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

LASPOUMADERES, C., ; MODENUTTI, B.,; ELSER, J.J. .; BALSEIRO, E.

OECOLOGIA

SPRINGER

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

0029-8549

Recent work has indicated that stoichiometric food quality in terms ofcarbon:phosphorus (C:P) ratios affects consumers whether the imbalance involves adeficit or an excess of nutrients; hence, organisms exist on a "stoichiometric knifeedge". While previous studies have focused primarily on autotroph-herbivore trophictransfer, nutritional imbalances might also affect the interactions between species athigher trophic levels. Since the foods of carnivores are normally stoichiometricallysimilar to their own body composition, they may be more severely affected thanherbivores if imbalances do become pronounced. We analysed the response of thepredatory copepod Parabroteas sarsi to monospecific diet treatments consisting ofhigh and low C:P prey items. These dietary treatments strongly affected the predators´elemental composition and growth, although prey selection, excretion, egestion, andrespiration rates were not affected. We suggest that, due to their low thresholdelemental ratio and a narrow C:P stoichiometric knife edge, these predators are highlyvulnerable to stoichiometric imbalances, whether an excess or a deficit of nutrients isinvolved. Our results demonstrating this high sensitivity to prey C:P ratio show that thestoichiometric knife edge may apply not only to herbivores but also to higher trophiclevels. Thus, predators such as P. sarsi, with a much narrower food quality range, mayalso be strongly affected by fluctuations in the quality of their prey, with negativeconsequences for their secondary production.