Contrasting species functional trait structuring of subarctic versus subtropical copepod communities

• Published in: bioRxiv
• Main Authors: García-Comas, Carmen, Hsieh, Chih-Hao, Chiba, Sanae, Sugisaki, Hiroya, Hashioka, Taketo, Sherwood Lan Smith
• Format: Paper
• Language: English
• Published: Cold Spring Harbor Cold Spring Harbor Laboratory Press 01.02.2020
• Subjects: Community; Niches; Reproductive fitness; Species
• DOI: 10.1101/2020.01.31.928705

Classic niche theory assumes that species-level functional traits affect species relative fitness and thus community structuring, but empirical tests of this assumption are scarce. Moreover, recent evidence shows increasing functional over-redundancy towards the tropics, suggesting that the extent to which functional traits confer species' fitness and thus impact community structuring differs across latitudes. Here, we develop a new method: comparing the frequencies of trait categories in the species-rank abundance distributions of local communities versus their frequencies in the regional average species pool. We contrasted subarctic versus subtropical copepod communities for six important traits. In subarctic communities, medium-sized and cold-water species are selected to dominate, thus traits affect relative fitness as predicted by classic niche theory. In subtropical communities, most species are small and warm-water, but these categories are not selected to dominate, suggesting that greater diversity towards the tropics results from lesser trait-based fitness differences allowing more species to coexist.