Influence of prey availability, visual contrast and size of dragonfly (Pantala sp.) larvae (Odonata, Insecta) on the predation of <em>Simocephalus serrulatus</em> (Cladocera, Crustacea)

Abstract

The influence of prey availability, visual contrast and size of dragonfly (Pantala sp) larvae on the predation of cladocerans (Simocephalus serrulatus) is provided. Twenty-four dragonfly naiads (12.57±0.05 mm and 100.01±9.16 mg) were employed to study the relation between predation rate and availability of cladocerans and visual contrast. 5,10, 15 and 20 cladocerans/L were placed in 1L transparent and black plastic lined aquariums. Cladocerans (1.63±0.21 mm and 0.78 mg) were counted and replaced hourly for five consecutive hours. Twenty-four naiads of different sizes were placed in 50mL recipients to study effects of size of dragonfly larvae. Each larvae received 20 cladocerans; counting and reposition of individuals consumed every ten minutes during two consecutive hours were undertaken. Quadratic effect (p < 0.02) in predation rate was reported, with an increase in prey availability: 21.67; 39.00; 42.44 and 49.67% were reported for densities of 5, 10, 15 and 20 cladocerans/L respectively. Predation rate (p < 0.02) was higher in dark wall aquariums (42.67%) than in those with transparent walls (33.72%). Size of dragonfly larvae had a quadratic effect on the predation of cladocerans and highest value occurred with 13.23 mm naiads. While high prey availability increases predation rate, predation is higher in aquariums with dark walls and 13.23 mm-long larvae have the highest predation rate