Shallow lakes, the most abundant freshwater ecosystems on earth, are characterized by the spatially asymmetric distribution of energy resources between pelagic and benthic habitats including nutrient and light. Fish, as a key factor providing pathways for energy and material transmissions between habitats, can significantly affect ecosystem functioning and lake stability. However, the influence of fish ontogeny, a ubiquitous phenomenon in nature, on the benthic-pelagic coupling has been largely overlooked. Here, to simulate how fish ontogeny mediated benthic-pelagic coupling affects shallow lake dynamics, we proposed a process-based and empirically well-fed shallow lake model where pelagic and benthic food chains are integrated by size-structured fish. Results show that species coexistence region is considerably enlarged in our model compared to the model counterpart without fish ontogeny,  suggesting that fish ontogenetic development improves ecosystem capacity to withstand harsh environment. Fish ontogeny is additionally demonstrated to act in concert with spatially asymmetric resource competition to regulate community biomass patterns, including algae bloom, by alleviating top-down control. Most importantly, our model shows that lake dynamics losses its stability when fish alter their living habitat from benthic to pelagic owing to light insufficiency or nutrient inadequacy/enrichment. The potential mechanism underlying such stability change is the energy leap induced by size-dependent habitat shifts. We conclude that the uncovered mechanism may become a general driver in undermining lake stability due to the ubiquity of fish ontogeny in natural ecosystems. Our results highlight the necessity to consider fish ontogenetic development in addition to spatial asymmetry of resource competition, when studying shallow lake responses to widespread environmental changes.
 

shallow lakes; spatial asymmetry; fish ontogeny; size structure; community structure; ecosystem stability