Functional responses describe the per capita consumption rates of predators depending on prey density, thus quantifying the energy transfer between trophic levels. According to Holling’s disk equation, functional responses are described by handling time and attack rate. The aim of our study was to investigate how these parameters depend on predator-prey body-mass ratios and temperature. We studied allometric functional responses of the most abundant ground dwelling predators of different body masses (carabid beetles, lycosid spiders and chilopodes) that dominate many forest litter communities in central Europe. Two prey species of different body masses were offered to each predator: Drosophila hydei (Diptera) and Heteromurus nitidus (Collembola) were offered to lycosid spiders and chilopodes, Alphithobius diapernus (Coleoptera) and Drosophila hydei (Diptera) were offered to carabid beetles. These experiments were carried out at a temperature of 15°C.
Furthermore, we studied how the parameters of the functional response depend on temperature. We measured the functional responses of three different sized carabid beetles at six different temperatures (5°, 10°, 15°, 20°, 25° and 30°C), offering again A. diapernus (Coleoptera) and D. hydei (Diptera) as prey.
Results/Conclusions
The results of the allometric functional response experiments showed that successful attack rates increased with increasing predator-prey body-mass ratios. They reached a maximum at intermediate body-mass ratios and decreased towards high and low body-mass ratios. The handling time decreased with increasing predator-prey body-mass ratio.
In the temperature experiment, the handling time decreased with increasing temperature leading to an increase of the maximum ingestion rate with increasing temperature. In contrast to the allometric functional response experiments, we found no significant impact of temperature on the attack rates. Using these systematically parameterized functional responses allows modelling population dynamics by relating the functional response of the predator to the predator-prey body-mass ratio and the environmental temperature.
