Does the stoichiometric carbon:phosphorus knife edge apply for predaceous copepods?

CECILIA LASPOUMADERES; BEATRIZ MODENUTTI; JAMES ELSER; ESTEBAN BALSEIRO

OECOLOGIA

SPRINGER

Lugar: Berlin; Año: 2015 vol. 178 p. 557 - 569

0029-8549

Recent work has indicated that stoichiometric food quality in terms of carbon:phosphorus (C:P) ratios affects consumers whether the imbalance involves a deficit or an excess of nutrients; hence, organisms exist on a ?stoichiometric knife edge?. While previous studies have focused primarily on autotroph-herbivore trophic transfer, nutritional imbalances might also affect the interactions between species at higher trophic levels. Since the foods of carnivores are normally stoichiometrically similar to their own body composition, they may be more severely affected than herbivores if imbalances do become pronounced. We analysed the response of the predatory copepod Parabroteas sarsi to monospecific diet treatments consisting of high and low C:P prey items. These dietary treatments strongly affected the predators? elemental composition and growth, although prey selection, excretion, egestion, and respiration rates were not affected. We suggest that, due to their low threshold elemental ratio and a narrow C:P stoichiometric knife edge, these predators are highly vulnerable to stoichiometric imbalances, whether an excess or a deficit of nutrients is involved. Our results demonstrating this high sensitivity to prey C:P ratio show that the stoichiometric knife edge may apply not only to herbivores but also to higher trophic levels. Thus, predators such as P. sarsi, with a much narrower food quality range, may also be strongly affected by fluctuations in the quality of their prey, with negative consequences for their secondary production.