Introduction
Background
Scientific Objectives
Outcomes and Benefits
Researchers and Collaborators
Introduced predators have been responsible for the demise of numerous native vertebrates and culminated in broad scale conservation impacts across Australia. At one level there is general consensus that introduced predators can impact multiple prey species by predation, leading to significant population declines. However, it is also increasingly evident that the impacts that introduced predators place upon individual animals, their populations and ultimately entire ecosystems, is very complex. For example, other than predation, introduced predators can impact native species through a number of additional mechanisms including potentially (1) predation pressure (a sub-lethal cost of predator presence) and (2) competition (again a sub-lethal cost). Furthermore the environment, particularly habitat quality, as dictated by rainfall and fire, is likely to be a significant covariate that superimposes itself into the strength of ecological interactions between introduced predators and native species. As yet the contribution of these additional mechanisms to the dynamics of populations and more importantly for influencing the interactions among native species, which drive ecosystem processes, is poorly understood.
This project seeks to examine two major aspects of the interplay amongst introduced predators and native species. The first is to assess the potential for competitive interactions between introduced predators and a conspicuous native predator the Lace Monitor (Varanus varius). Conceivably, competition for food resources could affect native predators via several mechanisms with the most extreme being an intense reduction in prey availability that reduces or slows demographic vital rates causing declines in local population abundance. Alternatively, less intense effects may be observed if Lace Monitors, like other monitors, exhibit compensatory responses to differences in prey density by exhibiting plasticity in life-history, including a reduction in body size, reducing energetic requirements. Similarly, alternate compensatory responses via shifts in diet may decrease the competition between introduced and native predators. However, as yet there is little known about how introduced predators influence the ecology and demography of native predators.
The second aspect of this project is to measure the unseen physiological costs of introduced predators that are promoted via predation pressure. Ecologically, predation-pressure represents the trade-off between foraging behaviour and anti-predator behaviour. While very common, it is the hidden and thus the often-unmeasured cost that predators exert on their prey. As predation pressure increases, so do the costs, as it creates tension between finding food and avoiding predators. At high levels, prey can become chronically stressed, as their nutritional requirements are increasingly difficult to meet. Chronic stress causes reductions in fecundity and health, and as such can influence the population dynamics of prey. Given that Australian fauna have only a short co-evolutionary history with introduced predators, their ecological naivety could predispose them to the pronounced effects of fox-induced predation pressure and in turn a high susceptibility to chronic stress. This component of project seeks, by measuring the sub-lethal physiological consequences of predation pressure, to (1) quantify a key mechanism by which introduced predators could regulate native predator and prey populations; and (2) assist in evaluating the impact of predator control by measuring at the population- and community-level health indices of native species in fox and fox-suppressed habitat.
Huge investments are put into controlling introduced predators- but our current understanding of the effectiveness of these programs is often limited by the capacity to measure only a few ecosystem impacts of these predators. Furthermore, climate (eg. drought) is often overlooked but an essential component influencing the overall dynamic between introduced predators and their interactions with other species. This project seeks via a large collaborative research effort undertaken within "Southern Ark" a large predator suppression project in East Gippsland (undertaken by the Department of Sustainability see www.dse.vic.gov.au/southernark/), to understand the more complex components of how introduced predators and climate impact native species and regulate ecosystem processes. This project will focus on both ecological and physiological measures to assess the impact of foxes on native species.
Measuring physiological traits to detect disease, injury or congenital problems, is a basic premise of biomedical fields, for inferring the health status of individuals. Until relatively recently, the use of similar techniques in an ecological framework or more importantly for assessing the conservation status of wild animal populations had being ignored. However, because physiological traits affect individuals, and individuals in turn affect populations, they represent powerful markers to rapidly assess the conservation status of animals to a diverse array of contemporary conservation problems. In fact, as indicated by recent reviews the specific use of physiological tools for conservation (i.e. the emerging discipline of "conservation physiology") could contribute greatly to understanding and solving applied conservation problems. In particular, there is a need to develop physiological tools to complement existing ecological and genetic methods for addressing certain conservation problems. Increasingly, with the development of analytical tools many physiological components that underpin the fitness of an individual including reproductive, stress, body condition, and immune parameters, can now be readily measured using minimally invasive or non-invasive techniques.
Given the increasing cost effectiveness of obtaining physiological information from wildlife populations, there is the potential for conservation managers to not only document ecological trends in animals, but to also understand the specific physiological mechanisms underpinning population responses to conservation problems. So far the use of physiological tools has been limited to assessing anthropogenic induced problems such as the effects of habitat fragmentation and toxic chemicals on wildlife populations. This project seeks to test the utility of physiological based conservation tools for understanding other major conservation issues, alongside assisting management agencies in measuring the efficacy of their threat abatement strategies.
This project aims to determine if one of the most pervasive introduced predators, the European Fox, impacts individuals and ultimately populations of a native predator (Lace Monitor) and key prey species (mammals and reptiles-see list below for full species details) via ecological and physiological processes.
Specifically this project has the following aims:
The benefits of this project is that it focuses on groups of animals that are not currently studied and thus provides a broader framework in which to assess the impacts of introduced predators on Victorian ecosystems. It uses alternative physiological measures to measure other potential costs that are currently not measured within the overall Southern Ark project and thus provides greater resolution into the factors that introduced predators can use to influence the ecology and ultimately the population dynamics of native species. Specifically this project will:
Principal zoo researchers involved in this project include Dr Tim Jessop and Dr Graeme Gillespie from Zoos Victoria.
This project sits within the larger umbrella of research being undertaken within the Department of Sustainability and Environments Southern Ark project