Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4295, USA.
Ecology. 2012 May;93(5):1026-35. doi: 10.1890/11-1320.1.
How insect herbivores affect plant performance is of central importance to basic and applied ecology. A full understanding of herbivore effects on plant performance requires understanding interactions (if any) of herbivore effects with plant density and size because these interactions will be critical for determining how herbivores influence plant population size. However, few studies have considered these interactions, particularly over a wide enough range of densities to detect nonlinear effects. Here we ask whether plant density and herbivores influence plant performance linearly or nonlinearly, how plant density affects herbivore damage, and how herbivores alter density dependence in transitions between plant size classes. In a large field experiment, we manipulated the density of the herbaceous perennial plant Solanum carolinense and herbivore presence in a fully crossed design. We measured plant size, sexual reproduction, and damage to plants in two consecutive years, and asexual reproduction of new stems in the second year, allowing us to characterize both plant performance and rates of transition between plant size classes across years. We found nonlinear effects of plant density on damage. Damage by herbivores and plant density both influenced sexual and asexual reproduction of S. carolinense; these effects were mostly mediated via effects on plant size. Importantly, we found that herbivores altered the pattern of linear density dependence in some transition rates (including survival and asexual reproduction) between plant size classes. These results suggest that understanding the ecological or evolutionary effects of herbivores on plant populations requires consideration of plant density and plant size, because feedbacks between density, herbivores, and plant size may complicate longer-term dynamics.
昆虫食草动物如何影响植物的表现，对基础和应用生态学具有核心重要性。要全面了解食草动物对植物表现的影响，就需要了解食草动物的影响与植物密度和大小之间的相互作用（如果有的话），因为这些相互作用对于确定食草动物如何影响植物种群的大小至关重要。然而，很少有研究考虑过这些相互作用，特别是在足够广泛的密度范围内，以检测非线性效应。在这里，我们询问植物密度和食草动物是否线性或非线性地影响植物表现，植物密度如何影响食草动物的伤害，以及食草动物如何改变植物大小类别的密度依赖性。在一个大型野外实验中，我们以完全交叉设计的方式操纵草本多年生植物 Solanum carolinense 的密度和食草动物的存在。我们在两年内测量了植物的大小、有性繁殖和植物的伤害，并在第二年测量了新茎的无性繁殖，这使我们能够描述植物表现以及植物大小类别的转变率在两年间的变化。我们发现植物密度对伤害有非线性影响。食草动物的伤害和植物密度都影响了 Solanum carolinense 的有性和无性繁殖；这些影响主要是通过对植物大小的影响来介导的。重要的是，我们发现食草动物改变了一些植物大小类别的线性密度依赖性的转变率（包括存活率和无性繁殖）的模式。这些结果表明，要理解食草动物对植物种群的生态或进化影响，需要考虑植物密度和植物大小，因为密度、食草动物和植物大小之间的反馈可能会使长期动态变得更加复杂。
