Data from: The scaling of parasite biomass with host biomass in lake ecosystems: are parasites limited by host resources?

The standing crop biomass of different populations or trophic levels reflects patterns of energy flow through an ecosystem. The contribution of parasites to total biomass is often considered negligible; recent evidence suggests otherwise, although it comes from a narrow range of natural systems. Quantifying how local parasite biomass, whether that of a single species or an assemblage of species sharing the same host, varies across localities with host population biomass, is critical to determine what constrains parasite populations. We use an extensive dataset on all free-living and parasitic metazoan species from multiple sites in New Zealand lakes to measure parasite biomass and test how it covaries with host biomass. In all lakes, trematodes had the highest combined biomass among parasite taxa, ranging from about 0.01 to 0.25 g m-2, surpassing the biomass of minor free-living taxa. Unlike findings from other studies, the life stage contributing the most to total trematode biomass was the metacercarial stage in the second intermediate host, and not sporocysts or rediae within snail first intermediate hosts, possibly due to low prevalence and small snail sizes. For populations of single parasite species, we found no relationship between host and parasite biomass for either juvenile or adult nematodes. In contrast, all life stages of trematodes had local biomasses that correlated positively with those of their hosts. For assemblages of parasite species sharing the same host, we found strong relationships between local host population biomass and the total biomass of parasites supported. In these host–parasite biomass relationships, the scaling factor (slope in log-log space) suggests that parasites may not be making full use of available host resources. Host populations appear capable of supporting a little more parasite biomass, and may be open to expansion of existing parasites or invasion by new ones.

不同种群或营养级的现存量生物量（standing crop biomass）可反映生态系统的能量流动模式。寄生虫对总生物量的贡献常被认为可忽略不计；尽管现有相关证据仅来自有限的自然生态系统类型，但最新研究表明这一观点并不成立。量化局部寄生虫生物量——无论是单一物种还是共享同一宿主的物种集合——随宿主种群生物量在不同地点的变化规律，是明确制约寄生虫种群增长因素的关键所在。本研究依托覆盖新西兰多个湖泊站点的大型数据集，涵盖所有自由生活与寄生性后生动物（metazoan）物种，以此测定寄生虫生物量并检验其与宿主生物量的协变关系。在所有调查湖泊中，吸虫类（trematodes）在寄生虫类群中总生物量最高，范围约为0.01至0.25克每平方米，高于小型自由生活类群的生物量。与其他研究的结论不同，对吸虫总生物量贡献最大的生活史阶段是第二中间宿主体内的囊蚴（metacercarial stage），而非第一中间宿主螺类体内的胞蚴（sporocysts）或雷蚴（rediae），这一现象可能与螺类的感染率较低且体型较小有关。对于单一寄生虫物种种群，无论是幼年期还是成年期的线虫（nematodes），均未发现宿主与寄生虫生物量之间存在关联。与之相反，所有生活史阶段的吸虫局部生物量均与宿主生物量呈显著正相关。对于共享同一宿主的寄生虫物种种群集合，我们发现局部宿主种群生物量与其所支撑的寄生虫总生物量之间存在极强的关联。在这些宿主-寄生虫生物量关系中，标度因子（双对数空间中的斜率）表明寄生虫可能并未充分利用宿主可提供的资源。宿主种群似乎能够支撑略多的寄生虫生物量，也可为现有寄生虫种群的扩张或新寄生虫的入侵提供机会。