Delayed chemical defense: timely expulsion of herbivores can reduce competition with neighboring plants

Time delays in plant responses to insect herbivory are thought to be the principal disadvantage of induced over constitutive defenses, suggesting that there should be strong selection for rapid responses. However, observed time delays between the onset of herbivory and defense induction vary considerably among plants. We postulate that strong competition with conspecifics is an important co-determinant of the cost-benefit balance for induced responses. There may be a benefit to the plant to delay mounting a full defense response until the herbivore larvae are mobile enough to leave, and large enough to cause severe damage to neighboring plants. Thus, delayed responses could reduce the competitive pressure on the focal plant. To explore this idea, we developed an individual-based model using data from wild tobacco, Nicotiana attenuata, and its specialized herbivore, Manduca sexta. Chemical defense was assumed to be costly in terms of reduced plant growth. We used a genetic algorithm with...植物应对昆虫植食的响应延迟，被认为是诱导型防御（induced defense）相较于组成型防御（constitutive defense）的主要劣势，这意味着快速响应会受到强烈的自然选择压力。然而，观测到的植食起始与防御诱导之间的时间延迟，在不同植物类群间差异显著。我们提出假说：与同种个体的强烈竞争，是影响诱导型防御响应成本-收益平衡的重要共同决定因素。植物延迟启动全面防御响应，直至植食性幼虫足够活跃可脱离寄主、且体型足够大到对邻近植株造成严重损害，可能对植株自身有利。因此，延迟的防御响应可降低目标植株所承受的竞争压力。为验证这一假说，我们基于野生烟草（Nicotiana attenuata）及其专性植食者烟草天蛾（Manduca sexta）的相关数据，构建了基于个体的模型（individual-based model）。研究假定化学防御会以植株生长受抑为代价。我们采用了遗传算法（genetic algorithm）以...