POPULATION-DYNAMICS AND REGULATION IN THE COYPU MYOCASTOR COYPUS IN CENTRAL ITALY

A capture-recapture design was applied between January 1989 and June 1 991 in a 37.5 ha area located in the central valley of the Tiber River (Latium), aimed at estimating the demographic parameters of a coypu p opulation in the Mediterranean climate and at preliminarily investigat ing the factors that regulate its numbers in this region. The populati on fluctuated between 27 and 137 individuals and followed a seasonal p attern: it decreased after the winter and increased between summer and winter. Density remained almost stable during a particularly mild win ter. Survival rates remained relatively high over the entire study per iod; reproductive activity and additions to the population from in sit u reproduction, however, showed minimum peaks following colder winters . Evidence of immigration was detected during periods of increasing de nsity. Key factor acid preliminary density dependence analyses showed that pregnancy failure and new-born losses are cumulatively the most i mportant factor contributing to variation in total mortality, and are positively related to coypu numbers in previous periods. The failure t o realize maximum potential fecundity is inversely related to previous coypu abundance. We show that post-recruitment losses play only a min or role in determining population decline.