Abstract
Species interactions characterize population dynamics and ecosystem
structure. While the population-level discussion is common in many
ecological studies, trait variations within a population and ontogenetic
diet/trophic niche shift are prevail across taxa. The ontogenetic
development may lead to an individual’s role shift, such as
inferior/superior competitor, prey, or predator. Here, we develop a
novel mathematical framework to bridge multiple levels of population
dynamics, such as trait, role, and population-level. We start with a
nonlinear trait-level model, and derive role-level and population-level
dynamics. By utilizing the connections, we demonstrate that the
population-level model predicts the equilibrium status of the role-level
model. In the role-level model, we discuss multiple role-shift
scenarios: from (i) inferior/superior competitor to superior/inferior
competitor, (ii) competitor to predator, and (iii) prey to predator. Our
approach connects traits, roles, and population dynamics consistently,
thus offering an opportunity to discuss the effect of species traits in
the population-level dynamics.