Hunting and
Feeding: Koala (Phascolarctos cinereus)
The koala is a small, grey,
bear-like marsupial with characteristic pale ear tufts that lives in eucalyptus
forest and woodlands in Eastern Australia and grows to about 72-78cm in length
(White, 1999). Equipped with powerful forelimbs, opposable digits and strong
claws, koalas are able to move through the trees to reach their food with ease,
which they then nip of with their sharp incisors (Uhlenbroek, 2008). They have
also adapted modified cheek teeth; a single premolar and four molars with high
crowns on each jaw, enable them to grind the tough leaves into a smooth paste
for digestion (White, 1999).
Young koalas, after emerging from
the pouch, eat a small amount of its mothers ‘pap’; which is a specialized form
of faeces that is soft and runny (Uhlenbroek, 2008). This pap is a rich source
of protein for the growing koala and also introduces the bacteria needed to
digest eucalyptus leaves, into the young koalas system (Cork et al, 1983).
While occasionally browsing on other tree
species, koalas tend to feed almost exclusively on the fibrous leaves of
eucalyptus trees (Cork et al, 1983).
Eucalyptus leaves are low in protein, high in toxins and extremely hard to
digest (Cork et al, 1983). However,
the digestive system of the koala has been specifically adapted to deal with
this challenge; the enlarged caecum – which at about 2m long is the biggest of
any mammal or marsupial – is the site at which the toxins are deactivated and
the paste is digested by bacterial fermentation (Uhlenbroek, 2008). This then
allows the koala to survive on a diet consisting exclusively of eucalyptus
leaves (Cork et al, 1983).
However, this tolerance to
eucalypt leaves comes with a price; due to the challenging nature of digestion,
Koalas spend almost 100% of their day sleeping and are often prone to disease
(White, 1999). Furthermore, the singular diet of koalas is extremely limiting,
as forests and woodlands containing eucalyptus trees are destroyed, the koala’s
habitat and sole food source are destroyed along with them, leaving this native
Australian icon in need of serious help (White, 1999).
References:
Cork, S. J., Hume, I. D. & Dawson, T. J.
(1983). Digestion and metabolism of a natural foliar diet (Eucalyptus punctata) by an
arboreal marsupial, the koala (Phascolarctos cinereus). Journal of Comparative Physiology, 153(2),
181-190.
Uhlenbroek, C. (2008). Animal Life. Penguin Group, UK.
White, N. A. (1999). Ecology of the koala (Phascolarctos
cinereus) in rural
south-east Queensland, Australia. Wildlife Research, 26(6), 731-744.
Hi Michaela. Interesting post. Just wondering how similar are the Greater Glider's adaptations for dining on Eucalyptus species? Cheers.
ReplyDeleteA nice interesting example this week. However, I am curious. Why would such a (seemingly) costly dietary strategy evolve? If these koalas suffer a cost of increased disease susceptibility, what benefit are they gaining that outweighs this cost? Interesting.
ReplyDeleteThe kola certainly has a strict diet. Do these bacteria in the gut help the kola retain more protein from the eucalyptus? If not, do kolas generally need little protein to metabolically function- and if so, how? Great post!
ReplyDeleteSorry for the late reply guys! Firstly both the koala and greater glider share the same enlarged caecum that allows the fermentation of the eucalyptus leaves. Secondly, I agree with the odd nature of koalas eating only eucalyptus leaves when there is such a high cost involved, however because of the toxic nature of the leaves most other herbivores cannot digest them and stay away, therefore allowing the koala to dine on these leaves without having to compete with other species. And lastly, the bacteria in the gut help to break down the leaves where no other animal can do the same, but the leaves themselves contain all the dietary needs the koala requires, containing 50% water, 18% fibre, 13% tannins, 8% fat, 5% carbs, 4% protein and 2% minerals. I hope I have answered everyone's question satisfactorily :)
ReplyDelete