Poulin R
Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Oecologia. 1996 Mar;105(4):545-551. doi: 10.1007/BF00330018.
Within a host population, parasite infracommunities vary in both richness and species composition. If interspecific interactions among parasites are important in shaping infracommunities, the structure of these assemblages is expected to differ from the one predicted by null models, i.e. from the one that would result from chance alone. Using data from the literature, I tested for discrepancies between observed and random patterns in the richness and composition of gastrointestinal helminth infracommunities of birds and mammals. Both the Poisson distribution and a more sophisticated null model, derived from prevalence of the different parasite species in the host population, usually provided a good fit to the observed distributions of infracommunity richness among hosts. This suggests that parasite species do not co-occur more or less frequently than expected by chance. In mammals, the co-occurrence of all available parasite species in the same host individual, or maximum potential infracommunity richness, was less likely to be observed when several parasite species were available; this is also a phenomenon expected from the random assembly of parasite species. Finally, there was no evidence for a nested subset pattern among parasite species in a host population: rate species were distributed independently of common ones. The overall picture emerging from these results is one in which parasite assemblages are more likely to be the product of random events than of predictable and repeatable processes.
在宿主种群中，寄生虫群落内的丰富度和物种组成各不相同。如果寄生虫之间的种间相互作用对塑造群落内结构很重要，那么这些组合的结构预计会与零模型预测的不同，即与仅由随机因素导致的结构不同。利用文献中的数据，我测试了鸟类和哺乳动物胃肠道蠕虫群落内丰富度和组成的观察模式与随机模式之间的差异。泊松分布以及一个更复杂的零模型（该模型源自宿主种群中不同寄生虫物种的流行率）通常能很好地拟合宿主间群落内丰富度的观察分布。这表明寄生虫物种同时出现的频率并不比随机预期的更高或更低。在哺乳动物中，当有几种寄生虫物种存在时，同一宿主个体中所有可用寄生虫物种同时出现的情况，即最大潜在群落内丰富度，不太可能被观察到；这也是寄生虫物种随机组合所预期的一种现象。最后，没有证据表明宿主种群中的寄生虫物种之间存在嵌套子集模式：稀有物种的分布与常见物种无关。这些结果呈现出的总体情况是，寄生虫组合更有可能是随机事件的产物，而非可预测和可重复过程的产物。
