Foliar concentration of a single toxin creates habitat patchiness for a marsupial folivore

We examined intraspecific variation in susceptibility to herbivory by commo n ringtail possums (Pserrdocheirus peregrinus) for two species of Eucalyptu s, (E. polyanthemos and E. sideraxylon) and the chemical basis for that var iation. Using a no-choice protocol, we observed dry matter intakes by commo n ringtail possums ranging from 3.28 to 44 g.(kg body mass)(-0.75).d(-1) fo r E. polyanthemos and from 2.4 to 67 g(kg body mass)-0.75 d(-1) for E. side roxylon. We investigated, using correlative analyses, the relationships bet ween dry matter intake and a range of foliage chemical characteristics, inc luding measures of nutritional quality (total nitrogen, cellulose, hemi-cel lulose, lignin, in vitro dry matter digestibility) and plant secondary chem istry (total phenolics, condensed tannins, cyanogenic glycosides, terpenes, and sideroxylonal, a recently identified Eucalyptus toxin). Significant re lationships were identified only for terpenes (and 1,8-cineole in particula r) and sideroxylonal. Bioassay experiments confirmed that the foliar concen tration of sideroxylonal alone was sufficient to explain the variation obse rved. To undertake a field study of variation in foliar sideroxylonal and d ry matter intake by possums of E. polyanthemos, we developed calibrations o f both variables against the near infrared spectra of foliage samples. Acce ptable calibration equations were developed, and we applied these to sample s collected from a number of E. polyanthemos individuals within an area app roximating the home range size of common ringtail possums. We found that fo liar sideroxylonal varied from nil to 12.6 mg/g, while predicted dry matter intakes by possums ranged from nil to 42.8 g (kg body mass)(-0.75.d-1), We conclude that significant patchiness in nutritional quality of foliage, re sulting from variation in foliar concentrations of a single compound, exist s at a scale relevant to the feeding decisions of individual animals.