Decades of research have shown how perturbing a given trophic level can ripple through the chain causing a trophic cascade, which can have far-reaching consequences for ecosystem structure and functioning. Understanding the mechanisms behind trophic cascades has dominated big part of the food chain literature, mostly focused on the dynamical properties of ecosystems. Yet, food chains are not only defined by their dynamical properties but instead they are composed by an interconnected set of structural, functional and dynamical properties. Recent research has shown that the same physiological and environmental variables can determine both the strength of trophic cascades and the shape of structural properties, such as the biomass distribution across trophic levels. Here, we explicitly address the link between biomass distribution and the strength of trophic cascades. We provide a theoretical framework that relates both aspects of food chains and we test it with empirical data from 15 mesocosm experiments of pelagic communities.
Results/Conclusions
We found that more top-heavy communities (i.e., larger biomass at higher trophic levels) showed stronger bottom-up cascades, while more bottom-heavy communities had stronger top-down cascades. Importantly, our framework points at self-regulation (e.g, intra-guild predation) as a major determinant of the studied relationship. The framework presented allows to draw a direct link between the structural and dynamical properties of trophic communities and it provides a comprehensive understanding on the possible determinants of such a relationship, which is fundamental to predict and interpret the patterns observed in natural communities.