Moore Ben D, Foley William J
School of Botany and Zoology, Australian National University, Canberra ACT 0200, Australia.
Nature. 2005 May 26;435(7041):488-90. doi: 10.1038/nature03551.
Although defence against herbivores is often argued to be the main action of plant secondary metabolites (PSMs), very few examples have demonstrated that intraspecific variation in PSM concentrations influences foraging by wild vertebrate herbivores. Experiments with captive animals often indicate that PSM concentrations influence how much herbivores eat from individual plants, but these experiments do not replicate the subtle trade-offs in diet selection faced by wild animals, which must avoid predators and extremes of weather, interact with conspecifics, and achieve a balanced, nutritious diet, while avoiding intoxication by PSMs. We characterized the foliar chemistry of every tree from two Eucalyptus species available to a population of koalas (Phascolarctos cinereus) and considered rates of tree visitation over a ten-year period. We show that visitation rate was most strongly influenced by tree size, but that koalas also visited trees less frequently if the foliage contained either high concentrations of deterrent PSMs known as formylated phloroglucinol compounds, or low concentrations of nitrogen. Consequently, plant chemistry restricts the use of trees by this herbivore, and thus limits the food available to koalas and potentially influences koala populations.
尽管人们通常认为抵御食草动物是植物次生代谢产物（PSMs）的主要作用，但很少有实例表明PSM浓度的种内变异会影响野生脊椎动物食草动物的觅食行为。对圈养动物进行的实验常常表明，PSM浓度会影响食草动物从单株植物上摄取食物的量，但这些实验并未重现野生动物在饮食选择上面临的微妙权衡，野生动物必须躲避捕食者和极端天气、与同种动物互动，并获取均衡、营养丰富的饮食，同时避免被PSM毒害。我们对考拉（Phascolarctos cinereus）种群可获取的两种桉树种的每棵树的叶片化学成分进行了表征，并考虑了十年间的树木访问率。我们发现，访问率受树木大小的影响最大，但如果树叶中含有高浓度的被称为甲酰化间苯三酚化合物的抑制性PSM或低浓度的氮，考拉对树木的访问频率也会降低。因此，植物化学特性限制了这种食草动物对树木的利用，从而限制了考拉可获取的食物，并可能影响考拉种群。
