Theory predicts that high population density leads to more strongly connected spatial and social networks, but how local density drives individuals' positions within their networks is unclear. This gap reduces our ability to understand and predict density-dependent processes. Here we show that density drives greater network connectedness at the scale of individuals within wild animal populations. Across 36 datasets of spatial and social behaviour in >58,000 individual animals, spanning 30 species of fish, reptiles, birds, mammals and insects, 80% of systems exhibit strong positive relationships between local density and network centrality. However, >80% of relationships are nonlinear and 75% are shallower at higher values, indicating saturating trends that probably emerge as a result of demographic and behavioural processes that counteract density's effects. These are stronger and less saturating in spatial compared with social networks, as individuals become disproportionately spatially connected rather than socially connected at higher densities. Consequently, ecological processes that depend on spatial connections are probably more density dependent than those involving social interactions. These findings suggest fundamental scaling rules governing animal social dynamics, which could help to predict network structures in novel systems.

Host personality can markedly affect parasite transmission. Especially for parasites with indirect transmission through the environment, the effects of consistent among-individual differences in behavior may have both direct and indirect components. For example, personality may mediate both how hosts respond to infected individuals and the likelihood that hosts indirectly interact with infected conspecifics (e.g., by visiting patches infected hosts have previously contaminated). Integrating parasites, personality, and these different kinds of interaction networks constitutes a key step toward understanding transmission in natural systems. We evaluated these elements using a 5-year field study of a wild population of sleepy lizards, Tiliqua rugosa, and their tick parasites, which transmit among lizards through lizards' shared use of refuges. Using Bayesian models, we evaluated (1) predictors of lizard infestation probability and intensity (i.e., average tick count when infested) and (2) relationships among the predictors. We used the latter set of models to assess indirect relationships between the predictors and the infestation metrics. As predictors, we used lizards' infestation "risk" (derived from a time-lagged refuge sharing transmission network), traits (sex, mass, and the personality axes aggression and boldness), space use (number of unique refuges used and home range overlap with other lizards), and measures of synchronous social interactions (i.e., edge weight and degree). We found both indirect and direct connections between our predictors and tick infestation. For example, boldness was positively directly associated with infection intensity and indirectly positively associated with both infestation probability and intensity via intermediary connections with social network interaction and risk. Using more unique refuges, on the other hand, was indirectly negatively associated with infestation probability (via reduced risk), but directly positively associated with infestation probability, indicating a potential trade-off in the anti-parasite benefits of using more refuges. Our results emphasize that (1) multiple aspects of host behavior may associate with parasite infection, (2) these components may proceed through both direct and indirect pathways, and (3) multiple pathways should be considered together because the pathways may have compounding or counteracting effects.

Host behavior and parasite infection reciprocally interact, but this dynamic is rarely studied experimentally in the field with multiple behaviors. We investigated the interplay between parasitism and host behavior via an in situ experimental tick infestation of a wild population of sleepy lizards, Tiliqua rugosa. Using Bayesian models, we assessed the relationship between experimental infestation and lizard aggression and boldness before and after infestation. First, we tested whether lizard aggression and boldness prior to infestation predicted the probability of tick attachment in the infestation experiment. Second, we evaluated whether experimental infestation affected subsequent lizard aggression and boldness. We found that aggression and boldness related interactively with infestation: for unaggressive lizards, higher boldness was associated with reduced experimental infestation success, but the opposite occurred for aggressive individuals. Second, increased tick infestation did not affect post-infestation aggression, but tended to increase boldness. Taken together, these results highlight the potential for feedbacks between parasites and multi-dimensional host behaviors. Although behavior is known to affect parasite loads, and parasites, in turn, can affect host behavior, it is unclear how personality interacts with parasite infestation. We experimentally infected a wild lizard population with ticks to study how lizard personality interacted with parasite loads in complex feedback loops. We found that personality affected parasite loads and that parasites, in turn, affected hosts with different personality types in distinct ways.

Recent evidence suggests that individuals differ in foraging tactics and this variation is often linked to an individual's behavioural type (BT). Yet, while foraging typically comprises a series of search and handling steps, empirical investigations have rarely considered BT-dependent effects across multiple stages of the foraging process, particularly in natural settings. In our long-term sleepy lizard (Tiliqua rugosa) study system, individuals exhibit behavioural consistency in boldness (measured as an individual's willingness to approach a novel food item in the presence of a threat) and aggressiveness (measured as an individual's response to an 'attack' by a conspecific dummy). These BTs are only weakly correlated and have previously been shown to have interactive effects on lizard space use and movement, suggesting that they could also affect lizard foraging performance, particularly in their search behaviour for food. To investigate how lizards' BTs affect their foraging process in the wild, we supplemented food in 123 patches across a 120-ha study site with three food abundance treatments (high, low and no-food controls). Patches were replenished twice a week over the species' entire spring activity season and feeding behaviours were quantified with camera traps at these patches. We tracked lizards using GPS to determine their home range (HR) size and repeatedly assayed their aggressiveness and boldness in designated assays. We hypothesised that bolder lizards would be more efficient foragers while aggressive ones would be less attentive to the quality of foraging patches. We found an interactive BT effect on overall foraging performance. Individuals that were both bold and aggressive ate the highest number of food items from the foraging array. Further dissection of the foraging process showed that aggressive lizards in general ate the fewest food items in part because they visited foraging patches less regularly, and because they discriminated less between high and low-quality patches when revisiting them. Bolder lizards, in contrast, ate more tomatoes because they visited foraging patches more regularly, and ate a higher proportion of the available tomatoes at patches during visits. Our study demonstrates that BTs can interact to affect different search and handling components of the foraging process, leading to within-population variation in foraging success. Given that individual differences in foraging and movement will influence social and ecological interactions, our results highlight the potential role of BT's in shaping individual fitness strategies and population dynamics.

High population density should drive individuals to more frequently share space and interact, producing better-connected spatial and social networks. Despite this widely-held assumption, it remains unconfirmed how local density generally drives individuals' positions within wild animal networks. We analysed 34 datasets of simultaneous spatial and social behaviour in >55,000 individual animals, spanning 28 species of fish, reptiles, birds, mammals, and insects. >80% of systems exhibited strongly positive relationships between local density and network centrality, providing broad empirical evidence that local density increases connectedness at the individual level. However, >75% of density-connectedness relationships were nonlinear, and density's importance declined at higher values in >70% of systems, signifying saturating effects. Density's effect was much stronger and less saturating for spatial than social networks, suggesting population density drives individuals to become disproportionately spatially connected rather than socially. These findings reveal fundamental trends underlying societal structuring, with widespread behavioural, ecological, and evolutionary implications. ### Competing Interest Statement The authors have declared no competing interest.

Home ranges (HRs), the regions within which animals interact with their environment, constitute a fundamental aspect of their ecology. HR sizes and locations commonly reflect costs and benefits associated with diverse social, biotic, and abiotic factors. Less is known, however, about how these factors affect intraspecific variation in HR size or fidelity (the individual's tendency to maintain the same HR location over time) or whether variation in these features emerge from consistent differences among individuals or among the sites they occupy. To address this knowledge gap, we used an extensive GPS-tracking data set of a long-lived lizard, the sleepy lizard (Tiliqua rugosa), which included repeated observations of multiple individuals across years. We tested how three categories of predictors-(1) lizard characteristics (sex, aggressiveness, and parasitic tick counts), (2) environmental characteristics (precipitation, food, and refuge quality), and (3) social conditions (conspecific overlap and number of neighbors)-affected HR size and fidelity. We found that individuals differed consistently in the size and fidelity of annual HRs (with a repeatability of 0.58 and 0.33, respectively), and that all three categories of predictors affected both HR size and fidelity. For example, HRs were smaller in areas with more food, and males had larger HRs than females. In addition, more aggressive lizards tended to have larger HRs. Conspecific overlap and number of individuals that a lizard interacted with (social network degree) had an interactive effect on HR size where individuals whose HRs overlapped more with neighbors had larger HRs, and this effect was particularly strong for individuals that interacted with more neighbors. HR fidelity declined over time (HR locations drifted from year to year), but individuals differed consistently in this rate of drift. The fact that HR size was consistent despite drifting locations suggests that lizard HRs reflect individual traits (e.g., habitat choice criteria that differ among individuals), rather than simple heterogeneity among sites. Overall, these findings demonstrate (1) both strong, long-term, within-individual consistency and between-individual differences in space use and (2) combined effects of individual traits, social conditions, and environmental characteristics on animal HRs, with implications for diverse ecological processes.

Individual variation in movement is profoundly important for fitness and offers key insights into the spatial and temporal dynamics of populations and communities. Nonetheless, individual variation in fine-scale movement behaviours is rarely examined even though animal tracking devices offer the long-term, high-resolution, repeatable data in natural conditions that are ideal for studying this variation. Furthermore, of the few studies that consider individual variation in movement, even fewer also consider the internal traits and environmental factors that drive movement behaviour which are necessary for contextualising individual differences in movement patterns. In this study, we GPS tracked a free-ranging population of sleepy lizards Tiliqua rugosa, each Austral spring over 5 years to examine consistent among-individual variation in movement patterns, as well as how these differences were mediated by key internal and ecological factors. We found that individuals consistently differed in a suite of weekly movement traits, and that these traits strongly covaried among-individuals, forming movement syndromes. Lizards fell on a primary movement continuum, from 'residents' that spent extended periods of time residing within smaller core areas of their home range, to 'explorers' that moved greater distances and explored vaster areas of the environment. Importantly, we also found that these consistent differences in lizard movement were related to two ecologically important animal personality traits (boldness and aggression), their sex, key features of the environment (including food availability, and a key water resource), habitat type and seasonal variation (cool/moist vs. hot/drier) in environmental conditions. Broadly, these movement specialisations likely reflect variation in life-history tactics including foraging and mating tactics that ultimately underlie key differences in space use. Such information can be used to connect phenotypic population structure to key ecological and evolutionary processes, for example social networks and disease-transmission pathways, further highlighting the value of examining individual variation in movement behaviour.

Ecologists have long been interested in linking individual behaviour with higher level processes. For motile species, this 'upscaling' is governed by how well any given movement strategy maximizes encounters with positive factors and minimizes encounters with negative factors. Despite the importance of encounter events for a broad range of ecological processes, encounter theory has not kept pace with developments in animal tracking or movement modelling. Furthermore, existing work has focused primarily on the relationship between animal movement and encounter rates while the relationship between individual movement and the spatial locations of encounter events in the environment has remained conspicuously understudied. Here, we bridge this gap by introducing a method for describing the long-term encounter location probabilities for movement within home ranges, termed the conditional distribution of encounters (CDE). We then derive this distribution, as well as confidence intervals, implement its statistical estimator into open-source software and demonstrate the broad ecological relevance of this distribution. We first use simulated data to show how our estimator provides asymptotically consistent estimates. We then demonstrate the general utility of this method for three simulation-based scenarios that occur routinely in biological systems: (a) a population of individuals with home ranges that overlap with neighbours; (b) a pair of individuals with a hard territorial border between their home ranges; and (c) a predator with a large home range that encompassed the home ranges of multiple prey individuals. Using GPS data from white-faced capuchins Cebus capucinus, tracked on Barro Colorado Island, Panama, and sleepy lizards Tiliqua rugosa, tracked in Bundey, South Australia, we then show how the CDE can be used to estimate the locations of territorial borders, identify key resources, quantify the potential for competitive or predatory interactions and/or identify any changes in behaviour that directly result from location-specific encounter probability. The CDE enables researchers to better understand the dynamics of populations of interacting individuals. Notably, the general estimation framework developed in this work builds straightforwardly off of home range estimation and requires no specialized data collection protocols. This method is now openly available via the ctmm R package.

Despite growing attention to the ecological and evolutionary importance of consistent individual differences in behaviour (animal personality), long-term field studies quantifying factors associated with behavioural repeatability remain rare. Here, we studied animal personalities over an 8-year period, representing 6 study years, in a wild population of the long-lived sleepy lizard, Tiliqua rugosa. Using Bayesian generalized linear mixed models for 170 unique individuals and a total of 379 lizard-years, we (1) considered the effects of a suite of predictors - particularly lizard sex, mass and tick counts - on lizard aggression and boldness (2) assessed repeatability (i.e. consistent differences among individuals), of these behaviours over different timescales and between lizard sexes and (3) evaluated the correlation, or behavioural syndrome, between aggression and boldness. We found that males were marginally more aggressive and bolder than females, mass had no significant effect and tick loads exhibited a positive relationship with aggression and boldness. For repeatability, we found that even with the long timescales considered in this study, aggression and boldness were both repeatable - across the entire data set (-0.4 and -0.3, respectively) using all lizards, as well as among years (-0.4 and -0.4, respectively) using lizards observed in multiple years (93 for aggression, 73 for boldness). Repeatability did not differ substantially between the sexes. We found no syndrome between aggression and boldness - despite a weak positive correlation in multivariate mixed models, the 95% credible interval for this correlation included zero. Our results are notable because they demonstrate that wild animals may exhibit consistent personality differences in ecologically relevant behaviours over extended periods even in the face of substantial temporal variation in ecological and social factors, a fact that has likely ecological and evolutionary consequences. (C)& nbsp;2021 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Natal dispersal plays an important role in connecting individual animal behavior with ecological processes at all levels of biological organization. As urban environments are rapidly increasing in extent and intensity, understanding how urbanization influences these long distance movements is critical for predicting the persistence of species and communities. There is considerable variation in the movement responses of individuals within a species, some of which is attributed to behavioral plasticity which interacts with experience to produce interindividual differences in behavior. For natal dispersers, much of this experience occurs in the natal home range. Using data collected from VHF collared coyotes (Canis latrans) in the Chicago Metropolitan Area we explored the relationship between early life experience with urbanization and departure, transience, and settlement behavior. Additionally, we looked at how early life experience with urbanization influenced survival to adulthood and the likelihood of experiencing a vehicle related mortality. We found that coyotes with more developed habitat in their natal home range were more likely to disperse and tended to disperse farther than individuals with more natural habitat in their natal home range. Interestingly, our analysis produced mixed results for the relationship between natal habitat and habitat selection during settlement. Finally, we found no evidence that early life experience with urbanization influenced survival to adulthood or the likelihood of experiencing vehicular mortality. Our study provides evidence that early life exposure influences dispersal behavior; however, it remains unclear how these differences ultimately affect fitness.

Individual hosts vary substantially in their parasite loads. However, whether individual hosts have consistently different loads remains uncertain. If so, hosts that have consistently high parasite loads may serve as key reservoirs or super‐spreaders. Thus, identifying whether individuals persistently differ in their parasitism and the factors that explain these patterns constitute important issues for disease ecology and management. To investigate these topics, we examined nine years of tick counts in a wild population of sleepy lizards Tiliqua rugosa . Lizards were individually marked, and throughout their activity season, often across several years, we repeatedly assessed lizards’ ticks (to stage – larva, nymph, adult male and adult female – and species, either Bothriocroton hydrosauri or Amblyomma limbatum ). Using these repeated individual measures, we determined whether tick counts were repeatable. Then, we tested predictors of average tick counts, particularly lizard mass, sex, behavioural type (aggression and boldness), and the distance between lizards’ home range centre and a road transecting the study site (an area of greater food and lizard activity). We found that lizards exhibited consistent individual differences in tick loads both within and across years. Within‐lizard yearly average counts of larvae and nymphs were positively correlated. Lizards closer to the road tended to have more larvae and nymphs of both species and more adult B. hydrosauri . Sex did not affect tick counts. Mass differentially affected adult female A. limbatum and adult male B. hydrosauri tick counts. Intriguingly, lizards with above average aggression but below average boldness, or vice versa, tended to have higher average adult female B. hydrosauri tick counts. Ultimately, our results demonstrate that lizards differed consistently in their tick counts, indicating that lizard parasitism may constitute a phenotypic trait of the individual, with implications for both host–parasite dynamics and broader host ecology.

It is well established that parasites can have profound effects on the behaviour of host organisms, and that individual differences in behaviour can influence susceptibility to parasite infections. Recently, two major themes of research have developed. First, there has been a growing interest in the proximate, mechanistic processes underpinning parasite-associated behaviour change, and the interactive roles of the neuro-, immune, and other physiological systems in determining relationships between behaviour and infection susceptibility. Secondly, as the study of behaviour has shifted away from one-off measurements of single behaviours and towards a behavioural syndromes/personality framework, research is starting to focus on the consequences of parasite infection for temporal and contextual consistency of behaviour, and on the implications of different personality types for infection susceptibility. In addition, there is increasing interest in the potential for relationships between cognition and personality to also have implications for host-parasite interactions. As models well-suited to both the laboratory study of behaviour and experimental parasitology, teleost fish have been used as hosts in many of these studies. In this review we provide a broad overview of the range of mechanisms that potentially generate links between fish behaviour, personality, and parasitism, and illustrate these using examples drawn from the recent literature. In addition, we examine the potential interactions between cognition, personality and parasitism, and identify questions that may be usefully investigated with fish models.