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Jervis Bay, Australia

Dexter N.,Booderee National Park | Ramsey D.S.L.,Arthur Rylah Institute for Environmental Research | MacGregor C.,Australian National University | Lindenmayer D.,Australian National University
Ecosystems | Year: 2012

At Booderee National Park, south-eastern Australia, the intensive control of the introduced red fox (Vulpes vulpes) resulted in a major increase in the abundance of a browsing macropod, the swamp wallaby (Wallabia bicolor). This has led to a major decrease in the abundance and biomass of a range of palatable plant species. Fox control has also started a trophic cascade that has resulted in a decline in the abundance of the greater glider (Petauroides volans) a folivorous arboreal marsupial, mediated either through increased predation by owls or increased competition with common brushtail possums (Trichosurus vulpecula). We identified five potential scenarios for managing the effects of over-abundant swamp wallabies on the ecosystem as a whole. These were (1) the present scenario of continued intensive fox control and four possible scenarios to redress the problem: (2) ceasing fox control; (3) intensive fox control and intensive wallaby control; (4) introducing dingoes and ceasing fox control; and (5) introducing dingoes and maintaining fox control. We used an ecosystem modelling approach based on a fuzzy cognitive map (FCM) to predict relative estimates of abundance for each scenario for a wide range of taxa in the Booderee National Park ecosystem likely to be affected by each scenario. We addressed uncertainty in our knowledge of the interactions between species by creating alternative models of the system by removing one or more of the uncertain links between species and varying the strength of the remaining interactions in the FCM and aggregated predictions from 100,000 models to estimate the effect of uncertainty on the predictions from our FCM model. In comparison with the current scenario of intensive fox control, scenario 3 had the greatest likelihood of improving the status of palatable plants. Scenarios 2 and 4 reduced the abundance of a range of medium-sized mammals but improved the status of greater gliders, whereas the predicted effects of scenario 5 were uncertain. The FCM modelling approach developed here provided a valuable tool for managers to learn about the potential ecosystem wide effects of management actions while incorporating the likely effects of uncertain knowledge on system outcomes. © 2012 Springer Science+Business Media, LLC. Source

Stutz R.S.,University of Sydney | Banks P.B.,University of Sydney | Dexter N.,Booderee National Park | Mcarthur C.,University of Sydney
Oikos | Year: 2015

Herbivores can dramatically diminish revegetation success, but associational refuge theory predicts that neighbouring plants could hinder browsing of planted seedlings. The key to strategic restoration using associational refuge is to define which patch variables are effective against the appropriate herbivores, at multiple scales, and to understand which stages of the foraging process these variables disrupt. Our study aimed to test the capacity of existing vegetation to act as associational refuge for planted seedlings by affecting search, detection and consumption decisions, and more generally influence herbivore foraging patterns. We conducted a field trial with free-ranging, mammalian herbivores and nursery-raised, native tree seedlings. We quantified seedling browsing damage over time in relation to a suite of existing patch variables at two spatial scales (100 m2 and 4 m2). After two months, 78% of seedlings were browsed, suffering mean foliage loss of 90.5%. Focal seedlings were almost exclusively consumed by swamp wallabies Wallabia bicolor, an abundant generalist browser. Once a swamp wallaby investigated a seedling, the probability of consumption was high (86%). At the large scale, browsing of seedlings was delayed in patches with lower canopy cover and fewer browsed plant species. Seedlings in fern-dominated patches escaped browsing for longer than those in grass-dominated patches. At the small scale, browsing was delayed with higher cover of understorey vegetation. Associational refuge was provided by vegetation with characteristics, and at spatial scales, consistent with disrupted search and detection of focal seedlings by herbivores. Thus strategic placement of seedlings in existing vegetation - based on understanding which herbivore species is responsible and how it responds to vegetation - can take advantage of associational refuge during restoration. However, given rapid seedling detection by herbivores, associational refuge may be inadequate in the long-term under high browsing pressure unless high absolute numbers of seedlings are planted among refuge. © 2014 The Authors. Source

Dexter N.,Booderee National Park | Mcleod S.R.,Australian Department of Primary Industries and Fisheries
Ecology and Evolution | Year: 2015

Ecological traps are habitat sinks that are preferred by dispersing animals but have higher mortality or reduced fecundity compared to source habitats. Theory suggests that if mortality rates are sufficiently high, then ecological traps can result in extinction. An ecological trap may be created when pest animals are controlled in one area, but not in another area of equal habitat quality, and when there is density-dependent immigration from the high-density uncontrolled area to the low-density controlled area. We used a logistic population model to explore how varying the proportion of habitat controlled, control mortality rate, and strength of density-dependent immigration for feral pigs could affect the long-term population abundance and time to extinction. Increasing control mortality, the proportion of habitat controlled and the strength of density-dependent immigration decreased abundance both within and outside the area controlled. At higher levels of these parameters, extinction was achieved for feral pigs. We extended the analysis with a more complex stochastic, interactive model of feral pig dynamics in the Australian rangelands to examine how the same variables as the logistic model affected long-term abundance in the controlled and uncontrolled area and time to extinction. Compared to the logistic model of feral pig dynamics, the stochastic interactive model predicted lower abundances and extinction at lower control mortalities and proportions of habitat controlled. To improve the realism of the stochastic interactive model, we substituted fixed mortality rates with a density-dependent control mortality function, empirically derived from helicopter shooting exercises in Australia. Compared to the stochastic interactive model with fixed mortality rates, the model with the density-dependent control mortality function did not predict as substantial decline in abundance in controlled or uncontrolled areas or extinction for any combination of variables. These models demonstrate that pest eradication is theoretically possible without the pest being controlled throughout its range because of density-dependent immigration into the area controlled. The stronger the density-dependent immigration, the better the overall control in controlled and uncontrolled habitat combined. However, the stronger the density-dependent immigration, the poorer the control in the area controlled. For feral pigs, incorporating environmental stochasticity improves the prospects for eradication, but adding a realistic density-dependent control function eliminates these prospects. © 2015 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. Source

Stutz R.S.,University of Sydney | Banks P.B.,University of Sydney | Dexter N.,Booderee National Park | McArthur C.,University of Sydney
Acta Oecologica | Year: 2015

Herbivore foraging decisions leading to consumption of a plant are complex and multi-faceted, shaped both by the plant itself and by its neighbours. Associational plant refuge arises when neighbours reduce focal plant susceptibility to herbivory. The specific foraging behaviours generating refuge patterns have rarely been examined in free-ranging systems, yet these are key to understanding why such refuge works or fails. We aimed to integrate herbivore foraging and associational plant refuge theories by linking foraging decisions directly to browsing outcomes on focal plants and their neighbours. We tested whether obstructive, unpalatable neighbours reduce the number of patch visits and/or interrupt searching, leading to associational refuge of focal plants. We compared visits by and behaviours of free-ranging mammalian browsers, swamp wallabies (Wallabia bicolor), in control and manipulated plant patches using cameras. Patches (7 m2) comprised a central focal plant (palatable native tree seedling, Eucalyptus pilularis) with neighbours of either existing or manipulated vegetation (unpalatable native daisy, Coronidium elatum). Wallabies made fewer visits to control than manipulated patches, but always browsed the focal plant during the first visit to a control patch. In contrast, wallabies often visited manipulated patches multiple times before browsing the focal plant. These 'futile' visits were both shorter and involved less searching time than visits when the focal plant was browsed. Focal plants escaped browsing for longer in manipulated than in control patches, and although none had escaped browsing after one year, survival was significantly greater in manipulated patches. We demonstrate that reduced investment in searching during visits to manipulated patches drove the associational plant refuge, but this refuge was eventually surmountable. Understanding the behaviours underpinning refuges allows better prediction of outcomes, and explains why refuge can collapse. By shaping foraging behaviour in patches, neighbouring vegetation can increase the probability that palatable plants persist despite high herbivore pressure. © 2015 Elsevier Masson SAS. Source

MacGregor C.I.,Australian National University | Wood J.T.,Australian National University | Dexter N.,Booderee National Park | Lindenmayer D.B.,Australian National University
Australian Mammalogy | Year: 2013

Understanding how animals use available habitat and how disturbance events such as fire influence habitat use is crucial to wildlife management. Relationships between home-range size of long-nosed bandicoots (Perameles nasuta) and vegetation type and fire effects on food availability and vegetation cover were explored. Home ranges and movement of P. nasuta were mapped in burnt and unburnt vegetation using radio-tracking. Compositional analysis was used to study their habitat associations. In 2004, six months after wildfire, no significant relationships were found between home-range size and vegetation type. In 2005, there was a preference for dry and wet forest over heath and disturbed areas. In both years, in ranges that contained both burnt and unburnt vegetation, there was a preference for unburnt vegetation. Home-range size was positively related to the bodyweight of individuals. Fire did not significantly alter home-range size, but did influence the way animals used their home range. Dense understorey might provide vital shelter from predators, and may be particularly important after fire. Wildfire and prescribed burning are major forms of disturbance in many natural areas and this study suggests the importance to P. nasuta of retaining unburnt patches when conducting hazard-reduction burning. © 2013 Australian Mammal Society. Source

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