Identifying Competition and Mutualism Between Online Groups

TL;DR

This work shows that treating overlapping online groups as a single environmental niche can obscure the diversity of intergroup relationships. By contrasting population-ecology density-dependence with a new community-ecology approach that infers directed competition and mutualism networks from time-series data, the authors demonstrate that most interactions within closely related subreddit clusters are mutualistic. They introduce a VAR-based framework to estimate a community matrix $\mathbf{\Phi}$, compute impulse responses, and quantify overall interaction strength $\kappa$ and mean mutualism $\overline{m}$, revealing a predominance of mutualism across clusters. The findings improve short-horizon forecasting when ecological interactions are modeled and offer a foundation for designing online communities that leverage intergroup complementarities. The approach complements existing population-ecology results and provides actionable insight for platform designers seeking to foster healthy, interconnected online ecosystems.

Abstract

Platforms often host multiple online groups with overlapping topics and members. How can researchers and designers understand how related groups affect each other? Inspired by population ecology, prior research in social computing and human-computer interaction has studied related groups by correlating group size with degrees of overlap in content and membership, but has produced puzzling results: overlap is associated with competition in some contexts but with mutualism in others. We suggest that this inconsistency results from aggregating intergroup relationships into an overall environmental effect that obscures the diversity of competition and mutualism among related groups. Drawing on the framework of community ecology, we introduce a time-series method for inferring competition and mutualism. We then use this framework to inform a large-scale analysis of clusters of subreddits that all have high user overlap. We find that mutualism is more common than competition.

Figures (6)

• Figure 1: A 2D histogram of subreddits with overlap density (log-transformed) on the X-axis and the change in the logarithm of the number of distinct commenting users on the Y-axis. The black line shows the marginal effect of overlap density on growth as predicted by Model 2. The gray region shows the 95% confidence interval of the marginal effect.
• Figure 2: Two-dimensional histogram showing ecological communities on Reddit in our typology. The X-axis shows the overall degree of mutualism or competition in clusters of subreddits with high user overlap based on the average ecological interaction. The Y-axis shows the ecological interaction strength representing the overall magnitude of competition or mutualism.
• Figure 3: The ecological community of subreddits for supporting mental health and survivors of abuse is dense with largely mutualistic interactions.
• Figure 4: The subreddits about real estate and finance are relatively competitive.
• Figure 5: Subreddits about watches are dense with both mutualistic and competitive interactions.