The feeding ecology of the northern hairy-nosed wombat, Lasiorhinus krefftii (Marsupialia: Vombatidae)

Woolnough, Andrew Paul (1998) The feeding ecology of the northern hairy-nosed wombat, Lasiorhinus krefftii (Marsupialia: Vombatidae). PhD thesis, James Cook University.

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The northern hairy-nosed (NHN) wombat, Lasiorhinus krefftii, is critically endangered. It is restricted to a single population at Epping Forest National Park (EFNP) in semi-arid central Queensland. Apart from critically endangered status, the NHN wombat is unique among the larger grazing mammals because of its semi-fossorial lifestyle. This study investigated the feeding ecology of the NHN wombat, a key component in understanding the ecology of this species.

Epping Forest National Park is a tropical savanna. The burrows of the NHN wombat are associated with alluvial sands of a ancient streambed and an open eucalypt woodland. The rainfall at EFNP is seasonal but irregular, and the study was conducted in four years of below average rainfall. The seasonal trends in rainfall result in variation in the quality and quantity of forage available to the NHN wombat.

Fundamental to this thesis was measurement of temporal variability in the forage available to the NHN wombat. Forage quantity was monitored by the BOTANAL technique, allowing quantification of forage attributes including species composition, biomass and ground cover. In addition, primary productivity was monitored during the same period. Forage quality was measured by Near Infra-red Spectrometry (NIRS), calibrated to standard laboratory procedures. This technique allowed precise and reliable measurements of attributes of forage quality. These attributes included total nitrogen concentration, concentration of fibre (neutral detergent fibre, acid detergent fibre and acid-lignin), concentration of carbohydrates (water soluble carbohydrates), in vitro dry-matter digestibility (IVDMD) and organic matter content.

The biomass and species composition of forage available to the NHN wombat was dominated by the introduced grass Cenchrus ciliaris (83.1 ± 6.4% of the total biomass). Of the native grasses, Enneapogon spp., Aristida spp. and Chrysopogon fallax dominated the biomass and species composition. In addition, the sedge Fimbristylis dichotoma occurred frequently, despite contributing little to the overall biomass. The diversity of forbs at EFNP was high, dominated by Waltheria indica, Salsola kalii and species of the Malvaceae. However, forbs represented only a minor component of the biomass and total species composition. Overall the biomass of the forage available to the NHN wombat was high, above 1000 kg.ha⁻¹ (dry matter) year round. Primary productivity was positively correlated with rainfall.

The quality of forage species showed considerable temporal variation, with total nitrogen concentration in particular having a positive correlation with rainfall. Generally, the nutritional quality of the forage was poor, with seasonal variability in the concentration of nitrogen (range 0.3 to 2.5% of dry matter), concentration of fibre (range for neutral detergent fibre 54.9 to 86.8% of dry matter) and IVDMD (range 22.6 to 57.7% of dry matter). How the NHN wombat responded to such poor quality forage, both behaviourally and physiologically, was investigated.

Estimating the species composition of the diet of the NHN wombat is a key issue in an understanding of its feeding ecology. However, techniques used to describe the diets of herbivores have often been questioned for their precision. Consequently three methods were used to estimate the composition of the diet of the NHN wombat: stable carbon isotope analysis, conventional histological analysis and long-chain alkane analysis. Stable carbon isotope analysis partitioned the diet into plants consumed that had a C₃ photosynthetic pathway (essentially forbs) or a C₄ photosynthetic pathway (tropical grasses). Using faecal samples and hair samples (representative of assimilated carbon incorporated into body tissue), it was determined that the diet of the NHN wombat consisted primarily of tropical grasses, but this approach could not describe the botanical composition of the diet.

Analysis of epidermal residues and the concentration of long-chain alkanes in faeces were used to estimate the species composition of the diet. Conventional histological techniques compare the cell patterns of epidermal fragments in the faeces with a reference collection of epidermal patterns of plants available to the herbivore. Long-chain alkane analysis, however, takes advantage of the relatively indigestible wax component of the epidermis of plants consumed by the herbivore. One of the chemical components of the epidermal wax is long-chain alkanes (C₂₅ to C₃₆), each plant species with its own unique signature of alkanes. By comparing the patterns of long-chain alkanes in the faeces with a reference collection of plants available to the herbivore, through a least-squares optimisation procedure, an estimate of the composition of the diet could be generated.

The diet of the NHN wombat was dominated by Aristida spp. (20.6 ± 6.0% of epidermal residues), Enneapogon spp. (17.2 ± 6.3% of epidermal residues) and C. ciliaris (14.5 ± 5.5% of epidermal residues), and to a lesser extent by W. indica (2.0 ± 2.0% of epidermal residues) and F. dichotoma (1.9 ± 1.6% of epidermal residues). Unidentifiable epidermal fragments were the largest component of the diet determined by the histological technique (40.4 ± 13.2% of epidermal residues). The NHN wombat exhibited little temporal variation in the plants it consumes, suggesting it is a generalist in its forage choice. However, both the histological technique and the long-chain alkane analysis have limitations. Despite these limitations, the estimation of the diet of the NHN wombat in this study is the best possible with current methods.

Body composition of the NHN wombat was investigated by estimating levels of total body fat by Bioelectrical Impedance Analysis (BIA). The method of BIA was successfully calibrated on the southern hairy-nosed (SHN) wombat, Lasiorhinus latifrons, using stable isotopes of water and chemical analysis of the carcasses of SHN wombats. Multiple linear regression models using BIA plethysmograph measurements (resistance and impedance) and total body mass, were successful in predicting body fat (r² = 0.90, S.E. = 1.99) and total body water (r² = 0.90, S.E. = 1.64). Once calibrated, the BIA was applied to the NHN wombat.

The NHN wombat maintained a relatively constant level of total body fat (7.6 ± 3.5% of total body mass) despite seasonal variability in the quality of available forage. However, there was some evidence to suggest that altered states of body composition (e.g. the storage of body fat) may be of considerable importance to females during lactation.

The behaviour and activity of the NHN wombat were investigated by radio telemetry with data loggers incorporated into the collar packages. The three- channel data logger measured activity, intensity of light and temperature, with a recording schedule of one record from the three channels every 5 minutes and a data storage capacity of 1 Mb. The ranging behaviour of the NHN wombat was conservative, with core home-ranges averaging only 6.8 ± 3.8 ha (70% harmonic mean activity contour). Likewise, the activity of the NHN wombat was also conservative. The mean number of bouts of activity in a twenty-four hour period was just 25.2 ± 11.1 with each bout lasting on average 7.6 ± 2.2 minutes. Bouts of activity occur both above-ground and within the burrow, although the significance of activities within the burrow is unknown. When above-ground, the NHN wombat maintained low levels of activity, rarely undertaking behaviour that resulted in high measurements of activity. Above-ground activity was positively correlated with rainfall, and hence the quality and quantity of the forage. When rainfall was high, activity was low. However, the ambient temperature may also impose important limitations on the behaviour and activity of the NHN wombat.

The habitat of the NHN wombat was shared by the eastern grey kangaroo, Macropus giganteus. The female adult body size of the eastern grey kangaroo is equivalent to the female adult body size of the NHN wombat allowing a comparison of aspects of their feeding ecology. Both herbivores have a preference for grasses with the species composition of their diets overlapping by more than 90%. Unlike the NHN wombat, the eastern grey kangaroo is not reliant on burrows. Following rainfall, the eastern grey kangaroo population declines in response to more favourable forage conditions beyond the boundaries of EFNP. They then return to EFNP as the quality and quantity of forage on surrounding pastoral properties decline. Although the density of eastern grey kangaroos is generally low on EFNP (seasonal range of 0.4 ± 0.6 to 16.9 ± 12.3⁻²), the similarities in forage and habitat preference indicate that there is potential for competition of food resources.

In summary, the lifestyle of the NHN wombat is one of extreme energy conservation, through its relationship with burrows, conservative behaviour and high digestive efficiency. The NHN is able to cope with the seasonally fluctuating savanna of northern Australia. The drought conditions encountered during this study resulted in a forage resource that was generally poor in quality. Despite possible nutrition restrictions, the NHN wombat exhibited little variation in its body composition or body condition throughout the study period. Therefore, the NHN wombat should be regarded as an extraordinary herbivore, well-suited to its semi-arid habitat.

Item ID: 27494
Item Type: Thesis (PhD)
Keywords: northern hairy-nosed wombat; Lasiorhinus krefftii; forage quality; forage quantity; diet composition; forage choice; activity levels
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Woolnough, Andrew P., Foley, William J., Johnson, Christopher N., and Evans, Murray (1997) Evaluation of techniques for indirect measurement of body composition in a free-ranging large herbivore, the southern hairy-nosed wombat. Wildlife Research, 24 (6). pp. 649-660.

Date Deposited: 20 Jun 2013 01:23
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060201 Behavioural Ecology @ 70%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060303 Biological Adaptation @ 20%
06 BIOLOGICAL SCIENCES > 0606 Physiology > 060699 Physiology not elsewhere classified @ 10%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960899 Flora, Fauna and Biodiversity of Environments not elsewhere classified @ 30%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 70%
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