Lessons in biogeography (from the back seat of a Datsun station wagon)

Road trips of my youth rarely entailed music. My siblings and I cruised the highways of south-eastern Australia mostly in silence. Melbourne to Bright – silence. Melbourne to Barmah – silence. Melbourne to Canberra – silence. Melbourne to Mildura – silence.

It wasn’t enforced – I didn’t grow up in some sort of ‘Footloose’ inspired cult family in which the revelry of music was considered sacrilege. My father, who was invariably driving, merely preferred quiet contemplation and the joy of the drive. Or at least that’s what I presume; the truth is I’ve never actually asked.

Whatever my father’s motivations, the outcome for me was profound. Our family holidays were invariably north, away from Melbourne to more xeric climes. We wandered the Hume, the Calder, the Northern and the Newel, seeking out rivers and lakes across the great expanse of the Murray-Darling Basin. From the cool mountain streams in the upper catchment, to the languid lower reaches of the Murray and Darling Rivers themselves. The thing is, as you cruise through these landscapes in silence, you take more in. You notice the change from White Box to Grey; the first appearance of Buloke; the disappearance of Cassinia and the appearance of chenopods. You absorb the landscape, subtly and osmotically. As the kilometres fall away, the great tapestry of biogeography is revealed.

Take Triodia. My first sighting of this extraordinary grass remains etched on my mind. Triodia – or Spinifex as it is more commonly known – is perhaps the singular success story of the Australian Outback. It occurs over literally millions of hectares of the most arid and desolate terrain Australia has to offer. My fascination with this grass is not (I must admit) with it per se, but rather with the animals it houses. For Triodia hummocks are a remarkable store of lizards. You may know that Australia’s deserts have some of the highest densities of lizards in the world, both in terms of abundance and species diversity. You may not know that Triodia is a key driver of this, at least according to some. Its hummocks provide seemingly perfectly designed lizard lairs, complete with a protective shroud of spiny foliage, cool and stable microclimates and an abundance of juicy invertebrate prey.

It was somewhere around 20 km north of Ouyen in the Victorian Mallee where I caught my first glimpse of Triodia. We’d been driving up the Calder Hwy for hours – probably five by that stage – on our way to Mildura. I’d been watching the vegetation change from tall forest to Box-Ironbark to Mallee, through various shades that entailed evermore diminutive Eucalypts. Now we were approaching proper sand dunes, and I knew that Triodia was on the cards. Then, sure enough, on cresting a dune of previously unrivalled proportions, there it was. A hummock. A Spinifex hummock! In the flesh, whizzing past my window. I craned my neck and watched it until it disappeared from view.

Whipping back, I looked for more. It took time, perhaps another 5 km, and then I spotted another. Then another and another, until they were carpeting the ground. We’d hit Hattah-Kulkyne National Park and the blessed things were everywhere.

To this day, I think about that sole hummock, a good 5 km from its nearest brethren. Was it the most southerly hummock in that region? If it wasn’t, then such a hummock must have existed, out there, somewhere. And if that is true, then it is also true of every species in the world. All must have one individual, at any one point in time, that is the most far flung member of its species. One intrepid individual pushing the limits of the species’ range. What drives these boundaries? What holds them in place? Is it thermal tolerances, or geological affinities, perhaps a deep-seated fear of frosts or some mutualist that a species just can’t do without?

Ultimately, what I learned on those long, silent drives with my father is that this intrigue is eternal. Australia’s biodiveristy is immense and all species respond to environmental gradients uniquely. And anyway, ecosystems are forever changing and species distributions along with them. The search for biogeographic truths is endless, and it will always be so.

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