BREEDING PHENOLOGICAL STRATEGIES OF THE COMMON WOODLOUSE, PORCELLIO SCABER (ISOPODA, ONISCIDEA)

In a phenological investigation on terrestrial isopods in the area sur rounding Cologne, Germany, populations of Porcellio scaber showed two distinct breeding waves. While larger gravid females were found during the entire reproductive period, gravidity in smaller females was rest ricted to the second breeding wave. Juveniles derived from different b reeding waves showed remarkable differences concerning their size at t he end of our investigations. Furthermore, a striking variability in t he size of juveniles of the same age was observed. These differences i n size result in two distinct phenological strategies of females withi n the same population: Larger 1-year-old females are able to reproduce in the second breeding wave during summer, while smaller 1-year-old f emales do not reproduce, but are able to grow. These females will repr oduce in the following spring at the age of 1 1/2-2 years. Consequence s of these phenological strategies are discussed with respect to the r eproductive success of single females.