Disturbance has benefits as well as costs for fragmented populations of a cryptic grassland reptile

Abstract

Context: Conservation practitioners face complex decisions about the management of spatial and temporal disturbance regimes when disturbance plays a significant role in the dynamics of fragmented populations. This is particularly so if disturbance events have negative short-term consequences but are necessary for maintaining habitat quality in the longer term. Objectives: We sought to determine the potentially interactive effects of two disturbance processes (fire and grazing) on the occupancy dynamics of the threatened Striped Legless Lizard (Delma impar) among native grassland fragments in Victoria, Australia. Methods: We collected 9 years of occupancy data from 291 sites. We used these data to examine the influence of disturbance frequency and coincidence on rates of occupancy and persistence, plus the influence of grassland connectivity on colonisation rates. Results: Fire and grazing were positively related to the persistence of D. impar populations at the frequencies observed during this study, but the interaction of these two disturbances had a strong negative effect on persistence. Colonisation of grassland fragments was positively related to connectivity to grassland habitat in the surrounding landscape. Conclusions: Strategic use of fire and grazing to manage fragmented grasslands can be beneficial for the persistence of D. impar populations, but intense and concurrent application of both these disturbances may trigger population collapse. Conservation risks of inappropriate disturbance are highest in small, isolated fragments of grassland, where recolonisation is unlikely. More broadly, our study highlights the value of coupling long-term occupancy and management data to investigate the influence of disturbance processes on population persistence in fragmented landscapes.