Animal Personality: Ecology, Behavior, and Evolution

The past decade has seen an extraordinary rise in the number of papers devoted to the study of consistent individual differences in behavior, termed variably as "personality", "behavioral types", "temperament", "correlated phenotypes", and/or "behavioral syndromes". In earnest, the acceleration of this field was initiated by a handful of reviews that focused on the ecological and evolutionary implications of personality, published in 2004(Dall et al., 2004; Sih et al., 2004a; Sih et al., 2004b). Although, the literature on animal personality had already experienced a rich history in the comparative psychology literature by this time (Gosling and John, 1999; Gosling, 2001). Earlier works by Felicity Huntingford (Huntingford, 1976) and Susan Riechert (Riechert and Hedrick, 1993; Riechert et al., 2001), along with more contemporary studies by Niels Dingemanse (Dingemanse et al., 2002; Dingemanse et al., 2003), had each hinted at the ecological significance of animal personalities for years. However, it was this synthesis of these case studies into a unified framework by Andy Sih and others that lead to the field's meteoric rise. The field of animal personality became enormously popular in the years following these early reviews. Hundreds of papers were published from countless study systems, e.g., birds , lizards (Cote et al., 2008; Carter et al., 2010), fish (Bell, 2005; Biro et al., 2010), squid (Sinn et al., 2008; Sinn et al., 2010), small mammals (Dochtermann and Jenkins, 2007), spiders (Johnson and Sih, 2005; Pruitt et al., 2008; Sweeney et al., 2013), crickets (Wilson et al., 2010). These studies tended to focus on documenting the presence of behavioral consistency and describing the correlations observed in behavioral measures across multiple ecological contexts. Traits like activity level, boldness, and aggressiveness were among the most commonly measured traits(Sih and Bell, 2008). However, at the same time as this rise in popularity, the field of animal personality was also bombarded with skepticism. In particular, many investigators questioned the true novelty of the animal personality movement, whether it would have tenure, and whether the animal personality perspective could be used profitably as an organization framework for the study of the long-standing goals/questions in behavior, ecology, and evolution. So, the field of animal personality deepened and diversified. Between the years of 2009 and 2014, dozens of reviews, ideas and perspectives pieces emerged (e.g., Cote et al., 2010; Stamps and Groothuis, 2010; Sih et al., 2012; Jandt et al., 2013). They considered various subsets of the emerging literature, and convincingly argued the potential implications of personality for fields ranging from behavioral genomics, to species interactions, invasion biology, sexual selection, epidemiology, and animal welfare, among others. These reviews, in turn, rapidly received dozens or hundreds of citations themselves and the number of plausible implications of animal personality grew to be truly overwhelming. Now, at least in my own view, the challenge for the field is to harness these ideas and test their utility in situ.