Document ID: chunk:federal_register_of_legislation:F2022L00555:body:0:p60
Version: federal_register_of_legislation:F2022L00555
Segment Type: other
Provision Reference: 
Character Range: 190103–193141

movement patterns (McAlpine et al. 2006b; Rus et al. 2021). Chronic stress to Koalas from these factors is thought to also increase their susceptibility to disease (Davies et al. 2013; Narayan and Williams 2016) (Figure 4).
Extinction debt (Tilman et al. 1994), whereby the local loss of Koala populations after habitat loss has tipped over the threshold for long-term persistence, can take up to 100 years to manifest itself (Seabrook et al. 2014b). Random fluctuations or perturbations in population growth rates due to chance events of individual mortality and reproduction (demographic stochasticity or drift) or environmental stochasticity (e.g. natural catastrophes) are exacerbated in isolated populations (Soulé et al. 1986). These processes have led to local losses of Koala populations (TSSC 2012a) such as reduction of Koala populations throughout its urbanised coastal range (Seabrook et al. 2014b).

20.2 Habitat degradation
The key threats driving habitat degradation for the Koala include timber harvesting using silvicultural systems that do not retain habitat trees; agriculture; altered hydrological regimes from land clearing, soil erosion and water extraction (Cowie et al. 2007); fire and fire management; and climate change (TSSC 2021). Direct threats such as climate change and land clearing can also interact with other threats such as invasion by weeds and pathogens, potentially increasing the impact. Habitat degradation reduces the availability or increases the mortality of food and shelter trees, reduces the nutrient value and water content of food trees, and changes the configuration and relative abundance of habitat trees. These changes impact Koalas by making it more difficult for them to find food and shelter resources, increasing stress levels and disease, and leading to reduced breeding success and increased mortality. Habitat degradation is common in landscapes that are also subject to progressive land use change. It can lead to habitat loss as native vegetation is slowly changed to a composition and structure that no longer resembles the original state (Lindenmayer and Fischer 2006). Habitat degradation also reduces availability and quality of resources for species and can drive population declines over the long term (extinction debt, Tilman et al. 1994).

20.3 Genetic effects
Land use change also adversely affects the genetic structure of populations by eroding genetic diversity and increasing genetic differentiation (Charlesworth and Charlesworth 1999; Thompson 2006). As populations become more isolated in smaller remnants that are disconnected, gene flow tends to decrease. The resultant smaller populations are more prone to the effects of genetic drift and inbreeding (Bouzat 2010; Hedrick and Fredrickson 2010). Indeed, Koalas do not appear to exhibit inbreeding avoidance behaviour, a characteristic thought to making them vulnerable to inbreeding (Schultz et al. 2020), although they do appear to exhibit mate choice based on genetic variation at the MHC region (Brandies