Spawton Kayla A, Wetzel William C
Department of Evolution & Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616.
Department of Evolution & Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616. Department of Entomology, Cornell University, Ithaca, NY 14853.
Environ Entomol. 2015 Aug;44(4):1095-100. doi: 10.1093/ee/nvv087. Epub 2015 Jun 17.
There is astounding variation in the abundance and diversity of insect herbivores among plant individuals within plant species in natural systems. One of the most well studied hypotheses for this pattern, the plant architecture hypothesis, suggests that insect community patterns vary with plant structural complexity and plant traits associated with structure. An important limitation to our understanding of the plant architecture hypothesis has been that most studies on the topic confound plant size and plant age. This occurs because, for most plant species, larger individuals are older individuals. This is a limitation because it prevents us from knowing whether insect community patterns are more dependent on traits associated with plant size, like resource quantity or plant apparency, or traits associated with plant age, like ontogenetic changes in phytochemistry. To separate these effects, we characterized galling insect communities on sagebrush (Artemisia tridentata)-a shrub in which age and size are not tightly correlated. We identified gall insects and recorded morphological measurements from 60 plants that varied separately in size and age. We found that plant size explained significantly more variation in insect gall abundance and species richness than did plant age. These results suggest that processes supporting the plant architecture hypothesis in this system are driven primarily by plant size and not plant age per se. Resource qualities associated with host-plant ontogeny may be less important than resource quantity in the assembly of herbivorous insect communities.
在自然系统中，植物物种内的不同植株个体间，植食性昆虫的数量和多样性存在惊人的差异。针对这种模式，研究最为充分的假说之一是植物结构假说，该假说认为昆虫群落模式会随植物结构复杂性以及与结构相关的植物性状而变化。我们理解植物结构假说的一个重要局限在于，该主题的大多数研究混淆了植株大小和植株年龄。出现这种情况是因为，对于大多数植物物种而言，较大的个体就是较老的个体。这是一个局限，因为它使我们无法知晓昆虫群落模式是更多地依赖于与植株大小相关的性状，比如资源数量或植物显眼程度，还是与植株年龄相关的性状，比如植物化学组成的个体发育变化。为了区分这些影响，我们对山艾树（三齿蒿）上的瘿蚊昆虫群落进行了特征描述，山艾树是一种年龄和大小并非紧密相关的灌木。我们识别了瘿蚊昆虫，并记录了60株在大小和年龄上分别有所不同的植株的形态测量数据。我们发现，相较于植株年龄，植株大小对昆虫瘿数量和物种丰富度变化的解释力要显著更强。这些结果表明，在这个系统中，支持植物结构假说的过程主要由植株大小驱动，而非植株年龄本身。在植食性昆虫群落的组成过程中，与寄主植物个体发育相关的资源质量可能不如资源数量重要。
