Do animal personalities promote species coexistence? A test with sympatric boreal rodents.

Abstract

The coexistence of competing species requires density feedbacks that have a larger effect on their own species' population growth than they do on others in the assembly. The feedbacks are often associated with behavioral tradeoffs that enable species to differentially exploit underlying axes of heterogeneity. Conjoining theories of species coexistence with foraging behavior and density-dependent habitat selection reveals that such tradeoffs impinge on invasion probabilities and equilibrium dynamics emerging from species' differences in habitat use. The resulting habitat separation promotes coexistence by reducing the overall interaction among species. Differential habitat selection depends on the behavioral abilities of organisms to identify and exploit the most profitable habitats and resource patches. One might thus expect that each species will evolve behavioral types distinct from those of other potential competitors. Accordingly, we exposed four coexisting species in four genera of boreal rodents to open-field tests. We used principal components (PC) to summarize their behaviors along three independent axes corresponding with clines of exploratory, vigilant, and apprehensive personalities. We confirmed that the axes represented repeatable behaviors (personalities) and assessed differences among species with a general linear model (GLM). The GLM revealed highly distinct differences among species, and between pairs of species, on each PC. Even so, it is difficult to infer the adaptive advantages of personality to the habitat segregation that reduces otherwise high interactions among species. Rather, personalities are best interpreted as co-adaptive behaviors reflecting the complex of morphological, physiological and behavioral attributes that dictate tradeoffs and enable coexistence.