Predicting fate from early connectivity in a social network

Abstract

In the long-tailed manakin (Chiroxiphia linearis), a long-lived tropical bird, early connectivity within a social network predicts male success an average of 4.8 years later. Long-tailed manakins have an unusual lek mating system in which pairs of unrelated males, at the top of complex overlapping teams of as many as 15 males, cooperate for obligate dual-male song and dance courtship displays. For as long as 8 years before forming stable "alpha-beta" partnerships, males interact with many other males in complex, temporally dynamic social networks. "Information centrality" is a network connectivity metric that accounts for indirect as well as shortest (geodesic) paths among interactors. The odds that males would rise socially rose by a factor of five for each one-unit increase in their early information centrality. Connectivity of males destined to rise did not change over time but increased in males that failed to rise socially. The results suggest that network connectivity is important for young males (ages 1-6) but less so for older males of high status (ages 10-15) and that it is difficult to explain present success without reference to social history.

Fig. 1.

Social networks in long-tailed manakins. (Left Top–Bottom and Right Top and Middle) Subnetworks in successive 2-year timeblocks. (Right Bottom) The cumulative network (1989–1998) for 95 males and 61 females. Early connectivity, assessed by the network metric information centrality, predicts later fate. Circles (nodes), colored by category, represent individuals, and lines (undirected, unweighted links) represent social interactions at lek display perches. Node size (males only) represents information centrality, which is defined in the text. In Left Top–Bottom and Right Top and Middle, node size represents information centrality relative to males of the same category in that subnetwork. In Right Bottom, node size represents information centrality in each male's last timeblock adjusted by the mean in that subnetwork. White symbols (X, triangle, asterisk, and enclosed or enclosing square) track four individual males through time. Note that, as successful alphas (Right Bottom), all four tracked males had moderate information centrality. The number of banded females linked to alpha males is a reasonable proxy for male mating success.

Fig. 2.

Logistic regression for binary rise in success (response) as a function of information centrality (predictor) in long-tailed manakin social networks. Early connectivity predicted fate (social rise) 4.8 years later on average. A male's information centrality score was relative to that of others in the same category for the 2-year timeblock (Fig. 1) in which he was first seen interacting. Curve plots probability of success as a function of information centrality (logit[p] = −1.21 + 1.6 × information centrality). Points are response averages binned in groups of 10 (±SE). A male's odds of later social rise were 4.96 times higher for each unit increase in his relative information centrality (scale 0–2). In contrast, information centrality in the final timeblock subnetwork was not correlated with contemporaneous success.