Positive associations among rare species and their persistence in ecological assemblages

Abstract

According to the competitive exclusion principle, species with low competitive abilities should be excluded by more efficient competitors; yet, they generally remain as rare species. Here, we describe the positive and negative spatial association net- works of 326 disparate assemblages, showing a general orga- nization pattern that simultaneously supports the primacy of competition and the persistence of rare species. Abundant species monopolize negative associations in about 90% of the assemblages. On the other hand, rare species are mostly involved in positive associations, forming small network mod- ules. Simulations suggest that positive interactions among rare species and microhabitat preferences are the most prob- able mechanisms underpinning this pattern and rare species persistence. The consistent results across taxa and geography suggest a general explanation for the maintenance of biodi- versity in competitive environments.