Post-fire succession affects abundance and survival but not detectability in a knob-tailed gecko
Highlights
► Mark-recapture modelling showed no effect of post-fire succession on detectability. ► Abundance increased for up to 9 years after fire then declined. ► In recently (<3 years) burnt sites survival was lower, but fecundity was higher. ► Successional changes in predation, thermoregulation and resources are likely causes.
Introduction
Disruption of natural fire regimes from modern human land use has contributed to the decline of animal populations in many ecosystems around the world (Betts et al., 2010, Gregory et al., 2010, Lyet et al., 2009, Pardon et al., 2003, Sanz-Aguilar et al., 2011). Fire is widely used to create successional diversity in vegetation under the often untested assumption that this will benefit biodiversity more broadly (Parr and Andersen, 2006). However, if this practice is conducted at inappropriate spatial and temporal scales, animal populations may face local extinction (Bradstock et al., 2005, Templeton et al., 2001).
Well studied changes in plant demography after fire have led to conceptual and simulation based models to predict the effects of different fire regimes on vegetation (e.g. Bradstock et al., 2006, Moreira et al., 2009). Although there has been some progress in this direction for animal species (e.g. Bradstock et al., 2005) development has been slower than for plants because of the difficulty in obtaining animal life history data (Clarke, 2008). At the community level, a functional trait-based approach for predicting fire responses in plants (e.g. Keith et al., 2007) holds promise for use in animal studies (Langlands et al., 2011, Moretti et al., 2009). However, this approach requires detailed information on life history traits, including survival, reproduction and dispersal (Langlands et al., 2011) which are not available for most animal species in fire-prone ecosystems. Understanding demographic changes of animal populations after fire is critical if we are to develop a predictive framework for ecological fire management (Clarke, 2008).
Post-fire succession in animal communities has traditionally been explained by a habitat accommodation model where the peak density of an animal species is correlated with that of its optimal post-fire habitat (Fox, 1982). However, fire-related patterns of abundance often vary spatially or temporally within species making simple habitat models unreliable (Driscoll and Henderson, 2008, Lindenmayer et al., 2008). Understanding the causes of fire-related changes in abundance will allow more accurate predictions of the effects of fire regimes on animal populations (Driscoll et al., 2010, Whelan et al., 2002). The profound habitat changes caused by fire are likely to influence survival in animal species by changing predation rates, food availability, reproductive success and thermal environments (Hawlena et al., 2010, Hossack et al., 2009, Le Galliard et al., 2005, Pike et al., 2010). Recent evidence shows that modified fire regimes can affect animal survival (Lyet et al., 2009, O’Brien et al., 2003, Pardon et al., 2003) highlighting the need for a taxonomically and ecologically broader understanding of successional changes in survival rates of animals.
While developing a trait-based approach to fire management is crucial, quantifying the effects of fire on animal abundance remains fundamental to fire ecology. Ecological fire management plans are usually based on empirical observations of apparent differences in abundance of target species in habitats of different time since fire (e.g. Petty et al., 2007, DENR, 2009). However, animals can also show behavioural responses to fire-driven succession (Fenner and Bull, 2007, Vernes and Haydon, 2001), meaning that detectability could change with time since fire. If this is true, descriptions of animal fire responses based solely on counts may not represent actual abundance, leading to misguided management (White, 2005). Despite this concern very few studies have controlled for detectability when investigating the effects of fire on animal abundance (Driscoll et al., 2010).
Driscoll and Henderson (2008) estimated abundance from counts to identify common reptile species with local distribution patterns influenced by post-fire succession in mallee woodlands of southern Australia. One of these was the starred knob-tailed gecko, Nephrurus stellatus, which they reported to show a strong fire-specialist response, with higher abundance in early than late successional habitats (Driscoll and Henderson, 2008). In this study we collected 2 years of mark-recapture data from N. stellatus to determine if (1) apparent effects of succession on abundance were confounded with fire related detectability differences, and (2) monthly survival rates differed with time since fire and could therefore account for observed differences in abundance. We also examined if post-fire succession affected three measures of reproductive capacity (age structure, sex ratio and female reproductive status) to help further explain any observed fire effects on abundance and survival. Our aim was to understand demographic responses to fire in a species that is likely to be sensitive to variation in fire regimes. Through this process, we sought to advance fire research on animals by developing a causative understanding of succession using biologically meaningful models of detectability.
Section snippets
Study system
The study was conducted at Hincks Wilderness Area and Pinkawillinie Conservation Park on the Eyre Peninsula, South Australia (Fig. 1). The region is semi-arid, with an average annual rainfall of 322 mm. The main topographic features are white siliceous sand dunes, occurring in either large, parabolic fields or longitudinal ridges over calcrete limestone (Twidale and Campbell, 1985). Hincks and Pinkawillinie are dominated by mallee woodlands where low, multi-stemmed Eucalyptus species
Capture summary, reproductive capacity, and robust design assumptions
We recorded 532 captures (308 individuals, 224 recaptures) at Hincks and 215 captures (139 individuals, 76 recaptures) at Pinkawillinie (Appendix A). There was no effect of fire category on the age structure or sex ratio in either season or location (Fisher’s exact tests P > 0.05, Appendix B). The proportion of females that were gravid was significantly higher in the early (93.8%) than the medium fire category (56.5%) in season two at Hincks (Fisher’s exact test P = 0.01, Appendix B). Data from
Post-fire abundance and detectability
Ignoring detectability in ecological studies can lead to spurious results and misguided management (White, 2005). Fire regimes can influence detectability in mammals (Pardon et al., 2003) raising concerns about conclusions drawn from simple count data in fire ecology studies. We asked whether the early successional distribution of the gecko N. stellatus reported by Driscoll and Henderson (2008) was biased by differences in detectability among post-fire successional stages. Our mark-recapture
Conclusions
Given the recent severe changes in land use, ecological fire management must be conducted on temporal and spatial scales that are appropriate to the contemporary landscape (Keith and Henderson, 2002). In Australia, most mallee vegetation has been cleared for agriculture and small habitat remnants (approx. 1000 ha) can be completely incinerated by unplanned fire (DENR, 2011), which may disadvantage late successional species (Driscoll and Henderson, 2008). Prescribed burning may therefore be
Acknowledgements
Assistance with field work was warmly received from J. Atamanik, S. Barnes, D. Barry, B. Berthelot, S. Blight, J. Bradley, A. Castañeda, S. Chubb, K. Coley, S. Dalgairns, A. De Costa, R. Dudaniec, L. Fazzalari, A. Fenner, K. Griffiths, I.J. Hagen, T. Hague, A. Hodgson, A. Johnston, S. Juárez, J. Lazzari, T. Ling, N. Maurovic, K. Mayes, K. McCallum, G. McLachlan, S. Morley, I. Motzke, T. Moyle, A. Murphy, K. Pelgrim, A. Quarmby, S. Scrivens, N. Shea, J. Simons, S. Smith, S. South, T. Suich, A.
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