The dietary preferences of koalas,Phascolarctos cinereus, in southwest Queensland

Abstract

The koala population in southwest Queensland is a large low-density population of important conservation value which is vulnerable to habitat loss, drought and climate change. The nutrient quality of Eucalyptus food trees favoured by koalas is an important factor influencing the survival of the koala on a low-nutrient-and-high-toxin diet. This study investigated the relationship between the diet of koalas, and food tree characteristics. Vegetation surveys, cuticle analysis and leaf chemical analysis were conducted in 14 study sites in southwest Queensland during the winter of 2010. Koala diet composition was different to eucalypt tree species availability, with Eucalyptus camaldulensis (56.5%) the most important tree species, E. coolabah (15.4%) and E. populnea (12.4%) of secondary preference. Leaf chemicals (moisture, total nitrogen, total phenolics, and a nutrition index = (moisture*nitrogen) / total phenolics) were significantly related to tree species, surface water availability, soil type and proximity to major creeks. Only leaf moisture was significantly correlated with koala food tree species preference. The presence of surface water appears to be a crucial characteristic of suitable koala habitat while riparian habitats dominant by E. camaldulensis are critical for conserving the koala populations in southwest Queensland.

Determining range edges: habitat quality, climate or climate extremes?

“…We calculated the proportion of primary and secondary habitat in each landscape, as previous research has found that the amount of high-quality habitat is important for koalas in Queensland and New South Wales Smith et al, 2013a). Primary habitat was dominated by E. camaldulensis, which forms the majority of the koala's diet and tree use in this region (Seabrook et al, 2011;Wu et al, 2012). Secondary habitat was dominated by E. coolabah, E. populnea, E. ochrophloia and E. thozetiana.…”

Influence of leaf chemistry on dietary choice and habitat quality of koala (Phascolarctos cinereus) populations in southwest Queensland

“…Previous studies have found that the water content of eucalypt leaves across Queensland ranged between 39-65% wet weight (Munks et al 1996, Ellis et al 2002, Clifton 2010, Wu et al 2012.…”

“…Water availability to trees varies both spatially and temporally which influences leaf chemistry in different ways. In semi-arid areas of Queensland, Eucalyptus trees occurring along creek-lines, where more folivores also occur, had higher leaf moisture than in trees growing far from creek-lines (Munks et al 1996, Wu et al 2012). In addition, presence of surface water was positively associated with leaf moisture (Wu et al 2012) and surface water can make up to 50% of the water source to trees when it is available in long-term .…”

“…In contrast, there is little research on the leaf chemistry of trees used by semi-arid koala populations which are vulnerable to seasonal and inter-annual rainfall variations (Gordon et al 1988). My previous study (Wu et al 2012) was the first leaf chemistry study for the semi-arid koala populations in southwest Queensland but it was limited to one season. Furthermore, there is an absence of studies of how the leaf chemistry of the same tree species varies at the landscaperegional scale with environmental variability, especially climate variability and surface water availability.…”

“…Different genotypes, which are the genetic constitutions of organisms (Allaby 2012), can lead to variations of foliar chemistry along taxonomy, among individuals and even within one plant , Youngentob et al 2011, Padovan et al 2012. The variation of leaf moisture between tree species has been studied in semi-arid and sub-humid areas, and showed interspecific variation (Munks et al 1996, Wu et al 2012, Melzer 1995. There are more studies of the variation of nitrogen and PSMs within Eucalyptus taxonomic divisions.…”