DELAYED AND INVERSE DENSITY-DEPENDENCE IN A CHAMOIS POPULATION OF THEITALIAN ALPS

Both density dependent and density independent factors have been consi dered important determinants of the dynamics of ungulate populations. Intraspecific competition for food and the amount of snow cover were s uggested in the past as factors that influence the demographic paramet ers of the chamois Rupicapra rupicapra. We present a 10 yr study on a closed population of the Italian Alps. Animals, divided by sex and age class (kid, yearling, subadult, adult, old), were counted over the pe riod 1981-1990. The number of chamois hunted and the number of carcass es found each year and the daily snow height were also available. We i nvestigated possible correlations between several demographic paramete rs and both snow cover and chamois density, accounting for sex- and ag e-differential mortality and a possible delay in density dependence. R esults are as follows: a) there is no statistically significant correl ation between snow cover and demographic rates; b) there is no detecta ble compensation between natural and hunting-related mortality; c) bir th rate is density independent for any time delay; d) when calculated from carcasses, total mortality, mortality of 1-yr-old and older males and females significantly depend on total density with 2 years' lag, while kid mortality is not related to density for any time delay; e) w hen calculated from censuses, all mortality rates significantly depend on total density with 2 years' lag, although the variance explained b y delayed density is definitely smaller for kids; f) nonlinear regress ion of kid mortality from censuses against density of kids in the same year yields a much higher coefficient of determination and inverse de nsity dependence is evidenced. However, discrimination between delayed and inverse density dependence in kid mortality is impossible, given our dataset. In general, results support the hypothesis that intraspec ific competition, epidemics and predation, rather than weather, play a role in the dynamics of this ungulate population.