Cobb Neil S, Whitham Thomas G
Department of Biological Sciences, Northern Arizona University, 86011, Flagstaff, AZ, USA.
Oecologia. 1993 Jul;94(4):496-502. doi: 10.1007/BF00566964.
We examined the deme-formation hypothesis, which states that sessile herbivores on long-lived hosts become locally adapted to the defensive phenotypes of individual trees. We showed a five-fold increase in resistance by individual pinyon pines (Pinus edulis) to the pinyon pine needle scale (Matsucoccus acalyptus). Although such variation could represent a significant selection pressure favoring deme formation, two lines of evidence led to rejection of the hypothesis. First, there were no significant differences in mortality among scale populations in a reciprocal transfer experiment. Second, a seven-year experiment showed that mortality of newly founded, incipient scale populations was similar to established scale populations. While our experiments fail to support the deme-formation hypothesis, they do demonstrate significant variation in the resistance traits of a natural tree population. Although we feel that demeformation is still probable in this system, it is likely to occur on a larger geographic scale than individual trees as proposed by Edmunds and Alstad.
我们检验了种群形成假说，该假说认为，长期存在的宿主上的固着食草动物会在当地适应个体树木的防御表型。我们发现，单株矮松（Pinus edulis）对矮松针蚧（Matsucoccus acalyptus）的抗性增加了五倍。尽管这种变异可能代表了有利于种群形成的显著选择压力，但有两条证据导致该假说被否定。第一，在相互转移实验中，蚧虫种群之间的死亡率没有显著差异。第二，一项为期七年的实验表明，新建立的、初期的蚧虫种群的死亡率与已建立的蚧虫种群相似。虽然我们的实验未能支持种群形成假说，但它们确实证明了天然树木种群抗性特征的显著变异。尽管我们认为在这个系统中种群形成仍然是可能的，但它可能发生在比埃德蒙兹和阿尔斯塔德所提出的个体树木更大的地理尺度上。
