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Riverine health is not just about in-stream condition, as the biota in our rivers and wetlands is very dependent on the surrounding terrestrial environments.
Of particular influence, and disproportionately imperiled, are the riparian zones – that narrow strip along rivers and streams and around wetlands that supports a terrestrial biome that is directly dependent on the adjacent water. A range of species of bird, reptile and amphibian depend on riparian zones, and some are found there and nowhere else.
The eastern water dragon, Physignathus leseuerii, is one such species. These are large lizards, up to 80 cm long, robust, and fairly conspicuous. They often rest on overhanging branches, only to drop in a swan dive head first into water when disturbed. Often the splash is what attracts attention, by which time it is too late to see the animal, and it will remain submerged for up to two hours before surfacing, confident that the danger has passed.
When surprised on land, water dragons do a spectacular bipedal dash – up on their hind legs they do a dinosaur impersonation in miniature, presumably gathering that added speed that makes all the difference between capture and escape.
Insectivorous when young, omnivorous as adults, they are responsible for dispersing a wide range of seeds which survive their guts and germinate where they deposit their faeces. How important this is for riparian seed dispersal is not known.
These lizards have another claim to fame – the sex of their offspring is determined by incubation temperature. Female babies hatch out of their eggs if they are incubated at either high or low temperatures, and males are produced only at intermediate temperatures.
One would think this would make them extraordinarily vulnerable to climate change, but they have been around for a long time and as a species, have no doubt experienced changes in climate as great or greater than we are currently experiencing, albeit perhaps not so fast. The challenge for us is to work out how they have accommodated climate change in the past, and what we are doing to the environment that might constrain their options for the future. Species such as this could be a key early indicator of the impacts of climate change on our inland waters and associated riparian ecosystems.
By Arthur Georges , Professor in Applied Ecology and
Dean of Applied Science, Institute for Applied Ecology, University of Canberra