The roles of density dependence, developmental asynchrony, and niche traversal costs in shaping the evolution of ontogenetic complexity

James G DuBose

Most organisms undergo some degree of niche transition throughout their life cycles, which are typically accompanied by morphological, physiological, and/or behavioral changes. Ontogenetic complexity generally refers to the magnitude and abruptness of these changes. Evolutionary theory has described how various genetic properties facilitate and constrain the evolution of ontogenetic complexity, while ecological theory has described how ontogenetic dynamics shape populations and community dynamics. However, the general ecological properties that create a selective gradient for greater ontogenetic complexity have received less theoretical attention. To further our explanation of the evolution of ontogenetic complexity, here we present a general theoretical framework that considers the roles of population density, ontogenetic (a)synchrony, the breadth of competitive effects across niche space, and the costs of ontogenetic niche traversal in shaping the selective gradient for greater degrees of ontogenetic niche traversal. Mathematical analysis of this model showed that beyond a critical threshold, increasing population density monotonically increased the evolutionarily stable degree of ontogenetic niche traversal. However, this relationship was mediated by the degree of ontogenetic asynchrony and how diffuse competition was across niche space, both of which had non-monotonic effects on the evolutionarily stable degree of ontogenetic niche displacement. Density dependence is well established as a driver on life history evolution, and this framework further situates the evolution of ontogenetic complexity within the broader framework of life history evolution.