A metabolic and body-size scaling framework for parasite within-host abundance, biomass, and energy flux

Energetics may provide a useful currency for studying the ecology of parasite assemblages within individual hosts. Parasite assemblages may also provide powerful models to study general principles of ecological energetics. Yet there has been little ecological research on parasite-host energetics, probably due to methodological difficulties. However, the scaling relationships of individual metabolic rate with body or cell-size and temperature may permit us to tackle the energetics of parasite assemblages in hosts. This paper offers the foundations and initial testing of a metabolic theory of ecology (MTE) framework for parasites in hosts. I first provide equations to estimate energetic flux through observed parasite assemblages. I then develop metabolic-scaling theory for parasite abundance, energetics, and biomass in individual hosts. In contrast to previous efforts, the theory factors in both host and parasite metabolic scaling, how parasites use host space, and whether energy or space dictates carrying capacity. Empirical tests indicate that host energetic flux can set parasite carrying capacity, which decreases as predicted considering the scaling of host and parasite metabolic rates. The theory and results also highlight that the phenomenon of “energetic equivalence” is not an assumption of MTE, but a possible outcome contingent on how species partition resources. Hence, applying MTE to parasites can lend mechanistic, quantitative, predictive insight into the nature of parasitism and can inform general ecological theory.

能量代谢可作为研究单个宿主体内寄生虫群落生态学的有效能量货币。寄生虫群落亦可作为研究生态能量学通用原理的优质模型体系。然而目前针对寄生虫-宿主生态能量学的研究仍较为匮乏，这大概率源于方法学上的难题。不过，个体代谢速率与体型、细胞大小及温度之间的异速缩放关系，为我们解析宿主体内寄生虫群落的生态能量学特征提供了可行路径。本文为宿主内寄生虫的生态能量学代谢理论（Metabolic Theory of Ecology, MTE）框架奠定了研究基础并完成了初步验证。本文首先推导了用于估算观测到的寄生虫群落能量通量的计算公式。随后，本文针对单个宿主体内的寄生虫丰度、能量代谢及生物量构建了代谢缩放理论。与既往研究不同，该理论同时纳入了宿主与寄生虫的代谢缩放关系、寄生虫对宿主空间的利用模式，以及究竟是能量还是空间决定种群容纳量这一核心议题。实证检验结果表明，宿主的能量通量可决定寄生虫的种群容纳量，且该容纳量会按照宿主与寄生虫代谢速率的缩放关系所预测的趋势下降。该理论与研究结果同时揭示，‘能量等价性’并非生态能量学代谢理论的预设前提，而是一种取决于物种资源分配方式的潜在结果。因此，将生态能量学代谢理论应用于寄生虫研究，可帮助我们从机制、定量与预测三个维度深入理解寄生现象的本质，同时也能为通用生态学理论的发展提供参考。