Amongst the many consequences of the anthropogenic-driven crisis is the emergence of novel communities with changed diversities, abundances and structures. In this context, while understanding the consequences of shifts in diversity and abundance have been widely recognized as a central issue over the last decades, interactions have received comparatively less attention. Yet, interactions disappear at a higher rate than species do and their impact on ecosystem functioning (EF) have been shown to be important. However, we do not fully understand how interactions influence EF in large realistic communities. By providing the underlying structure of communities and the paths of biomass through it, food webs provide an obvious and tractable framework to address this issue. Here we propose that the distribution of the different types of tri-trophic interactions (hereafter called motifs) provide an accurate predictor of ecosystem functioning in terms of biomass and productivity. Motifs indeed represent the different types of trophic interactions and thus different shapes of biomass transfers at a local scale. We applied a well-studied model of consumer-resource dynamic on both isolated motifs and empirical systems and tested (i) the influence of motifs distribution within empirical communities on ecosystem functioning and (ii) the correlation between the dynamic of isolated motifs and their influence on the overall functioning.
Results/Conclusions
The preliminary outputs of the model on isolated motifs revealed that even in simple small-scale networks, the structure of trophic interaction plays an important role in shaping biomass flows, consistent across simulation, metabolic types, allometric scaling and functional responses. Motifs indeed exhibit significantly different profiles of biomass allocation and fluxes among species. Yet, question still remains at this point to how this effect scale-up to the overall community as this will be the next step of our project. Previous study showed that communities' motifs profile is a generality of trophic networks and influences its stability. Over-represented motifs - such as omnivory and linear food chain - are indeed correlated to higher stability. Our findings will allow to deepen our understanding of the causes and consequences of the profile of over- and under-representation of motifs, in addition to contribute to building a framework for predicting changes in EF in a context of communities shift.