Habitat loss and fragmentation
Western ringtail possums need a very specific habitat to survive which can only be found in the South West of Western Australia. Even though Australia has large protected areas such as National Parks, specific habitats and ecoregions that are most in need of protection are not only underrepresented but are lost at a staggering pace.
If we are serious about habitat protection, we need large, well-connected areas in regions with high quality habitat instead of in places that are not of any other use to us. Strict clearing legislation needs to protect them in perpetuity from threats like urbanisation, mining and agriculture.
Habitat loss in its many forms has to go to the top of our political agenda instead of being ignored because it is politically too hard.
In comparison to other developed nations, Australia is the worst performer and habitat loss proceeds at a far greater speed than any protective measures. The south west is amongst the most threatened ecoregions.
Hundreds of high-profile scientists have recently warned our governments to tighten land clearing laws to stop the devastation of habitats – so far these alarm bells have been ignored. (Watson et al, 2016)
For the human population, Busselton is one of the fastest growing regions in Australia while the loss of habitat for ringtails has been just as staggering and this trend is unlikely to ease any time soon.
In the urban context core habitat areas near the foreshore are now either expensive real estate or sought after leisure and sporting areas.
Large fertile areas in the surrounds which would have also provided good habitat values have been cleared for agriculture, while Wayne (Wayne et al, 2006, Wayne et al, 2000) pointed out the negative effects of habitat loss caused by clearing in forests.
Even if habitat was well protected in the so-called conservation estate, this would not be sufficient to hold the decline trend of the species, let alone allow recovery and long-term viability. (Wayne et al, 2006)
There are hardly any large areas with good habitat left but not even poorer quality remnants are spared destruction. If not lost completely, they are fragmented. (Wayne et al, 2006)
Human induced fragmentation of habitats poses one of the most immediate threats to global biodiversity and is defined as the division of continuous habitat into patches without connection. This not only creates small and possibly non-viable remnants but potentially alters their shape and isolates them from other similar habitat areas by areas that are of no or very limited use to some species. (Frazer et al, 2015)
Irregularly shaped patches and small remnants are influenced by edge effects. The edge of a habitat is obviously more prone to disturbances than a large, continuous area.
Habitat edges are more at risk of weed invasion which then might suppress native plants. (Frazer et al, 2015) Elevated predation rates at habitat edges have been reported in many studies and would increase the necessity for frequent baiting which might however be particularly difficult to achieve in a small patch near human habitations.
Fox control for instance also appears less effective in a highly fragmented landscape. (Wayne et al, 2006)
In contrast to this, Harring-Harris noticed no repercussions for arboreal marsupials through edge effects if proper maintenance and conservation methods are in place; however she does not explain which methods she is referring to. (Harring-Harris, 2014)
Even if the area that is cleared is not large the smaller remaining fragments will support less individuals than a contiguous habitat patch of the same (combined) size would. While fluctuation near carrying capacity is normal for contiguous habitat, small fragmented populations can quickly fall below minimum viable population size.
With increasing fragmentation the extinction risk will also increase and conservation biology has identified fragmentation as a major driver of extinction. (Bradshaw, 2008)
An increase in predator abundance seems a definitive risk in fragmented habitats which would then compound the impact of the loss of habitat and could render it unsuitable for vulnerable animals like ringtail possums. Generalist predators such as foxes and cats seem to particularly thrive in human-modified landscapes. (Graham et al, 2012, Lindenmayer and Fisher, 2006)
Fragmentation due to access tracks and roads also allows greater access by feral predators and they prefer moving along tracks instead of through denser vegetation.
Fragmentation isolates populations which paired with the lack of dispersal opportunities increases the risk of inbreeding and inbreeding depression.
Reduced genetic diversity will in the long run weaken the population and its resilience to withstand other threatening processes possibly past an ecological threshold when adaptation to changing environmental conditions becomes impossible. (Eldridge and Herbert, 2015)
Any clearing can cause physical trauma to the animals and direct mortality for instance through collision with machinery or cars when trying to flee in addition to the long-term impacts.
Negative effects from clearance can also be delayed. Dewatering of vegetation, disturbance of soil leading to severe degradation of the area seem to just be seen as collateral damage.
In a suboptimal ecosystem even small changes can exacerbate a decline trend. Clearing a few more trees would not have much of an impact on its own but the cumulative impact from all those minor clearings in an area can lead to a major decline in a population and even to local extinctions. However, every development is investigated in isolation – if at all – and some argue that our ringtails will suffer death by a thousand cuts as every single event is not regarded as objectionable.
The myriad of exemptions where no impact assessment is required and the lack of a government register of all clearing events (EPA Annual Report 2015-2016) might give us the illusion that threats are well managed while even the extent of them is basically unknown.
