Do persistent rare species experience stronger negative frequency dependence than common species?

Understanding why so many species are rare yet persistent remains a significant challenge for both theoretical and empirical ecologists. Yenni, Adler, and Ernest (2012) proposed that strong negative frequency dependence causes species to be rare while simultaneously buffering them against extinction. This hypothesis predicts that, on average, rare species should experience stronger negative frequency dependence than common species. However, it is unknown if ecological communities generally show this theoretical pattern, or if rarity is primarily determined by other processes that overwhelm the effects of strong negative frequency dependence. We discuss the implications of this mechanism for natural communities, and develop a method to test for a non-random relationship between negative frequency dependence and relative abundance, using species abundance data from 90 communities across a broad range of environments and taxonomic groups. To account for biases introduced by measurement error, we compared the observed correlation between species relative abundance and the strength of frequency dependence against expectations from a randomization procedure. In approximately half of the analyzed communities, rare species showed disproportionately strong negative frequency dependence compared to common species. Specifically, we found a pattern of increasingly strong negative frequency dependence with decreasing relative abundance. Our results suggest that strong negative frequency dependence is a signature of both rarity and persistence for many species in many communities.