Behavioral and social mechanisms behind pattern formation: An experimental study of animal movement

Authors: CORDEIRO, ERICK M. - Kansas State University; Campbell, James - Jim; PHILLIPS, THOMAS - Kansas State University; WITH, KIMBERLY - Kansas State University

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2018
Publication Date: 11/1/2018
Citation: Cordeiro, E.G., Campbell, J.F., Phillips, T.W., With, K.A. 2018. Behavioral and social mechanisms behind pattern formation: An experimental study of animal movement. Ecology. 33(11):1881-1894. https://doi.org/10.1007/s10980-018-0713-1.
DOI: https://doi.org/10.1007/s10980-018-0713-1

Interpretive Summary: Newly harvested and stored grain is relatively homogenous, but when stored product insects colonize the grain they tend to not to be randomly distributed. How pattern of insect distribution in the grain develops is not well understood. Using an experimental model system in which the movement of lesser grain borer, Rhyzopertha dominica, a major pest of stored grain, was tracked in a single layer of wheat kernels, it was demonstrated that beetles were attracted to areas where they had previously fed, which over time lead to a more clumped distribution than predicted if they moved randomly. The sexes also differed in their movement with males when alone tending to move less and have less complex movement pathways than females, perhaps because males are known to release aggregation pheromone and females will be better able to locate source of pheromone if it is stationary. When a female beetle was in the presence of another female, movement increased but the two individuals kept a consistent distance from each other. When a male beetle was in the presence of a female, they moved further and had a more complex pathway, suggesting a switch to a more active search strategy that brings the male closer to female location. These two results suggest that females are detected in the grain mass, even though they are not reported to produce a pheromone. Our results provided insights into the mechanisms that generate non-random patterns of pest insect distribution in stored grain and indicate a previously unidentified chemical pheromone might play a role. Results will help in developing more effective monitoring programs and targeted pest management.

Technical Abstract: While animal movement and feeding behavior can be influenced by landscape heterogeneity, it can also create spatial heterogeneity in initially homogeneous landscapes through interactions with the landscape and other individuals. To examine the dual role that animal movement behavior can play in both creating and responding to spatial heterogeneity, we developed an experimental model system consisting of a homogeneous resource landscape of wheat kernels, and then evaluated how spatial pattern emerged within these landscapes by studying the movement and feeding of Rhyzopertha dominica, which is a seed predator and major pest of stored grain. Our findings reveal the existence of two, non-mutually exclusive sources of pattern formation in this system. First, beetles were significantly attracted to areas where they had previously fed, leading to a more patchy spatial distribution and increased heterogeneity. Second, beetle movement behavior was differentially influenced by the presence of conspecifics. Females exhibited greater daily net displacements when in the presence of another female compared to solitary females, but maintained a consistent distance from the other female. Solitary males had lower rates of movement and produced paths of lower complexity compared to solitary females. When paired with a female, however, males converged on female movements, increasing both their rate of movement and path complexity, which resulted in a more clumped distribution owing to the positive association between males and females. Our experimental model system thus provides insights into the mechanisms that underlie the reciprocal interaction between behavioral processes and pattern formation in homogeneous landscapes.