Conclusions
Life-history stages constitute part of biological diversity and increase complexity of food webs. As a large majority of organisms grow in size, often over orders of magnitude, during their lifetime and experience various degrees of ontogenetic diet shifts (Werner & Gilliam 1984), life-history structures are important to be considered in studies on the stability of complex food webs. In this study, we demonstrated a positive relationship between the complexity and stability of complex food webs; food webs with stage-structured taxa exhibited lower biomass variability and supported more taxa than did those with unlinked stages. These results are qualitatively in agreement with the findings by Mougi (2017). For aquatic systems and fishes in particular, ontogenetic stages are well recognized and studied so that including life-history stages explicitly in models can facilitate linking theory and data. Practically, including separate stages makes it more mechanistic and straightforward to implement allometrically scaled functions or parameters and differences in behaviors among stages. For example, simulating size-selective fishing and the evolutionary impacts of such fishing on the population dynamics of exploited species in food webs becomes more straightforward once a life-history structure is explicitly incorporated (e.g., Kuparinen et al. 2016). Moreover, our work contributes a way of incorporating another aspect of interaction diversity via life histories to the growing research on multi-layered networks . Biomass flow via growth and reproduction forms networks of energy transfer analogously to consumer-resource interactions. Research on multi-layered networks has so far revealed that non-trophic interactions (thus interaction diversity) can ameliorate or degrade the stability of trophic interactions and the persistence of species (reviewed by Kéfi et al. 2018). Interestingly, showed that network structures known to stabilize mutualistic interactions became less effective when combined with trophic interactions in a multi-layered network. Tritrophic food chain and omnivory modules have been shown to stabilize complex food webs (Stouffer & Bascompte 2010), and it will be instructive to examine if they still do so when embedded in complex food webs including ontogenetic biomass flow.