TY - JOUR A1 - Lukas, Marcus A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Growth Rate Hypothesis does not apply across colimiting conditions cholesterol limitation affects phosphorus homoeostasis of an aquatic herbivore JF - Functional ecology : an official journal of the British Ecological Society N2 - 1. Herbivores show stronger control of element homoeostasis than primary producers, which can lead to constraints in carbon and nutrient transfer efficiencies from plants to animals. Insufficient dietary phosphorus (P) availability can cause reduced body P contents along with lower growth rates of animals, leading to a positive relationship between growth and body P. 2. We examined how a second limiting food component in combination with dietary P limitation influences growth and P homoeostasis of a herbivore and how this colimitation influences the hypothesized positive correlation between body P content and growth rates. Therefore, we investigated the responses in somatic growth and P stoichiometry of Daphnia magna raised on a range of diets with different amounts of P and the sterol cholesterol. 3. Somatic growth rates of D. magna increased asymptotically with increasing P as well as with increasing cholesterol availability. The body P content increased with increasing dietary P and stabilized at high dietary P availability. The observed plasticity in D. magna's P stoichiometry became stronger with increasing cholesterol availability, i.e. with decreasing colimitation by cholesterol. 4. At P-limiting conditions, the positive correlation between body P content and growth rate, as predicted by the growth rate hypothesis (GRH) applied to the within-species level, declined with increasing cholesterol limitation and disappeared entirely when cholesterol was not supplied. Thus, even when Daphnia shows no growth response owing to strong limitation by the colimiting nutrient, the body P content may vary substantially, calling into question the unconditional use of herbivores' P content as predictor of a potential P limitation in nature. 5. The observed interaction between dietary P and cholesterol on Daphnia's growth and stoichiometry can be used as a conceptual framework of how colimiting essential nutrients affect herbivore homoeostasis, and provide further insights into the applicability of the GRH within a consumer species. KW - colimitation KW - Daphnia KW - ecological stoichiometry KW - essential resources KW - food quality KW - imbalanced diet KW - nutrient limitation KW - nutritional ecology KW - zooplankton Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2435.2011.01876.x SN - 0269-8463 VL - 25 IS - 6 SP - 1206 EP - 1214 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Sperfeld, Erik A1 - Martin-Creuzburg, Dominik A1 - Wacker, Alexander T1 - Multiple resource limitation theory applied to herbivorous consumers Liebig's minimum rule vs. interactive co-limitation JF - Ecology letters N2 - There is growing consensus that the growth of herbivorous consumers is frequently limited by more than one nutrient simultaneously. This understanding, however, is based primarily on theoretical considerations and the applicability of existing concepts of co-limitation has rarely been tested experimentally. Here, we assessed the suitability of two contrasting concepts of resource limitation, i.e. Liebigs minimum rule and the multiple limitation hypothesis, to describe nutrient-dependent growth responses of a freshwater herbivore (Daphnia magna) in a system with two potentially limiting nutrients (cholesterol and eicosapentaenoic acid). The results indicated that these essential nutrients interact, and do not strictly follow Liebigs minimum rule, which consistently overestimates growth at co-limiting conditions and thus is not applicable to describe multiple nutrient limitation of herbivorous consumers. We infer that the outcome of resource-based modelling approaches assessing herbivore population dynamics strongly depends on the applied concept of co-limitation. KW - Cholesterol KW - Daphnia magna KW - eicosapentaenoic acid KW - essential resources KW - food quality KW - herbivore KW - multi-nutrient limitation KW - nutritional ecology KW - von Liebig Y1 - 2012 U6 - https://doi.org/10.1111/j.1461-0248.2011.01719.x SN - 1461-023X VL - 15 IS - 2 SP - 142 EP - 150 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Temperature affects the limitation of Daphnia magna by eicosapentaenoic acid, and the fatty acid composition of body tissue and eggs JF - Freshwater biology N2 - 1. Poikilothermic animals incorporate more polyunsaturated fatty acids (PUFAs) into their cellular membranes as temperature declines, suggesting an increased sensitivity to PUFA limitation in cool conditions. To test this we raised Daphnia magna at different temperatures and investigated the effect of varying dietary PUFA on life history parameters (i.e. growth, reproduction) and the PUFA composition of body tissue and eggs. 2. Upon a PUFA-rich diet (Cryptomonas sp.) females showed higher concentrations of several omega 3 PUFAs in their body tissue at 15 degrees C than at 20 degrees C and 25 degrees C, indicating a greater structural requirement for omega 3 PUFAs at low temperature. Their eggs had an equal but higher concentration of omega 3 PUFAs than their body tissue. 3. In a life history experiment at 15 and 20 degrees C we supplemented a diet of a PUFA-free cyanobacterium with the omega 3 PUFA eicosapentaenoic acid (EPA). The growth of D. magna was more strongly EPA limited at low temperature. A greater requirement for structural EPA at 15 degrees C was indicated by a steeper increase in somatic EPA content with dietary EPA compared to 20 degrees C. 4. At 20 degrees C the development of eggs to successful hatching was high when EPA was supplied to the mothers. At 15 degrees C the hatching success was generally poor, despite of a higher maternal provision of EPA to eggs, compared to that at 20 degrees C, suggesting that EPA alone was insufficient for proper neonatal development at the low temperature. The growth of offspring from mothers raised at 20 degrees C without EPA supplementation was very low, indicating that the negative effects of EPA deficiency can be carried on to the next generation. 5. The fatty acid composition of Daphnia sp. in published field studies shows increasing proportions of saturated fatty acids with increasing environmental temperature, whereas omega 3 PUFAs and EPA show no clear pattern, suggesting that variations in dietary PUFA may mask temperature-dependent adjustments in omega 3 PUFA concentrations of cladocerans in nature. KW - food quality KW - maternal effects KW - polyunsaturated fatty acids KW - resource allocation KW - zooplankton Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2427.2011.02719.x SN - 0046-5070 VL - 57 IS - 3 SP - 497 EP - 508 PB - Wiley-Blackwell CY - Hoboken ER -