Models of pace-of-life syndromes (POLS): a systematic review

Variation in life history (LH) traits along the fast-slow continuum (referred to as pace of life, POL) is thought to result from a trade-off between investments in current versus future reproduction. Originally developed for understanding variation in LH strategies at the among-population level, the POL theory has more recently been applied towards understanding variation in LH traits at the within-population level, and further extended to address the covariance of LH traits with additional behavioural and/or physiological traits, referred to as pace-of-life syndromes (POLS). The article by Réale et al. (Philos T Roy Soc B 365:4051–4063, 2010), which synthesized several earlier reviews and opinions on among-individual covariation between LH, behavioural, and physiological traits, and subsequent research testing POLS in a variety of species, have collectively been cited several hundreds of times—a trend that continues. These works have interdisciplinary impact, informing research in life history biology, behavioural and developmental biology, and the social sciences. In this paper, we review the existing theoretical POLS models that provide adaptive explanations for covariances between LH traits and additional behavioural and/or physiological traits while assuming a trade-off between current and future reproduction. We find that the set of relevant models is small. Moreover, models show that covariances between life history traits and behavioural or physiological traits can arise even in the absence of a current-future reproduction trade-off, implying that observing such covariances does not provide a strong indication regarding the process generating POLS. We discuss lessons learned from existing models of POLS, highlight key gaps in the modelling literature, and provide guidelines for better integration between theory and data

Models of pace-of-life syndromes (POLS): a systematic review

Variation in life history (LH) traits along the fast-slow continuum (referred to as pace of life, POL) is thought to result from a trade-off between investments in current versus future reproduction. Originally developed for understanding variation in LH strategies at the among-population level, the POL theory has more recently been applied towards understanding variation in LH traits at the within-population level, and further extended to address the covariance of LH traits with additional behavioural and/or physiological traits, referred to as pace-of-life syndromes (POLS). The article by Réale et al. (Philos T Roy Soc B 365:4051–4063, 2010), which synthesized several earlier reviews and opinions on among-individual covariation between LH, behavioural, and physiological traits, and subsequent research testing POLS in a variety of species, have collectively been cited several hundreds of times—a trend that continues. These works have interdisciplinary impact, informing research in life history biology, behavioural and developmental biology, and the social sciences. In this paper, we review the existing theoretical POLS models that provide adaptive explanations for covariances between LH traits and additional behavioural and/or physiological traits while assuming a trade-off between current and future reproduction. We find that the set of relevant models is small. Moreover, models show that covariances between life history traits and behavioural or physiological traits can arise even in the absence of a current-future reproduction trade-off, implying that observing such covariances does not provide a strong indication regarding the process generating POLS. We discuss lessons learned from existing models of POLS, highlight key gaps in the modelling literature, and provide guidelines for better integration between theory and data

Models of pace-of-life syndromes (POLS): A systematic review

Variation in life history (LH) traits along the fast-slow continuum (referred to as pace of life, POL) is thought to result from a trade-off between investments in current versus future reproduction. Originally developed for understanding variation in LH strategies at the among-population level, the POL theory has more recently been applied towards understanding variation in LH traits at the within-population level, and further extended to address the covariance of LH traits with additional behavioural and/or physiological traits, referred to as pace-of-life syndromes (POLS). The article by Réale et al. (Philos T Roy Soc B 365:4051-4063, 2010), which synthesized several earlier reviews and opinions on among-individual covariation between LH, behavioural, and physiological traits, and subsequent research testing POLS in a variety of species, have collectively been cited several hundreds of times - a trend that continues. These works have interdisciplinary impact, informing research in life history biology, behavioural and developmental biology, and the social sciences. In this paper, we review the existing theoretical POLS models that provide adaptive explanations for covariances between LH traits and additional behavioural and/or physiological traits while assuming a trade-off between current and future reproduction. We find that the set of relevant models is small. Moreover, models show that covariances between life history traits and behavioural or physiological traits can arise even in the absence of a current-future reproduction trade-off, implying that observing such covariances does not provide a strong indication regarding the process generating POLS. We discuss lessons learned from existing models of POLS, highlight key gaps in the modelling literature, and provide guidelines for better integration between theory and data

Shorebirds as integrators and indicators of mudflat ecology

Shorebirds are major, but thus far under-acknowledged, players in mudflatfood webs and associated physio-chemical processes. Mud is a critical habitat type for shorebirds, offering a multi-dimensional matrix of feeding opportunitiesthrough space and time. Shorebirds have evolved a spectrum of foraging modes withassociated morphologies, and sensory and physiological adaptations which exploitthese foraging opportunities. Although shorebirds are mud specialists and sentinelsof mudflat ecosystem functioning, they have not yet been well integrated into the“mud club”. In this chapter, we highlight the key roles shorebirds play in food webs,and in physical and chemical processes within mudflat ecosystems. We illustratehow shorebird distribution and behaviour provides a mirror of mudflat ecologybecause their foraging behaviour reflects the underlying ecological conditions,including temporal and spatial patterns in food/community structure in and acrossmud. In particular, shorebirds may be important indicators of essential fatty acidproduction by diatoms in epibenthic biofilm fields covering muddy intertidal flats,especially in estuaries. We conclude by highlighting the major challenges facingshorebirds today and call for a paradigm shift in shorebird conservation, based onrecreating and restoring intertidal mud ecosystems

Animal personality and state–behaviour feedbacks: a review and guide for empiricists

An exciting area in behavioural ecology focuses on understanding why animals exhibit consistent among-individual differences in behaviour (animal personalities). Animal personality has been proposed to emerge as an adaptation to individual differences in state variables, leading to the question of why individuals differ consistently in state. Recent theory emphasizes the role that positive feedbacks between state and behaviour can play in producing consistent among-individual covariance between state and behaviour, hence state-dependent personality. We review the role of feedbacks in recent models of adaptive personalities, and provide guidelines for empirical testing of model assumptions and predictions. We discuss the importance of the mediating effects of ecology on these feedbacks, and provide a roadmap for including state–behaviour feedbacks in behavioural ecology research

Within-individual canalization contributes to age-related increases in trait repeatability: a longitudinal experiment in red knots

Age-related increases in the repeatable expression of labile phenotypic traits are often assumedto arise from an increase in among-individual variance due to differences in developmentalplasticity or by means of state-behavior feedbacks. However, age-related increases inrepeatability could also arise from a decrease in within-individual variance as a result ofstabilizing trait expression, i.e. canalization. Here we describe age-related changes in withinandamong-individual variance components in two correlated traits, gizzard mass andexploration behavior, in a medium-sized shorebird, the red knot (Calidris canutus). Increasedrepeatability of gizzard mass came about due to an increase in among-individual variance,unrelated to differences in developmental plasticity, together with decreases in withinindividualvariance, consistent with canalization. We also found canalization of exploration, butno age-related increase in overall repeatability, which suggests that showing predictableexpression of exploration behavior may be advantageous from a very young age onward.Contrasts between juveniles and adults in the first year after their capture provide support forthe idea that environmental conditions play a key role in generating among-individual variationin both gizzard mass and exploration behavior. Our study shows that stabilization of traitsoccurs under constant conditions: with increased exposure to predictable cues, individuals maybecome more certain in their assessment of the environment allowing traits to becomecanalized

Evolutionary design of a flexible, seasonally migratory, avian phenotype: why trade gizzard mass against pectoral muscle mass?

Migratory birds undergo impressive body remodelling over the course of an annual cycle. Prior to long-distance flights, red knots (Calidris canutus islandica) reduce gizzard mass while increasing body mass and pectoral muscle mass. Although body mass and pectoral muscle mass are functionally linked via their joint effects on flight performance, gizzard and pectoral muscle mass are thought to be independently regulated. Current hypotheses for observed negative within-individual covariation between gizzard and pectoral muscle mass in free-living knots are based on a common factor (e.g. migration) simultaneously affecting both traits, and/or protein limitation forcing allocation decisions. We used diet manipulations to generate within-individual variation in gizzard mass and test for independence between gizzard and pectoral muscle mass within individuals outside the period of migration and under conditions of high protein availability. Contrary to our prediction, we observed a negative within-individual covariation between gizzard and pectoral muscle mass. We discuss this result as a potential outcome of an evolved mechanism underlying body remodelling associated with migration. Although our proposed mechanism requires empirical testing, this study echoes earlier calls for greater integration of studies of function and mechanism, and in particular, the need for more explicit consideration of the evolution of mechanisms underlying phenotypic design

An experimental test of state–behaviour feedbacks: gizzard mass and foraging behaviour in red knots

1. Animals frequently exhibit consistent among-individual differences in behavioural and physiologicaltraits that are inherently flexible. Why should individuals differ consistently in theirexpression of labile traits? Recently, positive feedbacks between state and behaviour have beenproposed as a possible explanation for the maintenance of consistent among-individual differencesin both state and behaviour. If state affects behaviour, and behaviour reciprocally affectsstate, then differences in either state or behaviour that arise among individuals even by chancecould be maintained over extended periods of time.2. We tested for positive feedbacks experimentally using wild-caught red knots (Calidris canutusislandica). In the wild, knots exhibit consistent among-individual differences in digestivephysiology (the mass of the muscular part of the stomach, the gizzard) and foraging behaviour(diet), two inherently labile traits.3. Experimentally manipulated diet quality had a large effect on gizzard mass. Experimentallymanipulated gizzard mass reciprocally influenced total food eaten during ad libitum trials.4. The effect of gizzard mass on diet choice, though in the predicted direction, was not statisticallysignificant. Individuals exhibited consistent differences in foraging behaviour of unknownorigin independent of current gizzard mass, as well as large residual unexplained variance inforaging behaviour. These two sources of variation in foraging behaviour overruled the gizzardmass-dependent foraging behaviour and hence eroded the treatment-related differences in gizzardmass.5. We conclude that positive feedbacks between diet choice and gizzard mass play at best alimited role in maintaining among-individual variation in gizzard mass in red knots. Furthermore,we suggest that many models of state–behaviour feedbacks likely overestimate theirpotential importance in maintaining long-term among-individual variation in labile traitsbecause most models of state–behaviour feedbacks fail to account for the effects of additionalfactors that may act to disrupt the feedback loops.6. The among-individual differences in diet choice observed during solitary foraging trialseroded the consistent among-individual differences in gizzard mass observed following periodsof staple diet treatments in which knots foraged in social groups. Social foraging interactionsmay play an important role determining the expression of foraging behaviours such as intakerate that in turn influence gizzard mass. Further studies are needed to experimentally test therole of social interactions as a mechanism generating consistent among-individual differencesin foraging behaviours and gizzard mass