Most animals on the planet seem to exhibit some form of consistent individual variation in behavior. For instance, one goose might be exceptionally aggressive towards joggers its entire life, whereas another goose never harasses a jogger until the day it dies. These kinds of consistent patterns are called animal personality and they affect how individuals interact with members of their own species and other species. Aggressive water striders attack males and females so ferociously they prevent entire ponds of striders from mating. Active dragonfly larvae reduce the abundance of their prey, increasing the abundance of algae. Animal personality traits are thus functional traits with the potential to shape ecosystems. However, it remains unknown how animal personality affects complex ecosystems with numerous interacting populations. Here, I answer three key questions that reveal how and why animal personality shapes species interactions and ecosystem structure.
First, I asked whether the effect of animal personality on interactions between species depends on interactions between members of the same species. I tested whether behaviorally diverse katydids would be more likely to associate with members of their own species but reduce the survival of a potential competitor, froghoppers. Indeed, behaviorally diverse katydids tended to cluster together spatially and resulted in greater froghopper mortality. This suggests that the effect of animal personality on the interaction between these species may depend on how they interact with members of their own species.
Second, I asked whether habitat structure and predator cannibalism determine the effect of predator and prey personality on prey survival. We filled mesocosms with predators (mantis) and prey (katydid) groups and observed how their behavioral variability affected katydid survival, while half of the mesocosms were filled with additional habitat structure in the form of climbing sticks. Mantis behavioral diversity correlated with katydid survival, likely because diverse groups contained the fewest of highly lethal phenotype. However, this was only true when we added habitat structure. The effects of animal personality on interactions between these two species depend on the habitat structure available to them.
In ecosystems with hundreds of interacting species, the signal of individual behavioral traits from any one species could easily be lost. Third, I tested whether mantis behavioral diversity could affect the structure of wild ecosystems. I cut 4m2 squares into a meadow and added mantises with high and low levels of behavioral variability to the plots. After 40 days, I measured the biomass of plants and prey taxa in these plots. High mantis behaviorally diversity increased the biomass of the most dominant plant species (goldenrod), seemingly by reducing the prevalence of herbivores and predators. This demonstrates for the first time that animal personality can shape the structure of wild ecological communities.
Ecosystem processes occur at the scale of populations with numerous interacting species. These studies show how and why animal personality can affect species interactions and thereby ecosystems at a population level, whereas previous work focuses on the individual level. I thus show that animal personality can affect population-level processes in nature for the first time, opening the door to endless new questions.