Date of Award
Thesis - ECU Access Only
Edith Cowan University
Master of Science (Biological Sciences)
School of Science
Translocations to closed systems such as fenced reserves are commonly used for the conservation of threatened fauna species worldwide and although fenced reserves can provide significant conservation benefits to biodiversity, they can also bring forth potential threats. Ecologically similar species can stably coexist by partitioning resources along at least one of three niche dimensions (food, space, or time), thereby reducing interspecific competition. However, resources are limited in fenced reserves and natural processes that regulate populations in response to resource availability, such as dispersal into surrounding areas, are unable to occur. Consequently, there is increased potential for competition because there are less resources available for partitioning. Furthermore, the removal of predators and competitors, both native and introduced, can increase the risk of overpopulation due to a reduction in the incidence of density-dependant mortality. This can potentially lead to overuse of resources and further increase the potential for competition. Interspecific competition may lead to the decline or exclusion of a more sensitive species by a less sensitive species. Such interactions are difficult to predict, especially as many threatened species no longer naturally co-exist in their current ranges or are poorly studied.
I investigated resource use of two potentially competing native marsupials, boodies (Bettongia lesueur) and mala (Lagorchestes hirsutus), that co-exist in a 1100 ha predator-free fenced reserve located in the arid rangelands of central Western Australia. Resource overlap between coexisting populations of these two species has not been studied previously, but the literature suggests the potential for considerable dietary overlap. I investigated the degree of dietary overlap using scat DNA from non-invasively collected scats, as well as the degree of spatial overlap using scat counts and temporal overlap using camera traps. Boom-bust dynamics have been observed in the Matuwa boodie population (and elsewhere), which raised the concern of subsequent suppression of the potentially less competitive mala. The suppression of mala however cannot be confirmed because there are currently no effective methods to monitor the population size of this elusive species at Matuwa. Therefore, I also trialled non-invasive DNA-based sampling methods using field-collected scats to estimate the abundance of the Matuwa mala population. This method has not been used on mala previously.
Results from the dietary analyses suggest there is potential for significant exploitative competition, as both species’ scats consisted of a high percentage of Acacia spp. However, the Acacia DNA could not be identified to species level and there are at least 19 Acacia species within the enclosure, so it is unknown which species they are consuming, and further studies are necessary to resolve the extend of overlap. Additionally, boodies also consumed a much higher proportion of fungi than mala, which may reduce the extent of overall dietary overlap, thereby reducing the potential for resource competition. The species displayed no sign of significant spatial or temporal avoidance at a broad scale, possibly because dietary partitioning exists so there is limited risk from using the same habitats and having similar activity rhythms. The results however, suggest the potential for fine scale spatial and temporal avoidance; this should be investigated further.
This study successfully used non-invasively collected scat DNA to identify individuals and estimate the abundance of the mala population at Matuwa. Spatially explicit capture recapture (SECR) and mark-resight models estimated a population size of over 110 individuals. With refined scat collection methods, DNA-based sampling will be an effective and valuable method for monitoring mala. This is a significant outcome because current methods have limited success with the elusive species, but it is essential the few remaining mala populations are effectively monitored to prevent further decline.
The information gained from this study will contribute to the successful conservation of boodies and mala by adding to existing knowledge and providing insight into the ability of these species to coexist. Finally, this study will contribute to gaining a better understanding of resource use by small mammals and how they partition resources (including food, space and time) in a closed environment where resources are significantly more limited than the wider landscape.
Treloar, S. (2022). Potential for resource competition between the boodie (Bettongia lesueur) and mala (Lagorchestes hirsutus) in the fenced Matuwa reserve, central Western Australia. Edith Cowan University. Retrieved from https://ro.ecu.edu.au/theses/2514