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A Comparative Dietary Analysis of the Black-flanked Rock-wallaby (Petrogale lateralis lateralis), Euro (Macropus robustus) and Feral Goat (Capra hircus) in Cape Range National Park, Exmouth, Western Australia.

Creese, Sonja (2007) A Comparative Dietary Analysis of the Black-flanked Rock-wallaby (Petrogale lateralis lateralis), Euro (Macropus robustus) and Feral Goat (Capra hircus) in Cape Range National Park, Exmouth, Western Australia. Honours thesis, Murdoch University.

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Abstract

Petrogale lateralis lateralis (Black-flanked Rock-wallaby) has declined in its mainland distribution to a few isolated populations with extant populations known from six localities in the Wheatbelt, the Cape Range, the Calvert Range, and Barrow and Salisbury Islands (Pearson and Kinnear 1997). The conservation status of P. l. lateralis is classified as endangered. It is therefore extremely important that the threatening processes associated with this species are investigated to ensure appropriate management of the remaining populations. P. l. lateralis is a herbivore with a foraging range restricted to rocky outcrops; competition for resources from introduced herbivores has been implicated as a limiting factor to rock-wallaby populations. The aim of this study was to examine possible dietary overlap between P. l. lateralis and two co-occurring species Macropus robustus (euro) and Capra hircus (feral goat) at Cape Range National Park in order to determine if there is competition for food resources. Vegetation surveys combined with dietary analysis of plant epidermal fragments found in the faecal material of the three species and direct behavioural and feeding observations were carried out at two study sites Mandu Mandu Gorge and Pilgonaman Gorge in Cape Range National Park, Exmouth, Western Australia. A seasonal comparison of the diets of P. l. lateralis, M robustus and C. hircus at the study sites was conducted to highlight the time of year that competition for food resources is most prevalent.

Vegetation profiles and the vegetation surveys conducted within the Mandu Mandu Gorge and Pilgonaman Gorge show that plant species vary in abundance and occur in different areas within the gorges. Vegetation surveys showed that the vegetation structure between Mandu Mandu Gorge and Pilgonaman Gorge differed but contained an overlap of plant species. Mandu Mandu Gorge consisted of mainly Triodia grasslands with Acacia sp. The vegetation in Pilgonaman Gorge becomes increasingly dense the farther east into the gorge with the dominant species Ipomoea costata and Ficus brachypoda with a variety of herb and grass species. Hence, the plant species that herbivores forage on in Mandu Mandu Gorge and Pilgonaman Gorge are limited spatially due to changes in vegetation structure within the gorges, with dense patches occurring on the gorge floor and scattered plants occurring around P. l. lateralis refuge sites and on the rocks of the gorge walls.

The faecal analysis found that approximately 60% of P. l. lateralis diet consisted of dicotyledon species in summer with consistently higher proportions, (approximately 70% dicotyledons) in winter. The species occurring in the highest proportions in the P. l. lateralis diet at Pilgonaman Gorge in summer were Ficus platypoda (12.5 %), Ptilotus obovatus (11.5%) and Ipomoea costata (7.5%) F. platypoda comprised of (17.6%), I. costata (10.6%), P. obovatus (11.5%) and Plumbago zeylanica comprised (10.6%) of the diet in winter. The percentages of identified dicotyledon species in the summer diet at Mandu Mandu Gorge are as follows; F. brachypoda comprising of (15.7%), I. costata (11.8%), P. obovatus (11.8%), and Solanum sp. (2%) The main plant present in the P. l. lateralis diet in winter at Mandu Mandu Gorge was F. brachypoda (14.5%), followed by I. costata (13.3%), P. obovatus (7.2%), then Solanum sp. (3.6%), P. zeylanica (2.4%) and Achyranthes aspera (2.4%)

The proportion of monocotyledon and dicotyledon species for M robustus remained constant between both summer and winter in both gorges. There was little variation in the proportion of monocot species consumed between summer and winter in Mandu Mandu Gorge and Pilgonaman Gorge. Approximately 25 % of the diet consisted of dicotyledon species. M robustus consumed Myrtaceae sp., Sida sp. Ptilotus obovatus and Ipomoea costata in Pilgonaman Gorge in summer and Myrtaceae sp., Sida sp., P. obovatus and Ficus brachypoda in winter. In Mandu Mandu Gorge, M robustus consumed Myrtaceae sp., Sida sp. and P. obovatus in summer and Sida sp and P. obovatus in winter.

A high proportion of the C. hircus diet in this study consisted of dicot species. There was little variation in the percentage of dicot species consumed in summer and winter for C. hircus in both Mandu Mandu Gorge (63% in summer and 65% in winter) and Pilgonaman Gorge (67% in summer and 69% in winter). The identified dicot species in the C. hircus diet in the winter months at Pilgonaman Gorge comprised of I. costata (12.4%), P. zeylanica (9%), P. obovatus (9%), Sida sp. (5.6%), F. brachypoda 4.5%, Solanum sp. 3.3%, A. aspera (2.3%) and Myrtaceae sp. (1 %). The dicot species consumed by C. hircus at Mandu Mandu Gorge include Sida sp. (3.5 %), P. obovatus (17.5%), I. costata (8.8%), F. brachypoda (7%) and Solanum sp. (5.3%) of the summer diet. The winter diet for C. hircus at Mandu Mandu Gorge comprised of P. obovatus (15.1%), I. costata (8.1%) F. brachypoda (10.5%) and Solanum sp. (4.7%)

Direct observations of P. l. lateralis eating support the identification of plant species found within their faeces during the scat analysis of this study. Furthermore, physical evidence of grazing on leaves within Pilgonaman Gorge suggests that herbivores are actively grazing upon F. brachypoda, Malvaceae sp., Solanum sp., I. costata, Sida sp., P. zeylanica and Cenchrus ciliaris. P. l. lateralis, M robustus and C. hircus were found to consume a selection of these species in various proportions in the scat analysis.

A significant dietary overlap of plant species was found to occur between C. hircus, M robustus and P. l. lateralis in Pilgonaman Gorge and Mandu Mandu Gorge. P. l. lateralis, M robustus and C. hircus had a dietary overlap consuming the same plant species; Myrtaceae sp., Sida sp. C. ciliaris, I. costata and F. brachypoda and P. obovatus at differing percentages. C. hircus was found to forage on the following species in common with P. l. lateralis; Myrtaceae sp. Sida sp. C. ciliaris, I. costata and F. brachypoda, P. obovatus, Solanum sp., P. zeylanica and A. aspera. M robustus consumed Myrtaceae sp., Sida sp. C. ciliaris, I. costata and F. brachypoda, P. obovatus and E. caevuless in common with P. l. lateralis. The dietary overlap between C. hircus, M robustus and P. l. lateralis in Pilgonaman Gorge in summer was found to be significant with a probability of N= 22 W= 43.46 and P < 0.01. The dietary overlap between the species was consistent in winter N=22 and W= 41.02 and had the same probability value of P < 0.01. A significant dietary overlap occurred in summer with a probability of N=ll, W= 20.8 and P < 0.05 and winter N= 12, W= 24.25 and P < 0.02 in Mandu Mandu Gorge.

Finally, behavioural observations on interactions between feral goats and the rockwallabies indicate that when feral goats are at close range they are disruptive to the normal activities of rock-wallabies. This suggests that the goats are not only competing for food resources but that they may also elicit a form of interference competition. Implications of competition are discussed and recommendations for further research and management are considered.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Biological Sciences and Biotechnology
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor: Davies, Stephen and Bowen, Barbara
URI: http://researchrepository.murdoch.edu.au/id/eprint/40887
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