camping and picnic areas (recreation areas) and surrounding undisturbed habitats to examine the effect of recreation areas on avian assemblages. While total numbers of birds detected was found to be higher in recreation areas, species richness trends indicated that a greater diversity of birds was associated with the surrounding natural habitats, which were found to support a taxonomically different avian assemblage to the recreation areas. Interestingly, species previously shown to distinguish urban avian communities were commonly present and often more abundant in the recreation areas than the surrounding natural habitats. We investigated the effect of the intermittent presence of people (rather than clearing alone) and addressed changes in the diurnal distribution of species, by comparing avian assemblages at 22 picnic areas in the morning, at midday and in the afternoon between days of high and low human visitation. Observations of the availability of anthropogenic food resources and subsequent utilization by avifauna were recorded. Generally, avian assemblages appeared to be independent of the presence of people, although the provision of anthropogenic foods is thought to have the potential to adversely affect individual birds. The findings of this study suggest that even small‐scale habitat clearance to create picnic areas adversely affects the avian assemblage present, with temporal changes in visitation levels of humans in these areas appearing to have had no additional influence unless through indirect impacts from anthropogenic foods.