Dietary selectivity in the green ringtail possum Pseudochirops archeri: the effect of plant secondary metabolites on food preference

Jones, Katherine M.W. (2006) Dietary selectivity in the green ringtail possum Pseudochirops archeri: the effect of plant secondary metabolites on food preference. PhD thesis, James Cook University.

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Abstract

The feeding ecology of the green ringtail possum, Pseudochirops archeri was studied from 2003 to 2006 in a tropical rainforest fragment on the Atherton Tablelands, north Queensland. I investigated dietary preference at the level of tree species and individual trees within preferred species, the techniques for determining diet, the nutritional characteristics that were determinants of preference, and the use of a rapid, non-destructive technique for determining nutritional characteristics of rainforest foliage.

Three diet-determination techniques were tested. Faecal analysis, direct observation and tree-use each provided an indication of dietary preferences of P. archeri. Tree-use was selected as the most robust technique because preference could be statistically tested against availability of tree species at the site, it was the most time efficient method, and it provided information on individual tree use.

Green ringtail possums are highly specialised folivores, focussing foraging effort on only a few of the available trees at the site. Although there were 94 plant species identified in the canopy, over 50% of tree use was from only four tree species, Aleurites rockinghamensis, Ficus fraseri, Arytera divaricata and F. copiosa. These species were used significantly more frequently than would be expected if tree species were selected randomly in proportion to their relative abundance in the forest. Because there were few other social or behavioural reasons clearly contributing to preferential use of these species, I infer that they made up the majority of the diet. This was also supported by direct observation and faecal analysis. Possums also favoured particular individual trees within some of the preferred tree species, behaviour that has been well established in Eucalyptus-specialised folivores. In 91% of feeding observations, possums consumed mature leaves only. The availability of young leaves, flowers and fruit varied throughout the year, with a peak in availability of these resources during the early wet season. By primarily selecting mature leaves, green ringtail possums reduced their dependence on seasonally variable resources. I propose that this high degree of dietary specialisation might be due to advantages associated with limiting the number of plant secondary metabolites (PSM) in the diet and only secondarily minimising PSM intake within those species.

Near infrared reflectance spectroscopy (NIRS) was investigated as a potential tool for studying nutritional and defensive characteristics of rainforest leaves. Calibration equations developed in this study were successful in predicting chemical characteristics of rainforest leaves. NIRS is a particularly useful technique as once calibration equations are developed using samples of known composition, very large numbers of samples can be processed quickly and no chemical waste is produced. With further development, this technique has the potential to predict dietary intake by rainforest folivores and be used for broad-scale surveys of chemical characteristics of rainforest foliage.

Leaves from preferred and avoided plant species were tested for nitrogen concentration, digestible nitrogen concentration, nitrogen digestibility, dry matter digestibility, water content and cyanogenic glycoside concentration. Within the four preferred tree species, two different nutritional characteristics were associated with variation in individual tree use. Cyanogenic glycosides acted as a deterrent within the predominant preferred species, A . rockinghamensis, and within the remaining preferred species, F. fraseri, F . copiosa and A. divaricata, preference was positively related to nitrogen digestibility, but not gross nitrogen content, indicating an effect of nitrogendigestibility reducing tannins. The preference for mature leaves over juvenile was explicable by the same factors determining tree preference, as juvenile leaves were either higher in cyanogenic potential or lower in nitrogen digestibility. Tree species preference was not related to the same factors that determined preference within species. It is likely that interspecific selectivity is driven by a complex interaction between distribution and abundance of trees, as well as nutrients and PSMs, including compounds that were not measured in this study, and each non-preferred tree species may be avoided due to a different undesirable combination of these factors. Interspecific choice may be based on the need to minimise the diversity of PSMs ingested, whereas intraspecific choice may be based on the need to minimise the quantities of those few PSMs.

Item ID: 34854
Item Type: Thesis (PhD)
Keywords: behavioral ecology; behavioural ecology; diet; ecology; feeding ecology; feeding; foliovores; green ringtail possum; herbivores; nutrition; plant secondary metabolism; plant secondary metabolites; Pseudochirops archeri; PSM
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Jones, Katherine M.W., and Krockenberger, Andrew K. (2007) Determining the diet of cryptic folivores: an assessment of diet analysis techniques using the green ringtail possum (Pseudochirops archeri) as a case study. Wildlife Research, 34 (5). pp. 352-358.

Chapter 3: Jones, Katherine M.W., Maclagan, Sarah J., and Krockenberger, Andrew K. (2006) Diet selection in the green ringtail possum (Pseudochirops archeri): a specialist folivore in a diverse forest. Austral Ecology, 31 (7). pp. 799-807.

Date Deposited: 05 Sep 2014 06:40
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060201 Behavioural Ecology @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060208 Terrestrial Ecology @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 100%
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