Stalenberg Eleanor, Wallis Ian R, Cunningham Ross B, Allen Chris, Foley William J
Division of Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia.
Fenner School of Environment and Society, The Australian National University, Canberra, Australian Capital Territory, Australia.
PLoS One. 2014 Dec 3;9(12):e113930. doi: 10.1371/journal.pone.0113930. eCollection 2014.
It is widely postulated that nutritional factors drive bottom-up, resource-based patterns in herbivore ecology and distribution. There is, however, much controversy over the roles of different plant constituents and how these influence individual herbivores and herbivore populations. The density of koala (Phascolarctos cinereus) populations varies widely and many attribute population trends to variation in the nutritional quality of the eucalypt leaves of their diet, but there is little evidence to support this hypothesis. We used a nested design that involved sampling of trees at two spatial scales to investigate how leaf chemistry influences free-living koalas from a low-density population in south east New South Wales, Australia. Using koala faecal pellets as a proxy for koala visitation to trees, we found an interaction between toxins and nutrients in leaves at a small spatial scale, whereby koalas preferred trees with leaves of higher concentrations of available nitrogen but lower concentrations of sideroxylonals (secondary metabolites found exclusively in eucalypts) compared to neighbouring trees of the same species. We argue that taxonomic and phenotypic diversity is likely to be important when foraging in habitats of low nutritional quality in providing diet choice to tradeoff nutrients and toxins and minimise movement costs. Our findings suggest that immediate nutritional concerns are an important priority of folivores in low-quality habitats and imply that nutritional limitations play an important role in constraining folivore populations. We show that, with a careful experimental design, it is possible to make inferences about populations of herbivores that exist at extremely low densities and thus achieve a better understanding about how plant composition influences herbivore ecology and persistence.
人们普遍认为，营养因素驱动着食草动物生态学和分布中自下而上、基于资源的模式。然而，对于不同植物成分的作用以及它们如何影响个体食草动物和食草动物种群，存在很多争议。考拉（Phascolarctos cinereus）种群密度差异很大，许多人将种群趋势归因于它们所食用的桉树叶营养质量的变化，但几乎没有证据支持这一假设。我们采用了一种嵌套设计，涉及在两个空间尺度上对树木进行采样，以研究叶片化学如何影响来自澳大利亚新南威尔士州东南部低密度种群的自由生活考拉。我们以考拉粪便颗粒作为考拉对树木访问情况的替代指标，发现在小空间尺度上，叶片中的毒素和营养物质之间存在相互作用，与同一物种的相邻树木相比，考拉更喜欢叶片中有效氮浓度较高但铁氧体（仅在桉树叶中发现的次生代谢物）浓度较低的树木。我们认为，在低营养质量的栖息地觅食时，分类学和表型多样性可能很重要，因为它能提供饮食选择，以便在营养物质和毒素之间进行权衡，并将移动成本降至最低。我们的研究结果表明，在低质量栖息地中，直接的营养问题是食叶动物的一个重要优先事项，这意味着营养限制在限制食叶动物种群方面起着重要作用。我们表明，通过精心的实验设计，可以推断出极低密度存在的食草动物种群，从而更好地理解植物组成如何影响食草动物生态学和生存。
