Conservation introduction of top predator to an island triggers ecological cascades

• Main Author: Scoleri, VP
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: Rattus rattus
• Online Access: https://eprints.utas.edu.au/35257/; https://eprints.utas.edu.au/35257/1/Scoleri_whole_thesis.pdf

Top predators play important roles in structuring ecosystems and protecting smaller biodiversity by suppressing herbivorous prey and smaller predators. This suppression is achieved through a combination of lethal (e.g. predation, intra-guild killing) and non-lethal (e.g. behavioural, competition) risk effects. Loss of top predators can trigger trophic cascades, which may result in detrimental effects on biodiversity. Reduced predation and competition by top predators can lead to increased abundance of prey and mesopredators, leading in turn to increased herbivory and predation on smaller prey species. Restoration of top predators to ecosystems is a potential tool for conserving biodiversity and controlling the impacts of invasive species. However, long-term manipulative experiments investigating the effects of top predators on ecosystems and their impacts on invasive species are rare.A natural experiment involving the removal of top predators is occurring on the island state of Tasmania, Australia, initiated with the extinction of the Thylacine (Thylacinus cynocephalus) in the 1930s. Tasmania’s current top predator, the Tasmanian devil (Sarcophilus harrisii) has severely declined in the last 25 years due to a novel transmissible cancer, devil facial tumour disease (DFTD). Since it was first detected in 1996, DFTD has spread to most of the devil’s distributional range, causing an overall population decline of 80%, with local declines up to 95%. Field studies suggest there has been an increase in abundance of two invasive species at different trophic levels, the feral cat (Felis catus) and black rat (Rattus rattus) in areas where DFTD has been present for long periods, and this may have caused declines in some small and medium-sized mammal species in long-diseased eastern Tasmania. There is debate, however, as to whether feral cats have responded to devil decline with a change in abundance or behaviour, and the mechanism responsible for these changes in cats and black rats is unclear. There is also evidence of an ...