Consistency in defence and competitiveness trade-off in a planktonic predator-prey system

Abstract

AbstractPredator-prey interactions play a central role in community dynamics and thus energy and matter transfers in food webs. Intraspecific variation in traits and particularly in trait combinations involved in trade-offs can alter predator-prey interactions but the underlying mechanisms governing these interactions are still unclear. Quantifying the relevant traits forming trade-off relationships and how these traits determine prey and predator fitness remains a major challenge, even for a single species. Here, we measured multiple traits related to defensive and competitive abilities to investigate the intraspecific trade-off between defence and competitiveness in 6 different strains of the green alga Chlamydomonas reinhardtii exposed to predation by the rotifer Brachionus calyciflorus and examine the consistency of the trait relationships and its consequence for the predator.We found significant differences in defence and competitiveness traits that were used to categorized prey strains as defended against predation and poor competitors, undefended against predation and good competitors, or intermediate in both traits. Furthermore, we found that the different morphological and trophic traits related to defence and competitiveness of prey strains were negatively correlated. The position of prey strains in trait space were consistent independent of the defence and competitiveness trait considered. As we compared trait differences between prey strains coming from environments where selection has favoured one trait or the other, these negative correlations strongly suggested the presence of a trade-off between defence and competitiveness.Our study represents the first empirical evidence of the consistency in the expression of a defence-competitiveness trade-off at the intraspecific level. Assessing the relation between relevant traits and trade-offs and understanding how it translates into fitness of prey and predator allows improving general theory on the outcomes of predator-prey interactions and ecosystem processes.