Interactive Effects Of Food C:P Ratios And Temperature Rising On The Life History And Population Growth Of Daphnia Magna

The growth and reproduction of consumers are usually regulated by food quality(stoichiometric food quality,etc.),which can further affects their population dynamics and some important ecological functioning.Meanwhile,temperature is of primary importance in determining the population growth and metabolism rate of ectothermic organisms.However,it is still not well-documented how food quality affects the life history and population growth responses of consumers to higher temperature in the future warming.In this study,we examined the life history traits,population growth rates,feeding rate and body elemental contents of Daphnia manna exposed to widely variable food carbon : phosphorus(C:P)ratios across two different temperatures(25 ℃ and 29°C).Furthermore,we then tested those results from indoor simulated experiments based on a simulated field system study.The main results are as follows:1.Stoichiometric food quality and temperature rising have a significant interactive effect on life-history traits and population growth of the D.magna(df = 9,P <0.01).The growth,reproduction and population growth rates were significantly affected by food C:P ratios,and the greatest proportional effect was observed at food C:P ratio of 868.Additionally,temperature rising is not conducive to the life-history traits and population growth.The negative effects of food C:P ratio on the life-history traits and population growth of D.magna were enhanced by the higher temperature.2.The feeding rate of D.magna decreased significantly with the increase of food C:P ratios and temperature.The feeding rate of higher food C:P ratio was 44.3% lower than that of low food C:P ratio at temperature of 25℃.Meanwhile,we suggested temperature significantly reduced the feeding rate of D.magna.These effects may reflect the higher temperature can reduce feeding rate constraints associated with food P content in D.magna.3.Stoichiometric food quality and temperature had significant interactive effects on body C and N contents of D.magna(%C: df = 9,P < 0.01;%N: df = 9,P < 0.01).There were significantly negative correlation between D.magna body %C and %P and food C:P ratio at higher temperature,revealing that the response of D.magna body %C and %P to the C:P ratio of food is affected by temperature.However,little significant effect was observed on body element content of D.magna by temperature.4.In simulated field experiments,we also observed a significant interactive effect of food C:P ratios and temperature rising on the life-history parameters,population growth,and feeding rate of D.magna(df = 9,P < 0.01).However,there was no a significant effect of food C:P ratio on body element content of D.magna,while higher temperature significantly reduced the P content of D.magna(df = 1,P < 0.05).In summary,our findings highlight that temperature can change the response of D.magna to the stoichiometric food quality.Elevated temperature increases the risk of food P-limitation for life history traits and population growth in D.magna.These experiments may help us to understand the consequences of complicate effects of anthropogenic perturbations in nutrients and phosphorus for consumer nutrition under future climate warming scenario.