The ecology of the quokka (Setonix brachyurus) in the southern forests of Western Australia

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  • THESIS - DOCTOR OF PHILOSOPHY - BAIN Karlene Tracy - 2015

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  • Karlene Tracy Bain

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Abstract

Effective management of threatened species is dependent on knowledge of habitat, spatial requirements and threatening processes that affect populations, habitat quality, availability and connectivity. This knowledge is not available for all species and focal species whose ecological requirements encompass those of other species are often used as surrogates for management. Due to its large geographic range and sympatric association with a diverse range of endemic and threatened taxa, the quokka, Setonix brachyurus is such a species. It is a threatened species endemic to south-western Australia and is patchily distributed across a geographic range of approximately 18 000 km2. Ecological studies have been conducted for this species in the northern-most areas of its distribution on the mainland. The results of those studies have historically been used to guide management of habitat for the quokka in other parts of its distribution, despite observed differences in climate, population size, habitat characteristics and availability, and associated ecological communities. The goal of this study was to quantify a rapid survey technique, and to investigate habitat requirements, spatial ecology and response to fire for the quokka in the southern forests of south-western Australia in an effort to inform in situ conservation and guide future management of this species and others that share similar spatial, compositional, and functional requirements in this region.

A rapid survey technique based on counts of fresh faecal pellets was developed and evaluated against abundance estimates obtained from capture-mark-recapture (CMR)methods. Relative abundances obtained from faecal pellet counts were highly correlated with population estimates (R2 = 0.97) derived from more intensive CMR methods and provided a rapid and inexpensive survey option, where variation in detection probability was actively accounted for.

The features driving occupancy of habitat by quokkas in the southern forests were investigated. Quokkas in this region occupied habitats with complex vegetation structure, low densities of woody debris and fine scale habitat patchiness. Habitat features important to quokkas in the south were subtly different from those in the north where dense understorey and early seral stage vegetation were important. The subtle differences were found to be important and extrapolation of knowledge between these disconnected and ecologically diverse areas could result in inappropriate management and an increased risk of local extinction. Despite contiguous and extensive vegetation, significant segregation of subpopulations of quokkas was observed. Failure to consider anthropogenic processes that affect favoured habitat variables could contribute to increased habitat fragmentation resulting in intervening distances between habitat patches that are too great for successful dispersal, immigration and recolonisation processes.

Spatial use patterns and home range size of quokkas in the southern forests and the ability of individuals to move between segregated habitat patches was investigated using radiotelemetry. Quokkas in this region had much larger home ranges (mean 71.4 ha) and moved larger distances (up to 10 km per night) than previously reported for this species. Movement of quokkas between occupied habitat patches that were up to 14 km apart but connected by a linear riparian system was recorded. Emigrations across much larger distances are therefore possible, where habitats are suitably connected. A diverse range of habitats were used in addition to the riparian vegetation that has characteristically been considered primary habitat for this species. This has implications for the current approach to habitat protection, which focuses on protection of linear riparian systems. In particular, the broader habitat and spatial requirements for the species in this region are unlikely to be met by the current approach alone.

Fire has the potential to affect habitat connectivity and availability for the quokka in the southern forests. Factors driving the use of areas by quokkas following fire and the refuge value of unburnt vegetation were investigated. Retention of vertical vegetation structure, more than 20% of the area unburnt, and multiple unburnt pockets were important for quokkas to recolonise fire-affected areas rapidly. The application of fire to achieve these outcomes was dependent on relatively high surface and soil moisture and day of burn conditions that contributed to slow fire movement. Moisture differentials in riparian systems and discontinuous vegetation in rocky outcrops contributed to unburnt refugia under these conditions. Intense homogenising wildfire resulted in the complete loss of vertical vegetation structure, a lack of unburnt pockets and no re-colonisation of areas by quokkas for the duration of the study.

This study provides explicit ecological criteria to guide survey, management of habitat and fire planning in areas of the southern forest where quokkas are present. Use of such information will enable more effective management of critical habitat for this species and other taxa occupying a similar ecological niche.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Award date20 May 2016
StateUnpublished - 2015

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