Vertical Transmission of Social Roles Drives Resilience to Poaching in Elephant Networks

Abstract

Network resilience to perturbation is fundamental to functionality in systems ranging from synthetic communication networks to evolved social organization [1]. While theoretical work offers insight into causes of network robustness, examination of natural networks can identify evolved mechanisms of resilience and how they are related to the selective pressures driving structure. Female African elephants (Loxodonta africana) exhibit complex social networks with node heterogeneity in which older individuals serve as connectivity hubs [2, 3]. Recent ivory poaching targeting older elephants in a well-studied population has mirrored the targeted removal of highly connected nodes in the theoretical literature that leads to structural collapse [4, 5]. Here we tested the response of this natural network to selective knockouts. We find that the hierarchical network topology characteristic of elephant societies was highly conserved across the 16-year study despite ∼70% turnover in individual composition of the population. At a population level, the oldest available individuals persisted to fill socially central positions in the network. For analyses using known mother-daughter pairs, social positions of daughters during the disrupted period were predicted by those of their mothers in years prior, were unrelated to individual histories of family mortality, and were actively built. As such, daughters replicated the social network roles of their mothers, driving the observed network resilience. Our study provides a rare bridge between network theory and an evolved system, demonstrating social redundancy to be the mechanism by which resilience to perturbation occurred in this socially advanced species.

Wild birds respond to flockmate loss by increasing their social network associations to others

“…For example, a recent observational study indicated that wild African elephant ( Loxodonta africana ) populations maintain their social network structure, despite ivory poaching eliminating the highly connected nodes (i.e. older female elephants) [58]. While no active response to such loss was exhibited, the robustness instead stemmed from daughters replicating their mothers' social positions.…”

Hunting promotes spatial reorganization and sexually selected infanticide

“…Spatial and social relationships of bears are likely to change more rapidly in areas with higher hunting mortality, thereby potentially decreasing the cohesion of their social network2829 but see ref. 30. Such effects could also influence the female reproductive rate because female brown bears exhibit kin-related spatial structures31, where neighbors negatively affect each other’s probability of having cubs3233.…”

Human‐driven habitat conversion is a more immediate threat to Amboseli elephants than climate change

“…Movement decisions are guided not only by food availability, but also by perceived risks (Graham, Douglas-Hamilton, Adams, & Lee, 2009), water availability (Chamaillé-Jammes et al, 2009, and social companions (Goldenberg, Douglas-Hamilton, & Wittemyer, 2016), among other factors. Rather, elephants utilize established home ranges and move seasonally to maximize resource availability.…”