Intraspecific Behavioral Variation Research Articles

Does intraspecific variation in Trissolcus japonicus affect its response to non-target hosts?

AbstractHost specificity is a key criterion for the implementation of any biological control program. In parasitoid wasps, host specificity is mediated by their response to chemical cues directly and indirectly associated with their hosts during foraging. Although intraspecific variation in foraging behaviour is documented, it is rarely integrated into risk assessment studies of potential biological control agents, as is the case for Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), an Asian egg parasitoid and biological control agent of the invasive Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). In the present study, we compared the behavioural response of T. japonicus females of an adventive line present in Switzerland and an Asian line (Beijing USDA), recently mass released in Italy, to cues of its target host H. halys and non-target host Pentatoma rufipes (L.) (Hemiptera: Pentatomidae). We observed minimal differences in host acceptance, exploitation and suitability in no-choice tests. In contrast, the behavioural response to host contact kairomones left on leaf substrates significantly differed between the two lines. While both lines preferred chemical footprints of H. halys in comparison to P. rufipes, females of the Beijing USDA line responded more strongly to host kairomones. The observed intraspecific variation in behavioural traits highlights the relevance of considering genetically distinct parasitoid lines and their host foraging behaviour in biological risk assessment studies. However, the implications of intraspecific variation in parasitoid foraging behaviour for biological control of a pest and non-target effects in the field remain challenging to predict.

Individual reflectance of solar radiation confers a thermoregulatory benefit to dimorphic males bees (Centris pallida) using distinct microclimates.

Incoming solar radiation (wavelengths 290-2500 nm) significantly affects an organism's thermal balance via radiative heat gain. Species adapted to different environments can differ in solar reflectance profiles. We hypothesized that conspecific individuals using thermally distinct microhabitats to engage in fitness-relevant behaviors would show intraspecific differences in reflectance: we predicted individuals that use hot microclimates (where radiative heat gain represents a greater thermoregulatory challenge) would be more reflective across the entire solar spectrum than those using cooler microclimates. Differences in near-infrared (NIR) reflectance (700-2500 nm) are strongly indicative of thermoregulatory adaptation as, unlike differences in visible reflectance (400-700 nm), they are not perceived by ecological or social partners. We tested these predictions in male Centris pallida (Hymenoptera: Apidae) bees from the Sonoran Desert. Male C. pallida use alternative reproductive tactics that are associated with distinct microclimates: Large-morph males, with paler visible coloration, behave in an extremely hot microclimate close to the ground, while small-morph males, with a dark brown dorsal coloration, frequently use cooler microclimates above the ground near vegetation. We found that large-morph males had higher reflectance of solar radiation (UV through NIR) resulting in lower solar absorption coefficients. This thermoregulatory adaptation was specific to the dorsal surface, and produced by differences in hair, not cuticle, characteristics. Our results showed that intraspecific variation in behavior, particular in relation to microclimate use, can generate unique thermal adaptations that changes the reflectance of shortwave radiation among individuals within the same population.

Exploratory behaviour divergence between surface populations, cave colonists and a cave population in the water louse, Asellus aquaticus

Behaviour is considered among the most important factors in colonising newhabitats. While population divergence in behaviour is well-documented, intraspecificvariation in exploratory behaviour in species with populations successfully colonising andadapting to extreme (compared to the ‘typical’) habitats is less understood. Here, by studyingsurface- vs. cave-adapted populations of water louse (Asellus aquaticus), we tested whether (i)adaptation to the special, ecologically isolated cave habitat includes a decrease inexplorativeness and (ii) recent, surface-type cave colonists are more explorative than theirsurface conspecifics from the source population. We repeatedly tested dispersal related novelarea exploration and dispersal speed in both the presence and absence of light. We found thatsurface populations showed higher behavioural activity in dark than in light, and they weremore explorative and dispersed faster than their cave conspecifics. Recent colonists showed atrend of higher dispersal speed compared to their source surface population. We suggest thatextreme and isolated habitats like caves might work as ‘dispersal traps’ following successfulcolonisation, because adaptation to these habitats includes the reduction of explorativeness.Furthermore, we suggest that individuals with higher explorativeness are likely tocolonise markedly new environments. Finally, we provide experimental evidence aboutsurface A. aquaticus moving more in dark than in light.Significance statementEnvironmental conditions in caves are differing drastically from those of the surface. Consequently, animals colonising subterranean habitats are subject to different selective forces than those experienced by the ancestral surface-living population. Behaviour is believed to be a key factor in successful colonisation to novel habitats; however, intraspecific behavioural variation in species with both surface- and cave-adapted populations is less known. Here, we compared dispersal related novel area exploration and dispersal speed across surface and cave-adapted populations of the freshwater crustacean Asellus aquaticus. Our results show that cave-adapted A. aquaticus are significantly less explorative and disperse slower than surface-type populations, indicating that caves may act as ‘dispersal traps’, where adaptation includes the loss of explorativeness. Also, recent cave colonists show a trend to be faster dispersers than peers from the surface source population, suggesting that individuals with higher explorativeness are likely to colonise markedly different new environments.

Neuroendocrine correlates of juvenile amphibian behaviors across a latitudinal cline

We assessed the macrogeographic and neuroendocrine correlates of behavioral variation exhibited by juveniles, an important life stage for dispersal, across the expansive range of the wood frog. By rearing animals from eggs in a common garden then using a novel environment test, we uniquely demonstrated differential expression of juvenile behaviors among 16 populations spanning 8° latitude. On the individual level, cluster analysis indicated three major behavior profiles and principal component analysis resolved four unique axes of behavior, including escape, foraging, food intake, feeding efficiency. We found that increased escape behavior was associated with lower adrenocorticotropic hormone (ACTH)-induced circulating corticosterone (CORT) levels, however, foraging and food intake behaviors were not associated with either resting or ACTH-induced CORT. At the population level, the expression of foraging behaviors increased with latitude while food intake behaviors declined with latitude, which raised several hypotheses of eco-evolutionary processes likely driving this variation. Given that these behaviors covary along the same ecological gradient as locally adapted developmental traits, genomic studies in this species could provide deep insights into how HPA/I activity is associated with the eco-evolutionary processes that structure intraspecific variation in morphology and behavior.

Among-individual variation in white seabream (Diplodus sargus) spatial behaviour and protection in a coastal no-take area

Abstract Marine protected areas (MPAs), and specially no-take areas (NTAs), play an important role in protecting target populations from fisheries. When developing spatial conservation and management tools, the design has mainly focused on population-level measures of fish home ranges, spawning and feeding areas, and migration routes. Intraspecific differences in fish behaviour, however, are often not accounted for, even though they could influence the level of realized protection. In this study, we investigated the intraspecific variation in spatial behaviour of a harvested fish, Diplodus sargus, and how it impacts the degree of protection granted by a NTA in the south of Portugal. We identified four behavioural types according to their spatial behaviour: residents, commuters, seasonal visitors, and single users. Time at risk (i.e. outside the NTA) greatly varied among the four groups, but also over the year for the seasonal and the single users. Our study shows how acoustic telemetry can assist spatial conservation and fisheries management and provides novel insight regarding the role of individual variation in behaviour to understand protection granted by MPAs to harvested species. It also suggests that incorporating such information into all stages of MPA design and implementation can result in increased resilience of the protected populations.

Geographic, climatic, and phylogenetic drivers of variation in colobine activity budgets.

Folivorous primates are typically considered time minimizers because the constraints of their unique digestive systems require them to spend a large portion of their activity budgets resting. However, inter- and intraspecific behavioral variation in their activity budgets may be influenced by local geographic and climatic conditions and evolutionary history. We compiled 48 studies representing ten genera, 31 species, and 50 populations to assess geographic (elevation, latitude), climatic (precipitation, temperature), and phylogenetic correlates of colobine activity budgets. Time spent resting negatively correlated with time spent feeding, moving, and socializing. Except for time spent socializing, activity budgets were independent of phylogeny, with more time spent feeding and less time resting in higher-elevation habitats and at lower temperatures. Among the four most common genera in our sample, only in Rhinopithecus did time spent feeding increase with higher elevations (range, 950-3950m above mean sea level) and lower temperatures (range, 0.9-25 ℃). Only in Trachypithecus did time spent resting decrease with lower temperatures (range, 19-25 ℃). Our findings suggest that there are no apparent effects of geographic or climatic gradients on colobine activity budgets except for Rhinopithecus and Trachypithecus, whose activities are biased in favor of energy maximization rather than time minimization. Compared with other colobines, the ability of Rhinopithecus to adapt their activity budget at high elevations may make them less vulnerable to climate change, while the greater sensitivity of Trachypithecus to heat may make them more vulnerable to climate change.

Small mammal personalities generate context dependence in the seed dispersal mutualism

Mutualisms are foundational components of ecosystems with the capacity to generate biodiversity through adaptation and coevolution and give rise to essential services such as pollination and seed dispersal. To understand how mutualistic interactions shape communities and ecosystems, we must identify the mechanisms that underlie their functioning. One mechanism that may drive mutualisms to vary in space and time is the unique behavioral types, or personalities, of the individuals involved. Here, our goal was to examine interindividual variation in the seed dispersal mutualism and identify the role that different personalities play. In a field experiment, we observed individual deer mice (Peromyscus maniculatus) with known personality traits predating and dispersing seeds in a natural environment and classified all observed interactions made by individuals as either positive or negative. We then scored mice on a continuum from antagonistic to mutualistic and found that within a population of scatter hoarders, some individuals are more mutualistic than others and that one factor driving this distinction is animal personality. Through this empirical work, we provide a conceptual advancement to the study of mutualism by integrating it with the study of intraspecific behavioral variation. These findings indicate that animal personality is a previously overlooked mechanism generating context dependence in plant–animal interactions and suggest that behavioral diversity may have important consequences for the functioning of mutualisms.

Leapfrog migration and residents: New migratory habits in Swedish Greylag geese.

Knowledge about intraspecific and individual variation in bird migration behavior is important to predict spatiotemporal distribution, patterns of phenology, breeding success, and interactions with the surrounding environment (e.g., human livelihoods). Such variation is key to adaptive, evolutionary responses, i.e., how individuals respond spatiotemporally to the environment to maximize fitness. In this study we used GPS location data from one to three full annual cycles from 76 Greylag geese (Anser anser) to test the hypothesis that geese originating at five latitudinally separated capture sites in Sweden have different migration strategies. We also assessed individual consistency in movement strategy over consecutive annual cycles. We used the scale‐independent net squared displacement modeling framework to quantify variables of autumn and spring migration for geese from each capture site: distance, timing, and duration. Our results demonstrate a positive correlation between migration distance and latitudinal origin. Geese from the northernmost site on average migrated farther south and about 15 times as far as the short‐moving or resident geese from the two southernmost sites. Movement strategies of individual geese varied considerably both within and among capture sites. Individual consistency in movement strategy from one annual cycle to the consecutive was high in geese from the northern sites moving the farthest, whereas the resident or short‐moving geese from the southernmost sites generally showed lower or no individual consistency. These changes have come about during a time span so short (i.e., ca. 35 years or 8–10 generations) that it can unlikely be explained by classical Darwinian between‐generation adaptation. Consequently, and given that young geese follow their parents during their first migration, we presume an important role of within‐family, inter‐generation change as a driver behind the large‐scale changed migration habits in Swedish Greylag geese.

Divergent predator activity muddies the dynamic landscape of fear

AbstractThe landscape of fear (LOF) hypothesis is a unifying idea explaining the effects of predators on the space use of their prey. However, empirical evidence for this hypothesis is mixed. Recent work suggests that the LOF is dynamic, depending on the daily activity of predators, which allows prey to utilize risky places during predator down times. While this notion clarifies some discrepancies between predictions and observations, support for a dynamic LOF remains mixed. The underlying assumption of a dynamic LOF is strong predictability in predator activity cycles. Work in multi‐predator systems demonstrates the effect of differential behavior between predator species on the predictions of prey space use. However, none have considered the effect of intraspecific variation in predator behavior. Most, if not all, dynamic LOF studies base inference on the species‐level average activity pattern, implicitly assuming similarity within the predator population. We examined the dynamics and intraspecific variation in activity cycles within a population of coyotes (Canis latrans). We found seasonality in the predictability of coyote behavior, as well as divergent nocturnal and crepuscular activity patterns between individuals during summer. Activity dynamics were not related to range size, sex, body mass, or habitat complexity, but did vary by year. These results suggest that the predictability of activity patterns is seasonally dynamic, and failure to account for intraspecific variation in activity may cloud inference in LOF studies. We argue that future studies should not neglect the potential complexity of predator behavior with simplistic assumptions. By considering intraspecific variation in activity patterns, we may gain a clear picture of LOF dynamics.

Modelling migration in birds: competition's role in maintaining individual variation.

Animals exhibit extensive intraspecific variation in behaviour. Causes of such variation are less well understood. Here, we ask when competition leads to the maintenance of multiple behavioural strategies. We model variability using the timing of bird migration as an example. Birds often vary in when they return from non-breeding grounds to establish breeding territories. We assume that early-arriving birds (counting permanent residents as 'earliest') select the best territories. But arriving before the optimal (frequency-independent) breeding date incurs a fitness penalty. Using simulations, we find stable sets of return dates. When year-round residency is viable, the greatest between-individual variation occurs when a small proportion of permanent residents is favoured, and the rest of the population varies in their return times. However, when fitness losses due to year-round residency exceed the benefits of breeding in the worst territory, all individuals migrate, although their return dates often vary continuously. In that case, individual variation is inversely related to fitness risks and positively related to territory inequality. This result is applicable across many systems: when there is more to gain through competition, or when its risks are small, a diversity of individual strategies prevails. Additionally, stability can depend upon the distribution of resources.

Intra-specific Variation in the Social Behavior of Barbary macaques (Macaca sylvanus).

Non-human primates show an impressive behavioral diversity, both across and within species. However, the factors explaining intra-specific behavioral variation across groups and individuals are yet understudied. Here, we aimed to assess how group size and living conditions (i.e., captive, semi-free-ranging, wild) are linked to behavioral variation in 5 groups of Barbary macaques (N=137 individuals). In each group, we collected observational data on the time individuals spent in social interactions and on the group dominance style, along with experimental data on social tolerance over food and neophobia. Our results showed that differences in group size predicted differences in the time spent in social interactions, with smaller groups spending a higher proportion of time in close spatial proximity, but a lower proportion of time grooming. Moreover, group size predicted variation in dominance style, with smaller groups being more despotic. Social tolerance was affected by both group size and living conditions, being higher in smaller groups and in groups living in less natural conditions. Finally, individual characteristics also explained variation in social tolerance and neophobia, with socially integrated individuals having higher access to food sources, and higher-ranking ones being more neophobic. Overall, our results support the view that intra-specific variation is a crucial aspect in primate social behavior and call for more comparative studies to better understand the sources of within-species variation.

Beneath the Leaf-Litter: Can Salamander Personality Influence Forest-Floor Dynamics?

Ecological research demonstrates how intraspecific phenotypic variation can have consequences for community dynamics. However, the effects of animal personalities (i.e., intraspecific behavioral variation) on ecological processes remains relatively understudied. Using Red-backed Salamanders (Plethodon cinereus) and the detrital food web as a model system, we conducted a laboratory mesocosm experiment to explore whether or not the personality type of a top-level predator could affect the community structure within a complex, terrestrial food web. We used behavioral assays to investigate the repeatability of salamander behaviors, and classified individuals as either active or inactive. We then subjected laboratory mesocosms to one of four treatments for 3 mo: one active salamander, one inactive salamander, control (no salamander), and a pre-experimental reference. Our results indicate that the effect of P. cinereus on the detrital food web might be behaviorally mediated, with only the most active salamanders affecting community structure. Specifically, mesocosms housing active salamanders contained less diverse invertebrate communities than all other treatments. This difference was primarily driven by springtails, which were more abundant within mesocosms housing active salamanders. We also found that salamander personality was associated with cover board use inside mesocosms, with inactive salamanders exhibiting a more philopatric use of cover objects than active individuals. Leaf-litter degradation did not differ between treatments, indicating that the ecological effects of salamanders were too weak to influence basal resources within the detrital food web. Our study prompts further questions regarding the potential for animal personalities to influence ecological processes within terrestrial communities.

A framework for studying behavioral evolution by reconstructing ancestral repertoires.

Although different animal species often exhibit extensive variation in many behaviors, typically scientists examine one or a small number of behaviors in any single study. Here, we propose a new framework to simultaneously study the evolution of many behaviors. We measured the behavioral repertoire of individuals from six species of fruit flies using unsupervised techniques and identified all stereotyped movements exhibited by each species. We then fit a Generalized Linear Mixed Model to estimate the intra- and inter-species behavioral covariances, and, by using the known phylogenetic relationships among species, we estimated the (unobserved) behaviors exhibited by ancestral species. We found that much of intra-specific behavioral variation has a similar covariance structure to previously described long-time scale variation in an individual's behavior, suggesting that much of the measured variation between individuals of a single species in our assay reflects differences in the status of neural networks, rather than genetic or developmental differences between individuals. We then propose a method to identify groups of behaviors that appear to have evolved in a correlated manner, illustrating how sets of behaviors, rather than individual behaviors, likely evolved. Our approach provides a new framework for identifying co-evolving behaviors and may provide new opportunities to study the mechanistic basis of behavioral evolution.

Intraspecific variation in longevity of Drosophila prolongata (Diptera: Drosophilidae) under solitary and group conditions

AbstractConsiderable variations in behavior and physiology exist among sexes and strains of species. The amount and allocation of energy resources can affect the health and survival of individuals. If an individual devotes a large amount of energy to interact with other conspecifics, the resources may become too scarce to maintain their physical condition, which could reduce longevity. In this study, I examined the interactive effects of sex, strain, and the presence of conspecifics on adult longevity using four strains of Drosophila prolongata. This species shows a large intraspecific variation in behavior and morphology among isofemale strains. Under solitary conditions, longevity was significantly different among strains for both sexes. The effects of same‐sex conspecifics on adult longevity were also highly variable between the sexes and among strains. When exposed to conspecifics, the longevity of males of a hyper‐aggressive strain was more notably decreased than that of females of the same strain or either sex of other less aggressive strains. These results indicate that differences in the balance of costs and benefits of social interactions lead to differences in adult longevity under group conditions between the sexes and among strains within the same species.

Testing the relationship between intraspecific competition and individual specialization across both behavior and diet.

Individual specialization within populations is increasingly recognized as important in both ecology and evolution, but researchers working on intraspecific variation in behavior and diet infrequently interact. This may be because individual specialization on diet and behavior was historically difficult to investigate simultaneously on the same individuals. However, approaches like stable isotope analysis that allow hindcasting past field diets for laboratory organisms may provide opportunities to unite these areas of inquiry. Here, we tested the role of intraspecific competition on individual specialization through analysis of both behavior and diet simultaneously. We focused on intraspecific competition as a mechanism that might drive individual specialization of both diet and behavior. We conducted this study in Vilas County, Wisconsin, United States (US), using rusty crayfish Faxonius rusticus from six lakes across a relative abundance gradient. We conducted six assays to measure individual specialization of behavior and used stable isotope analysis to measure individual specialization of diet. We then related both measures of individual specialization to relative abundance of F. rusticus using linear and quadratic models. We found a unimodal relationship between intraspecific competition and individual specialization of diet for F. rusticus, likely because some preferred resources are unavailable to specialize on at the highest densities of this well‐studied crayfish invader. Conversely, we found greater support for a linear relationship between individual specialization of behavior and intraspecific competition, perhaps because specialization by behavior is not inherently resource‐limited. Our results show that dietary and behavioral specialization may exhibit different responses to increased intraspecific competition, and demonstrate a potential technique that can be used to investigate individual specialization of diet and behavior simultaneously for the same individuals and populations.

Behavioral Variation in the Pygmy Halfbeak Dermogenys collettei: Comparing Shoals With Contrasting Ecologies

Variation in biotic and abiotic factors among populations affects individual behaviors by transforming the social landscape and shaping mating systems. Consequently, describing behaviors in natural populations requires consideration of the biological and physical factors that different individuals face. Here, we examined variation in socio-sexual and locomotor behaviors in a small, livebearing, freshwater fish, the pygmy halfbeak Dermogenys collettei, across natural populations in Singapore. The pygmy halfbeak is a surface feeding fish that spends most of the time near the water surface, making it ideal for non-invasive behavioral observations. We compared behaviors between sexes among 26 shoals while simultaneously accounting for environmental variation. We demonstrated that sexual interactions and locomotor behaviors differed among shoals with varying levels of canopy cover and water flow. Specifically, in areas with greater canopy cover, sexual interactions decreased, whereas time spent in a stationary position increased. Sexual interactions were more numerous in still water, where fish spent less time swimming. Variation in the expression of socio-sexual and locomotor behaviors were not associated with differences in the amount of aquatic vegetation, water depth or halfbeak shoal size. Agonistic interactions were robust to environmental effects, showing little variation among environments. However, there were strong sex effects, with males performing more agonistic behaviors and spending less time in a stationary position compared to females, regardless of the environment. Moreover, sexual interactions, measured as actively performed by males and passively received by females, were on average more frequent in males than in females. Our findings help us explore the proximal causes of intraspecific behavioral variation and suggest that fundamental information on socio-sexual behaviors from wild populations can lead to a better understanding of how sexual selection operates when the strength of natural selection varies across environments.

Prosociality, social tolerance and partner choice facilitate mutually beneficial cooperation in common marmosets, Callithrix jacchus

Prosocial motivation has been suggested to facilitate the initiation and maintenance of cooperative interactions, as well as the evolution of social systems reliant on helping behaviour and social coordination. Previous comparative research on the link between prosociality and cooperation has been limited, however, by the absence of directly comparable measures of these traits among the same individuals. In the present study, we therefore examined intraspecific variation in prosociality and cooperative behaviour within a captive colony of group-living, cooperatively breeding common marmosets to provide a direct experimental test of these hypothesized benefits. We measured prosociality using a group service food-provisioning paradigm, and we assessed mutually beneficial dyadic cooperation with the loose string coordinated pulling paradigm. In addition, we also investigated the effects of individual social tolerance and partner choice, which have previously been identified as key factors promoting prosociality and cooperation among primates. As predicted, successful cooperation in the loose string paradigm was positively associated with prosociality, as well as with social tolerance and partner choice. These effects were independent of age, sex, personality, food motivation and learning across experimental sessions. Our results therefore suggest that prosocial motivation, social tolerance and partner choice can each facilitate mutually beneficial cooperation and social coordination in marmosets, supporting the hypothesized role of these mechanisms in the evolution of cooperative behaviour among primates.

Individual consumer movement mediates food web coupling across a coastal ecosystem

AbstractThe movement and foraging patterns of consumers are a major driver of nutrient and energy distribution in ecosystems. However, relatively little is known about how intraspecific variation in consumer movement behavior might affect food web coupling and ecosystem processes across landscapes and seascapes. Here we use long‐term acoustic telemetry and stable isotope niche metrics to understand how differences in predatory fish movement patterns control food web coupling and resource subsidies across the Florida Coastal Everglades (USA). We found common snook (Centropomus undecimalis) that spent most of their time in freshwater riverine areas of the Shark River Estuary primarily foraged on prey subsidies originating from adjacent marsh habitats, serving as an important vector of nutrient subsidies to downstream habitats. Snook that spent the majority of their time in downstream estuarine habitats displayed a diversity of resource usage across wide spatial scales, occupied a much larger trophic niche, and serve as a multidirectional vector of trophic coupling among marine, estuarine, and freshwater riverine habitats. These results demonstrate how individual variations in predator movement behavior can mediate the direction and scale of food web subsidies across coastal seascapes.

Poor nutritional condition promotes high-risk behaviours: a systematic review and meta-analysis.

Animal behaviour can lead to varying levels of risk, and an individual's physical condition can alter the potential costs and benefits of undertaking risky behaviours. How risk-taking behaviour depends on condition is subject to contrasting hypotheses. The asset protection principle proposes that individuals in better condition should be more risk averse, as they have higher future reproductive potential (i.e. more to lose). The state-dependent safety hypothesis proposes that high-condition individuals that are more likely to survive and maximise the benefits of risky situations may make apparently riskier choices, as their individual risk is in fact lower. We systematically searched for studies that experimentally manipulated animals' nutritional or energetic condition through diet treatments, and subsequently measured risk-taking behaviour in contexts relating to predation, novelty and exploration. Our meta-analysis quantified condition effects on risk-taking behaviour at both the mean and variance level. We preregistered our methods and hypotheses prior to conducting the study. Phylogenetic multilevel meta-analysis revealed that the lower-nutritional-condition individuals showed on average ca. 26% greater tendency towards risk than high-condition individuals (95% confidence interval: 15-38%; N = 126 studies, 1297 effect sizes). Meta-regressions revealed several factors influencing the overall effect, such as the experimental context used to measure risk-taking behaviour, and the life stage when condition was manipulated. Meta-analysis of variance revealed no clear overall effect of condition on behavioural variance (on average ca. 3% decrease in variance in low- versus high-condition groups; 95% confidence interval: -8 to 3%; N = 119 studies, 1235 effect sizes), however, the experimental context was an important factor influencing the strength and direction of the variance effect. Our comprehensive systematic review and meta-analysis provide insights into the roles of state dependency and plasticity in intraspecific behavioural variation. While heterogeneity among effect sizes was high, our results show that poor nutritional state on average increases risk taking in ecological contexts involving predation, novelty and exploration.

Community context and dispersal stochasticity drive variation in spatial spread.

Dispersal is a key process in shaping species spatial distributions. Species interactions and variation in dispersal probabilities may jointly influence species spatial dynamics. However, many studies examine dispersal as a neutral process, independent of community context or intraspecific variation in dispersal behaviour. Here, we use controlled, replicated communities of two Tribolium species (T. castaneum and T. confusum) to examine how intraspecific variation in dispersal behaviour and community context influence dispersal dynamics in simple experimental landscapes composed of homogeneous habitat patches. We found considerable individual-level variation in dispersal probability that was unrelated to body size variation. Further, the context of dispersal mattered, as T. castaneum dispersal was reduced in two-species communities, while T. confusum dispersal was unaffected by community composition. Incorporating individual-level variation into a two-species stochastic spatial Ricker model, we provide evidence that individual-level variability in dispersal behaviour results in more variable spatial spread than assuming individuals have the same dispersal probability. Further, interspecific competition resulted in more variable spatial spread. The variability in spatial spread observed in our tightly controlled and replicated experimental system and in our stochastic model simulations points to potential fundamental limitations in forecasting species shifting ranges without considering potential interspecific interactions and demographic variability in dispersal behaviour.