School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK.
J Theor Biol. 2012 May 7;300:368-75. doi: 10.1016/j.jtbi.2012.01.020. Epub 2012 Jan 24.
Many invertebrate herbivores sequester plant toxins from their food, and the availability of toxins and the costs and benefits of sequestering toxins may influence food patch choice. In many plants, young leaves contain higher concentrations of toxins than old leaves and so can be preferred by sequestering herbivores, even if herbivores are more readily detected by predators when on them. We modelled patch use and sequestration strategies for the growth period of herbivores, assuming that the effectiveness of a toxin against predators is positively related to its cost of sequestration and that high-reward patches have higher predation risk. We show that the empirically commonly-observed strategy of moving from a low-reward patch to a high-reward patch can be optimal in a range of circumstances, but especially those that are common in nature. Body size when herbivores are predicted to switch increases with increasing size of maturation under most conditions, whilst use of the high-reward patch increases. Our predictions about how the proportion of time spent in the high-reward patch changes with the distribution and potency of toxins indicate a reason for plant toxins to be relatively mild. We provide further testable predictions about the role of the plant's defence strategy and herbivore behaviour in tritrophic interactions.
许多无脊椎草食动物会从它们的食物中隔离植物毒素，而毒素的可用性以及隔离毒素的成本和收益可能会影响食物斑块的选择。在许多植物中，嫩叶比老叶含有更高浓度的毒素，因此即使草食动物在嫩叶上更容易被捕食者发现，它们也可能被隔离毒素的草食动物所偏好。我们为草食动物的生长时期建立了斑块利用和隔离策略模型，假设毒素对捕食者的有效性与隔离它的成本呈正相关，并且高回报斑块的捕食风险更高。我们表明，从低回报斑块转移到高回报斑块的经验上常见的策略在多种情况下可能是最优的，但在自然界中更常见的情况下尤其如此。在大多数情况下，当草食动物被预测要切换时，它们的体型会随着成熟度的增加而增加，而高回报斑块的利用率会增加。我们关于在高回报斑块中花费的时间比例如何随毒素的分布和效力而变化的预测，为植物毒素相对温和提供了一个原因。我们进一步提供了关于植物防御策略和草食动物行为在三营养级相互作用中的作用的可测试预测。
