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Fundamental dietary specialisation explains differential use of resources within a koala population


The diets of individual animals within populations can differ, but few studies determine whether this is due to fundamental differences in preferences or capacities to eat specific foods, or to external influences such as dominance hierarchies or spatial variation in food availability. The distinction is important because different drivers of dietary specialisation are likely to have different impacts on the way in which animal populations respond to, for example, habitat modification. We used a captive feeding study to investigate the mechanisms driving individual dietary specialisation in a population of wild koalas (Phascolarctos cinereus) in which individuals predominantly ate either Eucalyptus viminalis or Eucalyptus obliqua foliage. All six koalas that primarily ate E. viminalis in the wild avoided eating E. obliqua for more than 1 month in captivity. In contrast, all seven koalas that primarily ate E. obliqua could be maintained exclusively on this species in captivity, although they ate less from individual trees with higher foliar concentrations of unsubstituted B-ring flavanones (UBFs). Our results show that fundamental differences between individual animals allow some to exploit food resources that are less suitable for others. This could reduce competition for food, increase habitat carrying capacity, and is also likely to buffer the population against extinction in the face of habitat modification. The occurrence of fundamental individual specialisation within animal populations could also affect the perceived conservation value of different habitats, translocation or reintroduction success, and population dynamics. It should therefore be further investigated in other mammalian herbivore species.

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We thank the Conservation Ecology Centre (Cape Otway) for their generous support of the project, and in particular for allowing us to use their facilities for housing koalas. Desley Whisson assisted with catching koalas, Jack Pascoe, Mark Le Pla and various interns at the Conservation Ecology Centre assisted with radio-tracking koalas, and Huiying Wu assisted with the care of captive koalas. The study was approved by the Australian National University Animal Experimentation Ethics Committee (protocol A2017/03), and was supported by a grant from the Australian Research Council to BDM and WJF (Linkage Programme LP140100751).

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All authors conceived and designed the experiments. KJM and MDJB performed the experiments. KJM and BDM analysed the data. KJM wrote the manuscript; other authors provided editorial advice.

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Correspondence to Karen J. Marsh.

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Communicated by Joanna E. Lambert.

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Marsh, K.J., Blyton, M.D.J., Foley, W.J. et al. Fundamental dietary specialisation explains differential use of resources within a koala population. Oecologia 196, 795–803 (2021).

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  • Herbivore
  • Dietary niche
  • Koala
  • Plant secondary metabolites
  • Unsubstituted B-ring flavanones