Where do animals come from during post‐fire population recovery? Implications for ecological and genetic patterns in post‐fire landscapes

Abstract

Identifying where animals come from during population recovery can help to understand the impacts of disturbance events and regimes on species distributions and genetic diversity. Alternative recovery processes for animal populations affected by fire include external recolonization, nucleated recovery from refuges, or in situ survival and population growth. We used simulations to develop hypotheses about ecological and genetic patterns corresponding to these alternative models. We tested these hypotheses in a study of the recovery of two small mammals, the Australian bush rat and the agile antechinus, after a large (> 50 000 ha), severe wildfire. The abundance of both species was severely reduced by fire and recovered to near or above pre‐fire levels within two generations, yet we rejected a hypothesis of recovery by external recolonization. While the agile antechinus showed genetic evidence for far greater dispersal capacity than the bush rat, neither species showed gradients in abundance or genetic diversity with distance from unburnt forest during population recovery. Population recovery was driven by local‐scale processes. However, the mechanisms differed between species, resulting from the spatial impacts of fire on habitat suitability. Agile antechinus populations recovered through population growth from in situ survivors. The bush rat followed a model of nucleated recovery, involving local recolonization from micro‐refuges in topographic drainage lines. Nucleated recovery by the bush rat was associated with changes in dispersal, and fine‐scale patterns of genetic admixture. We identified increased dispersal by females during recovery, contrasting with male‐biased dispersal in unburnt forest. Such flexibility in dispersal can potentially increase recovery rates compared to expectations based on dispersal behavior within undisturbed populations. Our study shows how the initial distribution of survivors, determined by fire effects on resource distribution, determines the subsequent scaling of population recovery patterns, and the sensitivity of population distribution and genetic diversity to changing disturbance regimes.

Bat activity before and after a severe wildfire in Pilliga forests: Resilience influenced by fire extent and landscape mobility?

“…We note that the riparian zones we sampled all burnt at high severity and this contrasts with gullies in moister forests where topography is complex (Banks et al . ). Similarly in flat semi‐arid woodland, proximity to unburnt vegetation, even small unburnt patches, enhances post‐fire occupancy of birds (Watson et al .…”

Wildfire refugia in forests: Severe fire weather and drought mute the influence of topography and fuel age

“…Unburnt patches within fire scars are considered important in facilitating the survival, persistence and recolonization of a range of plants and animals (e.g. Banks, McBurney, Blair, Davies, & Lindenmayer, ; Landesmann & Morales, ; Robinson, Leonard, Bennett, & Clarke, ). However, the definition of what constitutes fire refugia is scale‐ and context dependent (see Robinson et al, ); hence, our analysis will undoubtedly underestimate the availability of fire refugia.…”

Animal movements in fire‐prone landscapes

“…It is important to recognise that population responses to fire other than dispersal can have genetic consequences (Davies et al ., ). For instance, genetic differentiation among locations is commonly used as an indicator of gene flow (genetically effective dispersal) but can also be influenced by differences in effective population size (Prunier et al ., ), which can occur in landscapes with spatially heterogeneous fire regimes (Banks et al ., ). While this might pose a problem for drawing conclusions about dispersal from genetic data, we can refine our hypotheses by pairing empirical genetic data with simulation modelling of population processes.…”

“…Banks et al . () simulated alternative recovery mechanisms for small mammals that suffered major population declines associated with a wildfire in south‐eastern Australia. The observed ecological and genetic patterns during population recovery were inconsistent with simulation predictions from models of recovery by immigration from outside the fire‐affected area, but consistent with nucleated recovery from local fine‐scale refuges for one species (the bush rat) and with a model of in situ recovery within burnt forest for another species (the agile antechinus, Antechinus agilis ).…”