Modeling applied to drifting in aquatic insects

다국어 초록 (Multilingual Abstract)

Stream and river habitats are characterized by a uni-directional water flow. Organisms colonizing such habitats are faced with the constraint of continuous downstream flow. Some ecologists find it puzzling that upstream is colonized by insect communities although the insects are continuously faced with downstream flow. The obvious solution to the puzzle is that there exist compensatory strategies, three of which have gained some notoriety in recent years: 1) diffusive random movement and density-dependent regulation of population size; 2) daily directed movement during larvae stage; 3) the compensation of larval drift by adult upstream flight. We have adapted an eco-evolutionary individual-based model (IBM) to accommodate typical life events of aquatic insects, such as birth, death, diffusion, and drifting. The probabilities of these events, which occur on the individual level, depend on both biological (e.g., local competition, upstream flight by adult insects) and environmental (e.g., unidirectional flow) constraints. The evolution of selected traits, namely, adapted water velocity, drifting time and distance, and upward flight distance, was investigated through simulation. We find that, while the three strategies are generally able to sustain upstream populations, the exact compensation of drift loss allowed by upstream flight makes the third strategy less “asteful” a population of upstream flight strategists to outcompete diffusive movement strategists. We also report branching of adapted traits in drifting during the course of evolution. Individuals with high current velocity preferences either spend short (several seconds) or long (an hour) duration in water flow, while the individuals with low current-velocity preference only spend middle range (half an hour) of duration in water flow.