The Most Diverse Lizard Community on Earth

Seeking the origins of biodiversity in Australia’s deserts

by Daniel L. Rabosky

The author with a juvenile yellow-spotted monitor in the Great Victoria Desert, Australia.

Photo by Brett Lewis

It is dusk in Australia’s Great Victoria Desert. The white, ghostly gum trees glow crimson for several minutes before the summer sun slips beneath the western horizon. The birds have settled down for the evening, but mornings are hustle and bustle as dozens of pink and gray Galahs jostle with Ring-necked Parrots for a turn at the tiny pool of water near our field station. Handsome Zebra Finches descend by the hundreds, while ever-opportunistic butcherbirds watch the proceedings from a distance.

Never have I seen such a land of paradox. Despite a nearly complete absence of surface water for much of the year, the interior deserts of Australia harbor incredibly diverse assemblages of plants and animals. Bird diversity is higher than in any comparable arid region on the planet. But it is the lizards that truly steal the show: up to 56 species have been found living together at sites in the Great Victoria Desert!

I’m a Ph.D. student in the Evolutionary Biology Program at the Cornell Lab of Ornithology. My research has two main objectives. First, I’m trying to understand why so many lizard species are packed together in the Australian deserts. Second, I want to know why some groups of animals become so much more diverse than other groups. Here in Australia, the majority of lizard species at a given site are skinks. And some groups of skinks are phenomenally diverse: my research focuses on two genera that contain at least 100 species each, most of which live in Australia’s arid regions.

One of the most bizarre inhabitants of the Australian deserts: the thorny devil. These common but exceedingly well-camouflaged lizards eat ants almost exclusively.

Photo by Daniel L. Rabosky

Why lizards and not birds? If we are to understand the general evolutionary and ecological processes that shape the world in which we live, we will need evidence from many, many groups of animals. It is the richness of the fauna—and especially the skink fauna—that makes this system so special. With this level of diversity, we can ask questions that simply can’t be addressed in other systems. Because there are so many closely related lizard species living together, we have tremendous statistical power to tease apart subtle ecological mechanisms—mechanisms that will ultimately help us understand, for example, why certain sets of warblers are found together in beech-maple forests in the northeastern United States. And by studying the evolutionary explosion of skink species in Australia, we might better understand other “adaptive radiations”—when opportunities for ecological specialization drive rapid species proliferation, as has occurred in Hawaiian honeycreepers and Galapàgos finches.

The Wedge-tailed Eagle is common along roadsides in arid Australia, where they feast on the abundant roadkills. This one has found a red kangaroo.

Photo by Daniel L. Rabosky

My daily routine is predictable: I sample lizard populations using pitfall traps. To set up a pitfall trap grid, I bury five-gallon buckets in the sand and connect rows of buckets with a fine mesh fence. Lizards (and large venomous centipedes and scorpions) run along the fence until they fall into the buckets. I leave the traps open all day and all night, checking them often to minimize stress to trapped animals. I take ecological data on each animal and tissue samples from many (often a tail tip). This method is a great tool for determining which species live in particular habitats, as well as the relative abundances of species within those habitats. When I return to Cornell, I’ll analyze the DNA sequences from these animals to unravel their evolutionary relationships. Deeper scientific issues aside, pitfall trapping is just plain fun. Hands-on interaction with so many amazing animals every day reminds me of why I became a biologist in the first place.

One of the benefits of extended field study is that you see many natural phenomena that generally would be missed by a casual visitor. A particularly memorable moment occurred in late December, when temperatures at one of my field sites exceeded 120° F. It was so hot that birds—native desert birds—were dying. At a small waterhole, I watched hundreds of Australasian Magpies, Bourke’s Parrots, and other birds panting from heat stress, beaks agape. Normally graceful honeyeaters waddled on the ground, sufficiently heat-addled that they appeared to be unaware of my presence. At the edge of the water, Zebra Finches drank fearlessly next to their usual enemy, the Brown Goshawk. The next day, I found many dead birds that had not been so lucky to find water. Apparently, such mortality is not uncommon in the Australian deserts, and it is a testimony to the remarkable resilience of birds that they can rebound from such events to fill our mornings with song.

It is late, and I must hurry to finish taking data on some animals captured earlier in the day. As usual, I’m already excited about waking to a morning of windswept sand dunes, emus, kangaroos, and lizards, lizards, lizards….

A Pied Butcherbird, the author’s favorite bird. Butcherbirds are inquisitive and intelligent, and their flutelike melodies may be the most beautiful sounds in the deserts. Rabosky often watched them foraging for lizards and large insects near his campsite.

Daniel Rabosky is a Ph.D. candidate in the Department of Ecology and Evolutionary Biology at Cornell University and in the Lab of Ornithology’s Evolutionary Biology Program.

Dan’s research is supported—financially, logistically, or through collaboration—by the Western Australian Department of Conservation and Land Management, the National Science Foundation, the Australian Academy of Science, the Western Australian Museum, the South Australian Museum, the Mario Einaudi Center for International Studies, and Sigma Xi.

For permission to reprint all or part of this article, please contact Miyoko Chu, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-2451. email: mcc37@cornell.edu