Top-down effects of intraspecific predator behavioral variation

Abstract

Abstract Among-individual variation in predator traits is ubiquitous in nature. However, the role of intraspecific trait variation in trophic dynamics has been seldom considered in community ecology. This has left unexplored a) to what degree does among-individual variation in predator traits regulate prey populations and b) to what degree do these effects vary spatially. We address these questions by examining how predator among-individual variation in functional traits shapes communities across habitats of varying structural complexity, in field conditions for the first time. We manipulated Chinese mantis (Tenodera sinensis) density and trait variability in experimental patches of old fields with varying habitat complexity and quantified the impacts on lower trophic levels, specifically prey and plant biomass. Our mantis groups thus contrasted in density (six or twelve individuals) and levels of variation in a key behavioral trait, activity level (movement on an open field). Our metric of habitat complexity was the density of plant material. In complex habitats and at high mantis densities, behaviorally variable groups decreased prey biomass by 35.1%, while at low densities, low levels of behavioral trait variability decreased arthropod biomass by 27.1%. Behavioral variability also changed prey community composition. Our results are among the first to demonstrate that among-individual trait variation can shape open species-rich prey communities. Moreover, these effects depend on both predator density and habitat complexity. Incorporating this important facet of ecological diversity revealed normally unnoticed effects of functional traits on the structure and function of food webs.