DIEL PATTERN OF PREDATION RISK IN MICROTINE RODENTS

By reviewing information about the activity behaviour of potential predators in northern and central Europe (75 species of mammals, raptors, owls, other birds and snakes) it was examined whether predation risk in microtine rodents varies in the course of the day. Relative predation risk was estimated for four different periods of the 24-h day (dawn, day, dusk and night) by means of an index I-pr. This index was calculated on the base of the activity pattern, the degree of prey specialization and the relative abundance of all resident predators in a given area. Day-time appeared as slightly more dangerous than twilight or night when only the activity patterns of potential predators were taken into account. A differentiated analysis including the predators' specialization on microtine prey, however, indicated that higher risk during day-time was mainly due to predators which take microtines only by chance. Risk due to predators which specifically search for microtines was almost evenly distributed over the 24-h day. Comparing estimated predation risk patterns in six example areas demonstrated that diel variations in predation risk are generally small, The evolutionary consequences of these findings are discussed with respect to the hypothesis that the peculiar activity pattern of microtines has evolved as a strategy of predator avoidance. It is concluded that predation risk is not minimized by the prey, and that predators probably adjust their hunting effort in accordance to the temporal pattern of prey availability.