Trait-density relationships explain performance in cladoceran zooplankton.

Traits have been used extensively to predict and understand performance in response to the abiotic environment, but their role for understanding competitive interactions is less understood, especially in nonplant systems. In this study, we evaluate how traits interact with intraspecific density to modulate performance (per capita birth rate) and whether the traits associated with intraspecific competitive ability are similar across multiple species. We used an experimental system of four cladoceran zooplankton species, experimentally manipulated the density of conspecifics, and measured a range of morphological and life history characteristics (body mass, body length, second antenna length, eye diameter, relative growth rate, age at first reproduction, and birth rate).