Reptile dispersal and demography after fire : process-based knowledge to assist fire management for biodiversity

Abstract

The disruption of natural fire regimes has threatened animal species in many ecosystems around the world. A combination of prescribed burning and fire suppression is often used to promote successional variation in vegetation (i.e. fire mosaics), with little knowledge of how this will affect animal persistence. Understanding the processes that govern species responses to fire regimes is essential to build a predictive capacity for ecological fire management. I examined life-history, demographic (survival, reproduction and mortality) and dispersal attributes of reptiles to investigate mechanisms of fire responses in reptiles. I studied reptiles in conservation reserves of semi-arid southern Australia dominated by mallee vegetation (multi-stemmed Eucalyptus spp. with a shrubby understory). An introduction describes the ecological and management context of my research (Chapter 1). A community-level framework was used to determine if a generalised model of fire responses could be developed based on traits shared by groups of species (Chapters 2-3). I found a number of fire responses in reptiles that were previously undetected in analyses of smaller, but substantial subsets of the same data (Chapter 2). Nocturnal burrowers tended to be early-successional, while diurnal leaf-litter dwellers tended to be late successional, but a trait-based model of succession had limited power to describe responses among the community. I also documented some observations that suggested non-burrowing reptiles were more vulnerable to mortality during wildfire than burrowers (Chapter 3). A species-level framework was then used to examine variation in demographic and dispersal attributes within species among different post-fire successional stages (Chapters 4-7). These studies focussed on three species with significant and contrasting responses to fire: Amphibolurus norrisi (Agamidae; mid/late successional species), Ctenotus atlas (Scincidae; late successional) and Nephrurus stellatus (Gekkonidae; early/mid successional).

Using mark-recapture modelling (Chapter 4), I described changes in abundance of N. stellatus that incorporated detectability, and showed that variation in survival and fecundity are possible drivers of this species strong population response to fire. Microsatellite DNA data were then used to examine gene flow in the three target species and gain insights into the effects of fire on dispersal. Chapter 5 begins this section with a description of the markers I used to generate the genetic data. I then used spatial models of landscape resistance to assess the importance of post-fire succession and other landscape features (e.g. topography) on gene flow in the three species (Chapters 6 and 7). For N. stellatus these analyses were combined with direct observations of movement (Chapter 6). Results showed that long-unburnt vegetation restricts dispersal in N. stellatus, which may result from, or contribute to its decline in population density with increasing time since fire. In Chapter 7 I found that fire affected gene flow in A. norrisi, but not in C. atlas, while genetic diversity in both species was affected by post-fire succession.

My thesis demonstrated how examining demographic and dispersal attributes of reptiles can give insights into the mechanisms underlying species responses to fire. I concluded by providing management recommendations and highlighting key points for future research on fire ecology (Chapter 8). -- provided by Candidate.