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In 1938, zoologist Ellis Le Geyt Troughton expressed concern that Australia’s unique wildlife was struggling to adapt to the challenges posed by new predators and changing environments.
Today, the impact of introduced species, particularly foxes and feral cats, on Australia’s native fauna has become a well-established issue in conservation discourse. Researchers and conservationists have reached a consensus that these predators have significantly contributed to the decline and extinction of many native mammals.
In response to this crisis, various conservation initiatives and government bodies have undertaken extensive measures aimed at controlling these invasive predators through trapping, shooting, and poisoning programs.
However, a pivotal question looms: Did foxes and cats actually lead to the extinction of species such as the desert bandicoot, lesser bilby, and central hare-wallaby? Recent studies reveal that the evidence supporting this notion may not be as robust as previously believed.
Research Overview
Our research involved cataloging 57 mammal species believed to have declined or gone extinct due to predation from foxes and 80 species linked to cats. We investigated primary sources to identify direct connections between these predators and the declines in native populations. Our inquiry was guided by three fundamental questions.
1. Timing of Extinctions in Relation to Predator Arrival
It is a common assertion that extinctions occurred after foxes and cats were introduced to Australia. To investigate this, we gathered last recorded sightings of extinct species and compared these against timelines and maps showing the arrival of both foxes and cats.
From our analysis, we documented 164 local extinctions affecting 52 species. Notably, approximately 31% of these extinction records did not support the narrative that they closely followed the arrival of predators. In fact, 44% of extinctions attributed to foxes and 20% attributed to cats may have occurred before these predators were introduced.
While it is important to acknowledge the possibility of inaccuracies in record-keeping, our findings suggest that more investigation is warranted before drawing conclusions about the role of foxes and cats in these extinctions. For example, the banded hare-wallaby was last sighted on the mainland 4 to 30 years prior to documented fox arrivals.
Additionally, certain species have demonstrated resilience; the eastern barred bandicoot cohabited with cats on the mainland for over 150 years before its extinction, and both species still inhabit Tasmania together.
2. Existing Evidence of Predation Impact
Our study revealed that experts suggest predation by foxes and cats is responsible for putting 57% of Australia’s threatened mammals at risk. However, for such claims to hold weight, one would expect substantial ecological studies linking these predators to population declines.
We examined 331 studies to assess whether they contained data on predator and prey populations and linked predation to declines in native species. Alarmingly, 76% of the studies on threatened species associated with foxes and 80% with cats lacked supporting population data.
While specialists do not argue that foxes and cats universally threaten all at-risk species, our focused analysis on those deemed most vulnerable yielded similar findings. While foxes and cats are categorized as a “high” threat to mountain pygmy possums, for example, anecdotal evidence fails to substantiate mortality linked to these predators.
In several studies where population data was reported, 50% did not show negative impacts associated with the presence of foxes and cats, indicating a need for a reevaluation of such claims. For instance, while cats are regarded as a “high” threat to long-nosed potoroos, existing population studies do not support this assumption, suggesting these small mammals can coexist with feral cats.
One notable exception is the brush-tailed rabbit rat, where evidence consistently links cat predation to its decline.
3. Correlation Between Predator and Prey Populations
If the introduction of predators is indeed the cause of extinctions, a logical expectation would be the observation that higher predator populations correlate with lower numbers of prey species. Through meta-analysis, we found a negative correlation with fox populations—indicating that increased fox numbers correspond to decreases in threatened mammals, albeit this does not establish direct causation.
Conversely, we found no evidence of a significant correlation with cat populations.
Other Evidence Considerations
Additional support for the notion that foxes and cats impact native species comes from studies suggesting extinct species often fall within a specific weight range that coincides with ideal prey sizes for these predators. However, these findings do not explain why Australian fauna would be particularly at risk. For many years, Australia’s mammals coexisted with native predators, such as dingoes and Tasmanian devils.
While it has been long assumed that Australian mammals are less adapted to surviving against ambush predators, current studies challenge this narrative, demonstrating that Australian rodents can respond to foxes similarly to their counterparts in other regions who evolved alongside these predators.
Some hypotheses even suggest that the ecosystem dynamics in Australia have shifted due to the loss of historical predators, such as the thylacine and marsupial lion, creating an ecological imbalance that may have left native species vulnerable.
Final Thoughts
Our inquiry was not designed to disprove or confirm the belief that introduced predators are primarily responsible for extinctions. Instead, our analysis presents the existing primary evidence regarding these claims, allowing readers to reach their own conclusions.
Widespread assertions regarding the roles of foxes and cats in driving extinctions warrant careful scrutiny. Evidence indicates that the case against them is often based more on expert opinion rather than solid, unequivocal data.
Ultimately, the cause behind the decline of Australia’s mammals remains uncertain. While introduced predators such as foxes and feral cats may play a role, other factors are likely at play, necessitating a broader investigation to uncover the full extent of influences affecting Australia’s native wildlife.
Source
phys.org