  On Reddit, individual subreddits are used to organize content and connect
users. One mode of interaction is the subreddit link, which occurs when a user
makes a direct reference to a subreddit in another community. Based on the
ubiquity of these references, we have undertaken a study on subreddit links on
Reddit, with the goal of understanding their impact on both the referenced
subreddit, and on the subreddit landscape as a whole. By way of an extensive
observational study along with several natural experiments using the entire
history of Reddit, we were able to determine that (1) subreddit links are a
significant driver of new suberddit creation; (2) subreddit links (2a)
substantially drive activity in the referenced subreddit, and (2b) are
frequently created in response to high levels of activity in the referenced
subreddit; and (3) the graph of subreddit links has become less dense and more
treelike over time. We conclude with a discussion of how these results confirm,
add to, and in some cases conflict with existing theories on
information-seeking behavior and self-organizing behavior in online social
systems.
