The effects of cluster fencing on native and introduced fauna

The effects of cluster fencing on native and introduced fauna

Apex predators may perform important ecological roles such as the regulation of herbivores and or mesopredators. Removal or loss of apex-predators is thought to cause negative effects for ecosystems, including mesopredator release which may facilitate cascading effects on species at lower trophic levels as predicted by the Trophic Cascade Hypothesis (TCH). Australia has one of the highest mammal extinction rates on Earth and is in a unique situation because the three largest mammalian carnivores are all introduced species. Dingoes (Canis familiaris) are expected by some to suppress foxes (Vulpes vulpes) and feral cats (Felis catus) and indirectly alleviate predation pressure on smaller native fauna, although evidence for these processes remains equivocal. It is therefore critical that the ecological role of dingoes is better understood before potentially unreliable studies are used to inform predator management practices.

I conducted a comprehensive literature review of studies investigating dingo-mesopredator relationships. This review showed that most studies were correlative and therefore had little power to measure the causal roles of dingoes in ecosystems, highlighting the need to undertake better designed experiments. I support the use of stronger-inference studies that manipulate the abundance of dingoes in order to further elucidate the ecological role of dingoes in Australian ecosystems. I therefore undertook a stronger-inference manipulation experiment which removed dingoes from inside two closed (cluster fenced) systems in south-west Queensland where remotely sensed vegetation monitoring, sand plot passive tracking indices (PTI) and spotlight surveys were used to monitor the ecological outcomes of the sustained removal of an apex predator. Following the manipulation, I did not observe a mesopredator release of foxes or cats and I was unable to demonstrate negative relationships between dingoes and these sympatric predators, indicating that the mechanisms underpinning predicted mesopredator releases were absent. My experiments revealed no evidence of lower overall wildlife population abundances within the fences where dingoes were absent and that vegetation trends were almost identical inside and outside the fences. I concluded that although sympatric predators may interact negatively with each other on smaller spatiotemporal scales, these negative interactions did not scale-up to the population level or cause a mesopredator release.

I advocate that future experiments investigating the ecological role of the dingo should transcend the systemic and continued use of low-inference study designs currently being used to investigate the subject. More studies need to incorporate the essential elements of experimental design, especially the use of a measured treatment effect, randomisation and replication of treatments. Studies should also be conducted over longer time intervals (3-5 years), especially when conducted in arid ecosystems, which may also assist in disentangling bottom up and top down effects.

My findings align with other global predator manipulation studies and suggest that the negative effects of trophic cascades are unlikely to occur following the removal of the dingo.

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