Strength of a Social Network of Blacktip Reef Sharks
http://rsbl.royalsocietypublishing.org.proxy.library.cornell.edu/content/13/3/20160824
In a study published in Biology Letters in March 2017, Dr. Johann Mourier and his colleagues studied the connectivity of a population of blacktip reef sharks in French Polynesia and the importance of nodes to this social network of sharks. Over a two-year period, they took photos of sharks they saw on dives and inferred edges between sharks based on how long and how spatially close they were together. They also recorded connections between sharks if they observed social behaviors. The researchers also quantified the connectivity of different sharks by using statistical analysis of: “dyadic associations” (having an edge between two sharks/nodes), “betweenness centrality” (node’s importance as part of a bridge/local bridge), and “node degree” (number of edges to a node) (Mourier). With this data, they made a computer model and investigated the effects of node removals from the network. With each node removal, they counted how many shark nodes were in the largest component of the population. The results of this study showed that the sharks’ social network was pretty connected even with the removal of “more than 25%” of the nodes (Mourier). They concluded that the fishing of sharks would not significantly disrupt the social network of this group of sharks.
This academic paper is relevant to our class because the social network analysis of these sharks showed that these sharks had a highly connected social network. The sharks represented the nodes of the social network and the edges were the social relationships between them. The researchers also found that sharks tend to be linked to individuals similar to each other. Additionally, the high connectivity of the social network implies that the strong triadic closure property is in effect within this population. Taking into account the behavior of sharks, it is likely that a shark that had strong ties to two other sharks would benefit from those two being at least weakly connected. For example, if they were all hunting together, it would be better that all three sharks had some sort of connection so they could work together well and not fight over food. Furthermore, this shark population mated in the same place annually; if the three sharks were all connected to each other, they would not have to worry about aggression from the sharks they were connected to while mating. In addition, we discussed components of a social network in class. The researchers found that it took a large amount of node removal to decrease the size of the largest component in the shark’s social network. In conclusion, this paper demonstrated that certain species of sharks have complex social networks similar to the human or human-created networks we have studied in class.