Comparison of copepod species-based and individual-size-based community structuring

Abstract

Functional trait studies are proliferating in plankton ecology, especially studies analysing body size. Yet, empirical studies comparing species versus individual-size structuring are scarce. Here, we conducted a comparison of copepod species-based and individual-size-based community structuring in the East China Sea, and found that: (i) Species, species-based nominal-size and individual-size distributions exhibit very different patterns, and that juveniles (neglected in species counts due to limitation of recognition) tend to dominate in a certain size range. (ii) Species-based structuring is more strongly shaped by physical conditions, while individual-size-based structuring is more strongly shaped by food availability. (iii) Despite these differences, the congruence (i.e. degree of match) between species-based and individual-size-based structuring remains statistically significant. Finally, we tested intrinsic factors potentially explaining the degree of mismatch (i.e. species richness and proxies for: size partitioning of species without accounting for intraspecific variability, intraspecific variability without accounting for ontogeny and ontogeny). (iv) The frequency of juveniles (proxy for ontogeny) is the only intrinsic factor significantly explaining the mismatch between species and size structuring, highlighting the problem of the classic species-based analysis that unavoidably neglects juveniles in the species counts. These results support individual-size as a useful complementary descriptor to species-based studies.