The Strength of Nocomis Nest Association Contributes to Patterns of Rarity and Commonness among New River, Virginia Cyprinids

Many North American minnows (Cyprinidae) exhibit nest association, a spawning mode in which one species (associate) uses nests constructed by another species (host). Although this relationship may be obligate for some species, many nest associates can use alternative reproductive modes, indicating that the strength of the relationship between associate and host may vary. Quantifying the strength of the nest association relationship represents a necessary first step for understanding the importance of this interaction to stream fish communities. To address this question, we conducted a literature review of ecological and ethological reproductive traits for 11 nest associates of Nocomis occurring in the New River basin, Virginia. We used phylogenetic eigenvector regression (PVR) to remove the effects of phylogenetic relatedness among species and used nonmetric multidimensional scaling (NMS) to ordinate a phylogenetically independent trait similarity matrix of the 11 species. Based on the ordination results, we delineated a group of strong and weak nest associates. Strong nest associates showed significant geographic range overlap with Nocomis, while weak ones did not. No difference in spawning temperature range overlap occurred between the two groups. We then tested for effects of nest association strength on species' rarity and found that most (6 of 7) strong nest associates held rare classifications based on one or more of geographic extent, habitat breadth, or local abundance. Conversely, all weak nest associates reflected common classifications. These results indicate that nest association strength is related to rarity; this potentially crucial aspect of conservation has been previously overlooked. Clearly, conservation of rare and imperiled nest associates should be pursued through protection of their host and, consequently, the mutualism they have evolved to exploit.