REVIEW AND SYNTHESES Ecological implications of behavioural syndromes Andrew Sih, 1 * Julien Cote, 2  Mara Evans, 3 Sean Fogarty 4 and Jonathan Pruitt 5à Abstract Interspecific trait variation has long served as a conceptual foundation for our understanding of ecological patterns and dynamics. In particular, ecologists recognise the important role that animal behaviour plays in shaping ecological processes. An emerging area of interest in animal behaviour, the study of behavioural syndromes (animal personalities) considers how limited behavioural plasticity, as well as behavioural correlations affects an individualÕs fitness in diverse ecological contexts. In this article we explore how insights from the concept and study of behavioural syndromes provide fresh understanding of major issues in population ecology. We identify several general mechanisms for how population ecology phenomena can be influenced by a species or populationÕs average behavioural type, by within-species variation in behavioural type, or by behavioural correlations across time or across ecological contexts. We note, in particular, the importance of behavioural type-dependent dispersal in spatial ecology. We then review recent literature and provide new syntheses for how these general mechanisms produce novel insights on five major issues in population ecology: (1) limits to speciesÕ distribution and abundance; (2) species interactions; (3) population dynamics; (4) relative responses to human-induced rapid environmental change; and (5) ecological invasions. Keywords Animal personalities, behavioural syndromes, dispersal, distribution and abundance, ecological invasions, environmental change, intraspecific variation, population dynamics, spatial ecology, species interactions. Ecology Letters (2012) INTRODUCTION & GOALS Ecology has a long history of incorporating animal behaviour into analyses of ecological patterns and dynamics (Sutherland 1996; Fryxell & Lundberg 1998). Over the years, numerous articles have used optimality theory to explain forager diets, habitat use and predator avoidance that underlie predator-prey and competitive interactions that, in turn, potentially explain major patterns in population and community ecology (Valdovinos et al. 2010). A theme of this work is that classic issues like predator impacts on prey, competitive coexistence, or trophic cascades can often only be understood fully if we account for the behaviours of key species (Schmitz et al. 2008). Recent articles further emphasise behaviourÕs role in applied ecological issues like ecological invasions or relative species abilities to cope with human-induced rapid environmental change (Sih et al. 2011). Herein, we focus on ecological insights that come from the new emphasis in animal behaviour on behavioural syndromes (a.k.a. animal personalities) that acknowledges that in many species, individuals exhibit both within-individual and between-individual consistency in behaviours across time or across ecological contexts (Sih et al. 2004; Dall et al. 2004; Sih & Bell 2008). In many species, some individuals are consistently the more aggressive behavioural type (BT), whereas others are consistently less aggressive not just in competitive contests that involve aggression, but also in foraging, mating, parental and ⁄ or antipredator behaviour (Riechert & Hedrick 1993). Other documented BT axes include variation in boldness (Wilson et al. 1994) or sociability (Cote et al. 2010a). Although it has long been clear that humans differ in personality, and that a few other animals (e.g. primates, dogs, cats, laboratory rodents) exhibit consistent individual BTs, recent work suggests that behavioural syndromes apply across the entire animal kingdom (Gosling 2001). Behavioural syndromes are ecologically important because an individualÕs BT can clearly affect its fitness (Smith & Blumstein 2008; Biro & Stamps 2008). When different BTs are favoured in different environments, the existence of BTs can result in suboptimal behaviour in some environments. For example, individuals with a bold BT often take unnecessary risks and suffer high mortality in dangerous 1 Department of Environmental Science and Policy, University of California at Davis, 95616, USA 2 Department of Environmental Science and Policy, University of California at Davis, 95616, USA 3 Department of Evolution & Ecology, University of California at Davis, 95616, USA 4 Department of Environmental Science and Policy, University of California at Davis, 95616, USA 5 Department of Environmental Science and Policy, University of California at Davis, 95616, USA *Correspondence: E-mail: asih@ucdavis.edu   Current address: CNRS, EDB (Laboratoire Evolution et Diversite ´ Biologique), UMR 5174, Toulouse, France, and Universite ´ de Toulouse UPS, Laboratoire Evolution et Diversite ´ Biologique, 118 Route de Narbonne, Ba ˆ t. 4R3, 31062 Toulouse Cedex 9, France, julien.cote@cict.fr à Current address: Department of Biological Sciences, 213 Clapp Hall, University of Pittsburgh, Pittsburgh, PA 15260, USA, agelenopsis@gmail.com Ecology Letters, (2012) doi: 10.1111/j.1461-0248.2011.01731.x Ó 2012 Blackwell Publishing Ltd/CNRS