Matching behavior to the environment

Environmental changes affect animals’ survival, reproduction, and ultimately, fitness. The individualized niche framework posits that individuals within a population match their phenotype to the environment to increase fitness. Such phenotype-environment matching can be achieved through evolved individual-level processes such as environmental selection (i.e., niche choice) or phenotypic plasticity (i.e., niche conformance). Since animals typically first respond to environmental changes through their behavior, consistent among-individual differences in behavior, i.e., animal personalities, can importantly contribute to individualized niches. However, how individuals achieve a match between personality and the environment remains unexplored. This is a crucial avenue to explore since such individual-level processes can increase population mean fitness provided sufficient individuals use them. Personality traits often form suites of correlated behaviors (i.e., behavioral syndromes) that could restrict movement decisions. Individuals who are more risk-taking towards predators (boldness) are often more risk-taking towards conspecifics (aggressiveness). Further, personality traits like aggressiveness (and dominance rank) should determine outcomes of intraspecific competition. Such traits related to social aspects of behavior should be relevant under social contexts, e.g., aggressiveness should matter under different levels of intraspecific competition. Conversely, non-social traits should be relevant under specific environmental contexts, e.g., boldness should matter under various levels of predation risk. Thus, behavioral syndromes including both social and non-social traits likely affect movement decisions in environments that vary in both social and environmental factors. Yet, such behavioral syndromes remain poorly understood. Dispersal is fundamental to population dynamics and distribution, and is, thus, key to understanding how animals track favorable environmental change. Dispersal often correlates with animal personalities, with dispersers typically being bolder, more explorative, active, and aggressive. However, current empirical research demonstrates contrasting findings. Theory predicts that behavioral phenotypes should disperse from different social and environmental conditions to match their behavioral phenotype to the habitat (i.e., matching habitat choice). Mechanistically, this is likely due to variations in phenotype-specific cost-benefits of dispersal in different contexts. In the wild, multiple social and environmental factors act concurrently. Yet, how multiple co-occurring factors affect personality-dependent dispersal remains largely unstudied. The main objective of this thesis is to assess how personality traits related to social and non-social aspects of behavior form behavioral syndromes, contribute to the process of individualized niches, and relate to dispersal under various social and environmental contexts. This main objective is assessed in three core chapters. In Chapter I, I assessed among-individual correlations between two non-social personality traits (boldness and exploration) correlated with two traits related to social behavior (aggressiveness and dominance-related behavior). By repeatedly assessing the behavior of bank voles (Myodes glareolus) in standardized assays under lab conditions, I found that explorative individuals were bolder, more aggressive, and had higher levels of dominance-related behavior than less explorative conspecifics. Thus, confirming the existence of a behavioral syndrome of intraspecific competitiveness. By joining social and non-social aspects of personality, the findings from this chapter contribute to the ecological validation of personality traits and further our understanding of the existence of behavioral syndromes in animal societies. In Chapter II, I assessed whether and how risk-taking behavior contributes to the process of achieving a phenotype-environment match, i.e., individualized niches. Individualized niches were assessed under natural conditions for wild populations of common voles (Microtus arvalis). By in situ reducing safe environments in parts of the landscape, I found that behaviorally phenotyped individuals moved to choose habitats of predation risk that matched their risk-taking behavior (boldness and exploration), rather than plastically changing their behavior. These findings support matching habitat choice as a niche-altering mechanism. Thus, with this chapter, I provide evidence for a previously only theorized process and increase our understanding of individualized niches predicted by personality. Finally, building on findings from Chapters I and II, in Chapter III, I assessed whether and how personality traits covary with dispersal under different levels of predation risk and intraspecific competition. By assessing the dispersal propensity of behaviorally phenotyped bank voles under near-natural conditions outdoors, I found that the behavioral phenotype of dispersing individuals varied with both the environment of predation risk and intraspecific competition. Thus, demonstrating that individuals try to disperse from environments that do not match their behavioral phenotype of boldness, exploration, and dominance-related behavior. This chapter demonstrates that multiple social and environmental factors can concurrently affect covariance between dispersal and personality, and supports dispersal strategies as the process of inducing matching habitat choice. The three core chapters are framed by a general introduction and a general discussion. In the general introduction, I introduce core concepts and theory of among-individual differences in behavior and how they relate to niche theory and dispersal. In the general discussion, I synthesize the main findings in the core chapters, discuss potential outcomes, and identify future avenues of research. Importantly, this thesis tests, further develops, and bridges gaps between multiple theoretical frameworks and contrasting empirical patterns in research on personality-dependent dispersal. Consequently, providing valuable knowledge for understanding how individuals, and thus populations, may react to environmental changes.