Long‐term changes in intra‐ and interspecific trait variability of a small herbivore in a deep perialpine lake

Analyses of trait dynamics provide new insights into the dynamics of communities and ecosystems. While zooplankton traits—and especially the defensive traits—of zooplankton are well studied in the laboratory, there are hardly any studies analyzing long‐term dynamics of zooplankton traits. Here, we study species turnover and trait dynamics of three species of the genus Bosmina, Bosmina coregoni, Bosmina longispina, and Bosmina longirostris, at the genus and species levels during three decades of environmental changes in Lake Constance. We showed that Bosmina species turnover substantially influenced genus‐level body size distributions and key defensive traits, including mucro and antennule sizes. Results also showed that mean species traits more effectively predicted genus‐level traits when interspecies trait differences were large, making them particularly reliable in species‐rich contexts. In contrast, when trait differences among species were small, intraspecific variations may obscure genus‐level temporal patterns. In addition, we found within‐species trait changes that partially paralleled those observed at the genus level, but also within‐species trait changes that partially differed from those observed at the genus level. While a large reduction of nutrients during two decades appeared not to be strongly associated with changes in Bosmina species composition and trait dynamics, large and rapid species turnover and trait changes coincided with 7 yr of increased stickleback densities in the pelagic zone of the lake.