The response of a sleepy lizard social network to altered ecological conditions

Knowledge transmission, culture and the consequences of social disruption in wild elephants

Cultural knowledge is widely presumed to be important for elephants. In all three elephant species, individuals tend to congregate around older conspecifics, creating opportunities for social transmission. However, direct evidence of social learning and cultural traditions in elephants is scarce. Here, we briefly outline that evidence then provide a systematic review of how elephant societies respond to the loss of potentially knowledgeable individuals or opportunities for knowledge transfer, which we characterize as social disruption. We consider observations from 95 peer-reviewed, primary research papers that describe disruption to elephant societies or networks via the removal or death of individuals. Natural deaths were mentioned in 14 papers, while 70 detailed human-caused deaths or disruption. Grouping descriptions according to consequences for behaviour and sociality, and demography and fitness, we show that severely disrupted populations are less cohesive, may exhibit reduced fitness or calf survival and respond inappropriately to threats and predators. We suggest that severe social disruption can inhibit or break potential pathways of information transmission, providing indirect evidence for the role of social transmission in elephants. This has implications for elephant conservation amid increasing anthropogenic change across their habitats.This article is part of the theme issue 'Animal culture: conservation in a changing world'.

Plains Zebras Prioritize Foraging Without Sacrificing Social Bonds During a Severe Drought

Anthropogenically induced climate change has significantly increased the frequency of acute weather events, such as drought. As human activities amplify environmental stresses, animals may be forced to prioritize survival over behaviors less crucial to immediate fitness, such as socializing. Yet, social bonds may also enable individuals to weather the deleterious effects of environmental conditions. We investigated how the highly social plains zebra (Equus quagga) modify their activity budgets, social networks, and multimodal communication during a drought. Although animals prioritized feeding and the number of social interactions dramatically decreased in the late drought period, social associations remained robust. We observed age/sex class-specific changes in social behavior, reflecting the nutritional needs and social niche of each individual. Stallions devoted more time to greeting behaviors, which could mitigate harassment by bachelor males and facilitate grazing time for the females of the harem. Juveniles significantly increased time spent active socializing, despite mothers showing the greatest decrease in the number of social interactions. Instead, unrelated, nonlactating females served as social partners, accommodating both juveniles' social needs and lactating mothers' nutritive requirements. Using a network-based representation of multimodal communication, we observed a decrease in the number of signals used during the drought. Individuals used less diverse multimodal combinations, particularly in the costly context of aggression. These findings illustrate how social roles and differential responses to acute environmental stress within stable social groups may contribute to species resilience, and how communication flexibly responds to facilitate both survival and sociality under harsh environmental conditions.

Submissive behavior is affected by territory structure in a social fish

Group living may engender conflict over food, reproduction, or other resources and individuals must be able to manage conflict for social groups to persist. Submission signals are an adaptation for establishing and maintaining social hierarchy position, allowing a subordinate individual to avoid protracted and costly aggressive interactions with dominant individuals. In the daffodil cichlid fish (Neolamprologus pulcher), subordinates may use submission signals to resolve conflicts with dominant individuals and maintain their social status within the group. The complexity of the physical environment may affect the value of submission signals compared with fleeing or avoidance, which may require certain physical features such as shelters to be effective. We investigated how the ecological context affected the expression of submission in subordinate daffodil cichlids by examining their behavior under different arrangements of the physical environment within their territories. We altered the number of shelters provided to daffodil cichlid groups and compared the interactions between dominant and subordinate individuals under each shelter condition by scoring the social and cooperative behaviors of the group members. We found that behaviors of group members were modulated by the environment: subordinates displayed fewer submission and fleeing behaviors in more structurally complex environments and dominants were more aggressive to subordinates when more shelters were present. Our results help to elucidate the role of the physical environment in the modulation of social interactions in group-living animals and may have implications for the welfare of captively housed social cichlid groups.

Resource manipulation reveals interactive phenotype-dependent foraging in free-ranging lizards

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.

Emergent social structure is typically not associated with survival in a facultatively social mammal

For social animals, group social structure has important consequences for disease and information spread. While prior studies showed individual connectedness within a group has fitness consequences, less is known about the fitness consequences of group social structure for the individuals who comprise the group. Using a long-term dataset on a wild population of facultatively social yellow-bellied marmots (Marmota flaviventer), we showed social structure had largely no relationship with survival, suggesting consequences of individual social phenotypes may not scale to the group social phenotype. An observed relationship for winter survival suggests a potentially contrasting direction of selection between the group and previous research on the individual level; less social individuals, but individuals in more social groups experience greater winter survival. This work provides valuable insights into evolutionary implications across social phenotypic scales.

Social responses to the natural loss of individuals in Barbary macaques

In recent years, there has been considerable interest in investigating how animal social structure is affected by the loss of individuals. This is often achieved using simulations that generate predictions regarding how the removal of ‘key’ individuals from a group affects network structure. However, little is known about the effects of such removals in wild and free-ranging populations, particularly the extent to which naturally occurring mortality events and the loss of a large proportion of individuals from a social group affects the overall structure of a social network. Here, we used data from a population of wild Barbary macaques (Macaca sylvanus) that was exposed to an exceptionally harsh winter, culminating in the death of 64% of the adults from two groups. We analysed how social interaction patterns among surviving individuals were affected by the natural loss of group members using social networks based on affiliative (i.e., grooming) and aggressive social interactions. We show that only the structure of the pre-decline grooming networks was conserved in the post-decline networks, suggesting that grooming, but not aggression networks are resilient against the loss of group members. Surviving group members were not significantly different from the non-survivors in terms of their affiliative and agonistic relationships, and did not form assorted communities in the pre-decline networks. Overall, our results suggest that in primates, patterns of affiliative interactions are more resilient to changes in group composition than aggressive interaction patterns, which tend to be used more flexibly in new conditions.

Using network synchrony to identify drivers of social dynamics

Social animals frequently show dynamic social network patterns, the consequences of which are felt at the individual and group level. It is often difficult, however, to identify what drivers are responsible for changes in these networks. We suggest that patterns of network synchronization across multiple social groups can be used to better understand the relative contributions of extrinsic and intrinsic drivers. When groups are socially separated, but share similar physical environments, the extent to which network measures across multiple groups covary (i.e. network synchrony) can provide an estimate of the relative roles of extrinsic and intrinsic drivers. As a case example, we use allogrooming data from three adjacent vervet monkey groups to generate dynamic social networks. We found that network strength was strongly synchronized across the three groups, pointing to shared extrinsic environmental conditions as the driver. We also found low to moderate levels of synchrony in network modularity, suggesting that intrinsic social processes may be more important in driving changes in subgroup formation in this population. We conclude that patterns of network synchronization can help guide future research in identifying the proximate mechanisms behind observed social dynamics in animal groups.

Group composition of individual personalities alters social network structure in experimental populations of forked fungus beetles

Social network structure is a critical group character that mediates the flow of information, pathogens and resources among individuals in a population, yet little is known about what shapes social structures. In this study, we experimentally tested whether social network structure depends on the personalities of individual group members. Replicate groups of forked fungus beetles (Bolitotherus cornutus) were engineered to include only members previously assessed as either more social or less social. We found that individuals expressed consistent personalities across social contexts, exhibiting repeatable numbers of interactions and numbers of partners. Groups composed of more social individuals formed networks with higher interaction rates, higher tie density, higher global clustering and shorter average shortest paths than those composed of less social individuals. We highlight group composition of personalities as a source of variance in group traits and a potential mechanism by which networks could evolve.

Personality, spatiotemporal ecological variation and resident/explorer movement syndromes in the sleepy lizard

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.

How demographic processes shape animal social networks

Demographic processes play a key role in shaping the patterns of social relations among individuals in a population. Social network analysis is a powerful quantitative tool for assessing the social structure formed by associations between individuals. However, demographic processes are rarely accounted for in such analyses. Here, we summarize how the structure of animal social networks is shaped by the joint effects of social behavior and turnover of individuals and suggest how a deeper understanding of these processes can open new, exciting avenues for research. Death or dispersal can have the direct effect of removing an individual and all its social connections, and can also have indirect effects, spurring changes in the distribution of social connections between remaining individuals. Recruitment and integration of juveniles and immigrant into existing social networks are critical to the emergence and persistence of social network structure. Together, these behavioral responses to loss and gain of social partners may impact how societies respond to seasonal or catastrophic turnover events. The fitness consequences of social position (e.g., survival and reproductive rates) may also create feedback between the social network structure and demography. Understanding how social structure changes in response to turnover of individuals requires further integration between long-term field studies and network modeling methods. These efforts will likely yield new insights into the connections between social networks and life history, ecological change, and evolutionary dynamics.

Intragroup social dynamics vary with the presence of neighbors in a cooperatively breeding fish

Conflict is an inherent part of social life in group-living species. Group members may mediate conflict through submissive and affiliative behaviors, which can reduce aggression, stabilize dominance hierarchies, and foster group cohesion. The frequency and resolution of within-group conflict may vary with the presence of neighboring groups. Neighbors can threaten the territory or resources of the whole group, promoting behaviors that foster within-group cohesion. However, neighbors may also foster conflict of interests among group members: opportunities for subordinate dispersal may alter conflict among dominants and subordinates while opportunities for extra-pair reproduction may increase conflict between mates. To understand how neighbors mediate within-group conflict in the cooperatively breeding fish Neolamprologus pulcher, we measured behavioral dynamics and social network structure in isolated groups, groups recently exposed to neighbors, and groups with established neighbors. Aggression and submission between the dominant male and female pair were high in isolated groups, but dominant aggression was directly primarily at subordinates when groups had neighbors. This suggests that neighbors attenuate conflict between mates and foster conflict between dominants and subordinates. Further, aggression and submission between similarly sized group members were most frequent when groups had neighbors, suggesting that neighbors induce rank-related conflict. We found relatively little change in within-group affiliative networks across treatments, suggesting that the presence of neighbors does not alter behaviors associated with promoting group cohesion. Collectively, these results provide some of the first empirical insights into the extent to which intragroup behavioral networks are mediated by intergroup interactions and the broader social context.

Social network dynamics precede a mass eviction in group-living rhesus macaques

Network dynamics can reveal information about the adaptive function of social behaviour and the extent to which social relationships can flexibly respond to extrinsic pressures. Changes in social networks occur following changes to the social and physical environment. By contrast, we have limited understanding of whether changes in social networks precede major group events. Permanent evictions can be important determinants of gene flow and population structure and are a clear example of an event that might be preceded by social network dynamics. Here we examined the social networks of a group of rhesus macaques, Macaca mulatta, in the 2 years leading up to the eviction of 22% of adult females, which are the philopatric sex. We found that females engaged in the same amount of aggression and grooming in the 2 years leading up to the eviction but that there were clear changes in their choice of social partners. Females that would eventually be evicted received more aggression from lower-ranking females as the eviction approached. Evicted females also became more discriminating in their grooming relationships in the year nearer the split, showing a greater preference for one another and becoming more cliquish. Put simply, the females that would later be evicted continued to travel with the rest of the group as the eviction approached but were less likely to interact with other group members in an affiliative manner. These results have potential implications for understanding group cohesion and the balance between cooperation and competition that mediates social groups.

Social networks: a tool for assessing the impact of perturbations on wildlife behaviour and implications for pathogen transmission

Wildlife are increasingly subject to perturbations, which can impact pathogen transmission and lead to disease emergence. While a myriad of factors influence disease dynamics in wildlife, behaviour is emerging as a major influence. In this review, we examine how perturbations alter the behaviour of individuals and how, in turn, disease transmission may be impacted, with a focus on the use of network models as a powerful tool. There are emerging hypotheses as to how networks respond to different types of perturbations. The broad effects of perturbations make predicting potential outcomes and identifying mitigation opportunities for disease emergence critical; yet, the current paucity of data makes identification of underlying trends difficult. Social network analysis facilitates a mechanistic approach to how perturbation-induced behavioural changes result in shifts in pathogen transmission. However, the field is still developing, and future work should strive to address current deficits. There is particular need for empirical data to support modelling predictions and increased inclusion of pathogen monitoring in network studies.

When the going gets tough: behavioural type-dependent space use in the sleepy lizard changes as the season dries

Understanding space use remains a major challenge for animal ecology, with implications for species interactions, disease spread, and conservation. Behavioural type (BT) may shape the space use of individuals within animal populations. Bolder or more aggressive individuals tend to be more exploratory and disperse further. Yet, to date we have limited knowledge on how space use other than dispersal depends on BT. To address this question we studied BT-dependent space-use patterns of sleepy lizards (Tiliqua rugosa) in southern Australia. We combined high-resolution global positioning system (GPS) tracking of 72 free-ranging lizards with repeated behavioural assays, and with a survey of the spatial distributions of their food and refuge resources. Bayesian generalized linear mixed models (GLMM) showed that lizards responded to the spatial distribution of resources at the neighbourhood scale and to the intensity of space use by other conspecifics (showing apparent conspecific avoidance). BT (especially aggressiveness) affected space use by lizards and their response to ecological and social factors, in a seasonally dependent manner. Many of these effects and interactions were stronger later in the season when food became scarce and environmental conditions got tougher. For example, refuge and food availability became more important later in the season and unaggressive lizards were more responsive to these predictors. These findings highlight a commonly overlooked source of heterogeneity in animal space use and improve our mechanistic understanding of processes leading to behaviourally driven disease dynamics and social structure.

Exploration of unpredictable environments by networked groups

Information sharing is a critical task for group-living animals. The pattern of sharing can be modeled as a network whose structure can affect the decision-making performance of individual members as well as that of the group as a whole. A fully connected network, in which each member can directly transfer information to all other members, ensures rapid sharing of important information, such as a promising foraging location. However, it can also impose costs by amplifying the spread of inaccurate information (if, for example the foraging location is actually not profitable). Thus, an optimal network structure should balance effective sharing of current knowledge with opportunities to discover new information. We used a computer simulation to measure how well groups characterized by different network structures (fully connected, small world, lattice, and random) find and exploit resource peaks in a variable environment. We found that a fully connected network outperformed other structures when resource quality was predictable. When resource quality showed random variation, however, the small world network was better than the fully connected one at avoiding extremely poor outcomes. These results suggest that animal groups may benefit by adjusting their information-sharing network structures depending on the noisiness of their environment.

Lizard movement tracks: variation in path re-use behaviour is consistent with a scent-marking function

Individual movement influences the spatial and social structuring of a population. Animals regularly use the same paths to move efficiently to familiar places, or to patrol and mark home ranges. We found that Australian sleepy lizards (Tiliqua rugosa), a monogamous species with stable pair-bonds, repeatedly used the same paths within their home ranges and investigated whether path re-use functions as a scent-marking behaviour, or whether it is influenced by site familiarity. Lizards can leave scent trails on the substrate when moving through the environment and have a well-developed vomeronasal system to detect and respond to those scents. Path re-use would allow sleepy lizards to concentrate scent marks along these well-used trails, advertising their presence. Hypotheses of mate attraction and mating competition predict that sleepy lizard males, which experience greater intra-sexual competition, mark more strongly. Consistent with those hypotheses, males re-used their paths more than females, and lizards that showed pairing behaviour with individuals of the opposite sex re-used paths more than unpaired lizards, particularly among females. Hinterland marking is most economic when home ranges are large and mobility is low, as is the case in the sleepy lizard. Consistent with this strategy, re-used paths were predominantly located in the inner 50% home range areas. Together, our detailed movement analyses suggest that path re-use is a scent marking behaviour in the sleepy lizard. We also investigated but found less support for alternative explanations of path re-use behaviour, such as site familiarity and spatial knowledge. Lizards established the same number of paths, and used them as often, whether they had occupied their home ranges for one or for more years. We discuss our findings in relation to maintenance of the monogamous mating system of this species, and the spatial and social structuring of the population.

Artificial Water Point for Livestock Influences Spatial Ecology of a Native Lizard Species

Pastoralism is a major agricultural activity in drier environments, and can directly and indirectly impact native species in those areas. We investigated how the supply of an artificial watering point to support grazing livestock affected movement and activity patterns of the Australian sleepy lizard (Tiliqua rugosa) during a drought year. We observed 23 adult lizards; six had access to a dam, whereas 17 lizards did not. Lizards with access to the dam had larger home ranges, were substantially active on more days (days with >100 steps), and moved more steps per day compared to lizards that did not have access to the dam, both during the early and late period of our observation. Furthermore, while the two groups of lizards had similar body condition early in the season, they differed later in the season. Lizards with dam access retained, whereas lizards without access lost body condition. Local heterogeneity in access to an artificial water resource resulted in spatially dependent behavioural variation among sleepy lizard individuals. This suggests that sleepy lizards have flexible responses to changing climatic conditions, depending on the availability of water. Furthermore, while reducing activity appears a suitable short term strategy, if harsh conditions persist, then access to dams could be of substantial benefit and could support sustained lizard activity and movement and allow maintenance of body condition. Hence, artificial watering points, such as the dams constructed by pastoralists, may provide local higher quality refugia for sleepy lizards and other species during drought conditions.

Tick exposure and extreme climate events impact survival and threaten the persistence of a long-lived lizard

Assessing the impacts of multiple, often synergistic, stressors on the population dynamics of long-lived species is becoming increasingly important due to recent and future global change. Tiliqua rugosa (sleepy lizard) is a long-lived skink (>30 years) that is adapted to survive in semi-arid environments with varying levels of parasite exposure and highly seasonal food availability. We used an exhaustive database of 30 years of capture-mark-recapture records to quantify the impacts of both parasite exposure and environmental conditions on the lizard's survival rates and long-term population dynamics. Lizard abundance was relatively stable throughout the study period; however, there were changing patterns in adult and juvenile apparent survival rates, driven by spatial and temporal variation in levels of tick exposure and temporal variation in environmental conditions. Extreme weather events during the winter and spring seasons were identified as important environmental drivers of survival. Climate models predict a dramatic increase in the frequency of extreme hot and dry winter and spring seasons in our South Australian study region; from a contemporary probability of 0.17 up to 0.47-0.83 in 2080 depending on the emissions scenario. Our stochastic population model projections showed that these future climatic conditions will induce a decline in the abundance of this long-lived reptile of up to 67% within 30 years from 2080, under worst case scenario modelling. The results have broad implications for future work investigating the drivers of population dynamics and persistence. We highlight the importance of long-term data sets and accounting for synergistic impacts between multiple stressors. We show that predicted increases in the frequency of extreme climate events have the potential to considerably and negatively influence a long-lived species, which might previously have been assumed to be resilient to environmental perturbations.

Current insecticide treatments used in locust control have less of a short-term impact on Australian arid-zone reptile communities than does temporal variation

Context Despite the regular use of pesticides to control locusts, there is a lack of information on the effects of locust-control treatments on reptiles worldwide. Exposure to pesticides poses a significant potential hazard to small reptiles, both from the direct effects of exposure, and indirectly because of their largely insectivorous diet and small home ranges. Aims Our study aimed to monitor the effects of two insecticides applied operationally for locust control in Australia. A phenyl pyrazole pesticide, fipronil, and a fungal biopesticide, Metarhizium acridium (Green Guard®), were applied aerially in either a barrier or block treatment in the absence of dense locust populations, and effects on non-target arid-zone reptiles were measured. Methods We monitored reptile-abundance and community-composition responses to treatments using a large field-based pitfall-trapping experiment, with replicated control and spraying treatments, which approximated the scale of aerial-based locust-control operations in Australia. Key results Neither reptile abundance nor community composition was significantly affected by locust-control treatments. However, both abundance and community composition as detected by pitfall trapping changed over time, in both control and treatment plots, possibly as a result of a decrease in annual rainfall. Conclusions The absence of any significant short-term pesticide treatment effects in our study suggests that the two locust-control application methods studied present a relatively insignificant hazard to reptiles at our site, based on a single application. Similar to other areas of Australia, climate and other factors are likely to be stronger drivers of reptile abundance and community structure. Implications Monitoring over an area that approximates the scale of the current locust-control operations is an important step in understanding the possible effects of current pesticide exposure on reptile populations and will inform insecticide risk assessments in Australia. However, important information on the immediate response of individuals to insecticide application and long-term effects of exposure are missing. The preliminary research reported in the present paper should be complemented by future investigations on long-term and sublethal impacts of pesticide exposure on Australian native reptiles and the possible benefits provided to reptiles by the resource pulses represented in untreated high-density locust populations.