Interspecific competition underlying mutualistic networks

The architecture of bipartite networks linking two classes of constituents is affected by the interactions within each class. For the bipartite networks representing the mutualistic relationship between pollinating animals and plants, it has been known that their degree distributions are broad but often deviate from power-law form, more significantly for plants than animals. Here we consider a model for the evolution of the mutualistic networks and find that their topology is strongly dependent on the asymmetry and non-linearity of the preferential selection of mutualistic partners. Real-world mutualistic networks analyzed in the framework of the model show that a new animal species determines its partners not only by their attractiveness but also as a result of the competition with pre-existing animals, which leads to the stretched-exponential degree distributions of plant species.

💡 Research Summary

The paper investigates how intra‑class interactions shape the architecture of bipartite mutualistic networks, focusing on pollinator–plant systems. While previous studies have reported broad degree distributions for both animals and plants, empirical data often show that plant degree distributions deviate from pure power‑law behavior, tending toward stretched‑exponential or exponential tails. To explain this asymmetry, the authors extend the classic preferential attachment framework by introducing two key modifications: (1) a non‑linear preferential selection of partners, characterized by an exponent α that governs how strongly a plant’s current degree influences its attractiveness; and (2) a competition‑mediated suppression term, parameterized by β, that captures the effect of existing animal species on the probability that a newcomer will attach to a given plant. The attachment probability for a new animal i to a plant j is expressed as

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