Effect of circadian cycle and prey density on the demography of the predator Asplanchna silvestrii (Rotifera)

Abstract

We studied the demographic responses (average lifespan (ALS), gross reproductive rate (GRR), net reproductive rate (NRR), generation time (GT) and the rate of population increase per day (r) of the predatory rotifer A. silvestrii cultured under five different durations of light conditions (L:D ¼ 24:0, 18:6, 12:12, 6:18, and 0:24 in a 24 h cycle) and under two prey (Plationus patulus) densities (0.5 and 5.0 ind. mL À1 ). Our data showed that regardless of prey density, the survivorship of A. silvestrii was affected by the duration of photoperiod; the longest ALS was under complete darkness. For any given prey density, lowest GRR was recorded at 24L:0D. The NRR was lower under continuous light (24L:0D) regime. The longest GT was recorded when Asplanchna silvestrii was fed on high prey density and under total dark regime. The r ranged from 0.15 (24L:0D photoperiod in low prey density) to 0.6 day À1 (18L:6D and high prey density) and for the rest of treatments, the values remained within this range.