The comprehensive effect of natural food quality and quantity on growth rate of herbivore consumers

Abstract

The performance of herbivore consumers in freshwater ecosystems is influenced by food quality and quantity, which are crucial factors in understanding energy flow. However, the comprehensive effects of these factors on consumer growth based on natural food research remain unclear. To address this gap, we conducted a growth experiment culturing the Cladocera Daphnia similis in natural lake water collected from 30 subtropical lakes. Our results showed that the seston concentration (SC), seston phosphorus (seston P), and seston carbon: phosphorus ratio (seston C:P, in moles) were the most important factors in influencing the growth rate of D. similis according to the Random Forest model. Specifically, the growth rate of D. similis was significantly positive correlated with SC and seston P, and significantly negative correlated with seston C:P. D. similis exhibited the optimal growth performance within the seston C:P range of 32.8 to 69.8, with a sharp decline in growth rate observed at a break point of seston C:P of 70. The combined effect of food quality and quantity on growth rate was that higher SC (≥0.26 mg C/L), lower seston C:P (≤69.80), and higher P (≥0.11 mmol/g) were associated with significantly higher growth rates. Additionally, the growth rate increased significantly with the biomass of cryptophyte, indicating the importance of food composition. Our study shows that the growth rate of D. similis is co-affected by the quality and quantity of natural food. SC, seston C:P, seston P and algae composition are reliable indicators for assessing the growth rate of consumer in freshwater ecosystems. The inhibitory effect of low C:P on consumer growth should be applied with caution when assessing the development of herbivore consumers in natural lakes.