Niche construction and Dreaming logic: aboriginal patch mosaic burning and varanid lizards (Varanus gouldii) in Australia

Abstract

Anthropogenic fire is a form of ecosystem engineering that creates greater landscape patchiness at small spatial scales: such rescaling of patch diversity through mosaic burning has been argued to be a form of niche construction, the loss of which may have precipitated the decline and extinction of many endemic species in the Western Desert of Australia. We find evidence to support this hypothesis relative to one keystone species, the sand monitor lizard (Varanus gouldii). Paradoxically, V. gouldii populations are higher where Aboriginal hunting is most intense. This effect is driven by an increase in V. gouldii densities near successional edges, which is higher in landscapes that experience extensive human burning. Over time, the positive effects of patch mosaic burning while hunting overwhelm the negative effects of predation in recently burned areas to produce overall positive impacts on lizard populations. These results offer critical insights into the maintenance of animal communities in the desert, supporting the hypothesis that the current high rate of endemic species decline among small animals may be linked to the interaction between invasive species and mid-century removal of Aboriginal niche construction through hunting and patch mosaic burning.

Figure 1.

Flowchart illustrating the hypothetical process through which Martu hunting and burning affects sand monitor population density. Over the long term, human burning reduces mean fire size and increases diversity of regrowth patches across the landscape, increasing habitat edge density and providing positive feedbacks to V. gouldii populations. At the same time, human predation removes V. gouldii from recently burned areas (providing a negative feedback effect), but also removes V. gouldii predators (providing an indirectly positive effect).

Figure 2.

Sand monitor density increases with use rank in unburned patches, but reaches an intermediate peak in burned patches. Varanus gouldii density is measured as the mean (±95% CI) proportion of sample plots in both previously burned (within 5 years) and unburned (greater than 5 years since fire) patches with at least one burrow present. Density is plotted against use rank (ranked by forager-hours per square kilometre). There were a total of 368 plots located in regions assigned to use rank 4, 2921 in use rank 3 regions, 4282 in use rank 2 regions and 607 in use rank 1 regions.