Abstract
Primary consumers in aquatic ecosystems are frequently limited by the
quality of their food, often expressed as phytoplankton elemental and
biochemical composition. Effects of these food quality indicators vary
across studies, and the relative importance of elemental (nitrogen and
phosphorus) versus biochemical (fatty acid and sterol) limitation in
aquatic food webs has been debated. Here we present results of a
meta-analysis using >100 experimental studies, which
confirms that limitation by N, P, essential fatty acids, and sterols all
have significant negative effects on zooplankton performance. However,
effects varied by grazer response (growth versus reproduction), specific
manipulation, and across taxa. P limitation had greater effects on
zooplankton growth than fatty acids, but P and fatty acid limitation had
equal effects on reproduction. Furthermore, we show that nutrient
co-limitation in zooplankton occurs, that indirect effects induced by P
limitation exceed direct effects of mineral P limitation, that effects
of nutrient amendments using laboratory phytoplankton isolates exceed
those using natural field communities, and that algal physiology
mediates zooplankton responses to nutrient limitation. Our meta-analysis
reconciles contrasting views about the role of various food quality
indicators, and their interactions, for zooplankton performance, and
provides a mechanistic understanding of how environmental change affects
trophic transfer.