Consistent individual differences and population plasticity in network-derived sociality: An experimental manipulation of density in a gregarious ungulate

Abstract

In many taxa, individual social traits appear to be consistent across time and context, thus meeting the criteria for animal personality. How these differences are maintained in response to changes in population density is unknown, particularly in large mammals, such as ungulates. Using a behavioral reaction norm (BRN) framework, we examined how among- and within-individual variation in social connectedness, measured using social network analyses, change as a function of population density. We studied a captive herd of elk (Cervus canadensis) separated into a group of male elk and a group of female elk. Males and females were exposed to three different density treatments and we recorded social associations between individuals with proximity-detecting radio-collars fitted to elk. We constructed social networks using dyadic association data and calculated three social network metrics reflective of social connectedness: eigenvector centrality, graph strength, and degree. Elk exhibited consistent individual differences in social connectedness across densities; however, they showed little individual variation in their response to changes in density, i.e., individuals oftentimes responded plastically, but in the same manner to changes in density. Female elk had highest connectedness at an intermediate density. In contrast, male elk increased connectedness with increasing density. Whereas this may suggest that the benefits of social connectedness outweigh the costs of increased competition at higher density for males, females appear to exhibit a threshold in social benefits (e.g. predator detection and forage information). Our study illustrates the importance of viewing social connectedness as a density-dependent trait, particularly in the context of plasticity. Moreover, we highlight the need to revisit our understanding of density dependence as a population-level phenomenon by accounting for consistent individual differences not only in social connectedness, but likely in other ecological processes (e.g., predator-prey dynamics, mate choice, disease transfer).

Wild songbirds exhibit consistent individual differences in inter-specific social behaviour

“…For example, repeatability scores reported for migration, mate preference, and parental behaviours were on average less than 0.3, whereas week-to-week repeatability values observed in this study ranged from 0.4 to 0.6, with. Consistent individual differences in social network position were previously shown in only a few populations where social behaviour was studied in a conspecific context (e.g., Jacoby et al 2014; Menz et al 2017; O’Brien et al 2018), including a study on our system, which noted inter-individual differences and reported similar repeatability in great tit social strategies (group size: R = 0.43-0.64, degree: R = 0.46-0.61, association strength: R = 0.41-0.64) in a single-species context (Aplin et al 2015). Here, we extend findings of studies on single-species systems by showing that individuals vary in their heterospecific social associations in much the same way as was previously reported within species.…”

“…Hence, a key first step in relating fitness consequences to social network position is to understand the distribution and consistency of individual variation in behaviour by characterising individual interaction patterns and social phenotypes. Consistency in social behaviour is often assumed, but only a few studies have shown that individuals can express consistent social phenotypes, by repeatedly measuring and comparing their mebehaviour over larger time spans (Blumstein et al 2013; Jacoby et al 2014; Aplin et al 2015; Menz et al 2017; O’Brien et al 2018). Whether individuals also express consistent social strategies in a multi-species context is yet to be explored.…”

Unifying spatial and social network analysis in disease ecology

“…Although spatial‐social correlations are common (e.g. Firth & Sheldon, 2016; Mourier et al, 2019; O'Brien et al., 2018), these relationships vary considerably across systems, and can be context‐dependent (e.g. O'Brien et al., 2018).…”

CMRnet: An r package to derive networks of social interactions and movement from mark–recapture data

“…The social structure of populations is critical in shaping key ecological processes, such as the spread of information and infections (Allen et al., 2013; Aplin et al., 2015; White et al., 2017), and in driving patterns of evolutionary change (Fisher & McAdam, 2017). On the one hand, social relationships will be influenced by demographic changes; for example, individuals may interact more with others at higher population densities (O'Brien et al., 2018). On the other hand, social relationships may influence key demographic processes, such as reproductive rates (McDonald, 2007), dispersal (Blumstein et al., 2009) or survival (Ellis et al., 2017).…”