You Could Be Your Worst Enemy's Best Friend - Part 2: The Quoll

So how is it that the poor planigale can be the best friend of it's worst enemy? We are getting there (I promise), but the scene must first be set.

Teaser: I believe that the planigale is to the Koolan Island Northern Quoll what Will Smith was to the citizens of New York. A glimmer of hope at the dawn of the Cane Toad apocalypse. As we all know, it is always darkest before dawn. Before the hero (Mr Planigale) can rise up and save the innocents (the quoll) many hundreds of those innocents will perish; slowly, painfully.

News Flash: Quoll populations have been decimated as a result of their predation on Cane Toads since Day 1 of the toads introduction into Australia. Quolls are relatively big, hungry predators that have an insatiable appetite. They eat toads and they die. You don't have to dig too deep to bury yourself under mountains of literature supporting this statement. In fact, you should check out the work of the Shine Lab; it is freakin' awesome.

Background: Cane Toads have not caused the extinction of any species of Australian native fauna, but they sure as hell have given local populations of certain species, such as quoll, a bloody good dose of 'what for' and then some. Despite the reality that localised extinctions of some discrete populations of some species are probably far more common than we know, the fact remains that Cane Toads have NOT wiped out entire Australian native species across the entirety their distribution.

Like most of our wily and highly evolved  native fauna, the Northern Quoll is not stupid and it is a survivor.

Back to our story.......

Cane Toad eggs have lots of poison and big toads have a lot of poison (Hayes et al., 2009). So if you are going to eat Satan's line backers (big ugly adult Cane Toads) or the spawn of Satan (the eggs) you are in real trouble. Quoll don't eat the eggs, but because of their size, ability to subdue prey and their need to feed adult quoll will tackle adult toads and they die as a consequence.

You don't need to be a rocket scientist to appreciate the fact that the biggest Quoll will take on the biggest Toad if it thinks, but for a second, that Mr Toad is going to be an easy, wholesome meal that won't put up too much of a fight. As an extension of that, you don't need to be brain surgeon to understand that smaller quoll will tackle smaller toads.

The tremendous advantage that Koolan quoll have over their mainland conspecifics, in the race to survive the invasion of the toad, lies in their morphometrics. Mainland Northern Quolls can weigh up to 1.2 kg, with the males (400 to 900 g) being larger than the females (300 to 500 g) (Braithwaite & Begg 1995). On Koolan Island males average only 548g and females average 298g. Let me put that into perspective visually. The first photo is a 200grm female and the second photo is a 900grm male. You can see the size difference and you can imagine the marked difference in the size of the toads each of these two quoll would tackle.

So for those of you that are still with me you will immediately recognize that Koolan quoll will have a much better chance of surviving a Cane Toad invasion because the quoll themselves are smaller and therefore the toads that they will attack and eat will be smaller and therefore less poisonous. Many will die, of course, but many may not and there is a bucket load of literature out there supporting the idea that savvy quoll will quickly learn to avoid toads if they manage to survive their first encounter. It is those savvy quoll that will continue to procreate in spite of the Cane Toad apocolypse that will descends over Koolan Island like a cloud of lead laden dust.

Enter Mr Planigale.....the real hero of this tail.



References:

Braithwaite, R. W. & R.J. Begg (1995). Northern quoll Dasyurus hallucatus Gould, 1842. In: Strahan, R., ed. The Mammals of Australia: National Photographic Index of Australian Wildlife. Page(s) 65-66. Sydney: Reed Books.

Hayes, R. A., M. R. Crossland, M. Hagman, R. J. Capon, and R. Shine. 2009. Ontogenetic variation in the chemical defences of cane toads (Bufo marinus): toxin profiles and effects on predators. Journal of Chemical Ecology 35:391-399.

Webb, J. K., G. P. Brown, T. Child, M. J. Greenlees, B. L. Phillips, and R. Shine. 2008. A native dasyurid predator (common planigale, Planigale maculata) rapidly learns to avoid toxic cane toads. Austral Ecology 33:821-829.