Copepod vertical distribution within a spatially variable food source: A simple foraging-strategy model

Abstract

An individual-based model of copepod behavioral responses to vertically patchy food was developed. It was hypothesized that a decrease in step length inversely proportional to the concentration of food (area-restricted search) would result in aggregation of the copepods within food patches, and a high value of food eaten/distance traveled. The performance of the copepods using the step-length reduction behavior was compared with two control behaviors. Copepods were allowed to forage through simulated distributions, and other distributions based on a high-resolution, field-sampled, vertical profile of fluorescence. The step-length reduction behavior led to higher values of food eaten/distance traveled, due to a significant portion (>30% at times) of the population that did extremely well compared with the others, in both the theoretical and real field-sampled distributions. The step-length reduction behavior also led to higher spatial correlation between the food and the copepods. This strategy should allow some copepods to bypass local food maxima, where they might not meet their daily feeding requirements and reach the area of highest food concentration within the water column. Copepods foraging within smoothed versions of the field profiles received little benefit from the step-length reduction behavior, emphasizing the importance of sampling the environment on the appropriate scale.