As no Alpine ibex population is nowadays regulated significantly by the presence of natural predators, the factors that act on the dynamics of these populations are essentially linked to density, meteorological events, and, to a lesser extent, diseases, avalanches, hunting and poaching (Wiersema, 1989).

Local epidemics of some diseases, such as Mycoplasma conjunctivae and respiratory infections, have certainly caused alarm and attracted the attention of public opinion, but such events caused little effect on the dynamics of populations (Hars & Gauthier, 1984). An exception is represented by sarcoptic mange which, in case of epidemics, can cause devastating effects on wild ungulate populations, with significant mortality rates (in same cases higher than 90 %).

Density-dependent effects, have been widely described, and act through the lengthening of population renewal times, the increase of the age of primiparity in females and reduction of birth rate (Nievergelt, 1966). The yearly increment rate of alpine ibex populations thus varies primarily as a function of population maturity and density. Values oscillating between 10 % and 18.3 % have been reported in the literature (Linzi, 1978; Kofler, 1981; Ratti, 1981). The reduction of the birth rate in high density populations depends mostly from the reduction of the available feeding resources rather than from factors affecting fecundity, as shown in the Albris population in Switzerland. In this population, although the population increase rate and the mean number of kids per female is low, the mean fecundity rate oscillates around 88% with maximum values of 100%, recorded in females 4 years old (Giacometti e Ratti, 1994).
Even if the effects of snow precipitation and rigid winters have been described in the past (Niervergelt, 1966; Linzi, 1978), the importance of climatic factors on the dynamics of a ibex population has been shown only recently (von Hardenberg et al., 2000). The ibex population of Gran Paradiso National Park, regularly counted since 1956, shows variations in density tightly linked to yearly changes in snow precipitation. In this population, periodic fluctuations in population size, with an interval of 3 and 8 years, respectively due to changes in the numbers of kids and adults, have been reported (Bassano et al., 1992; von Hardenberg et al., 2000). The reasons of these oscillations is still to be cleared.

Winter mortality is an event of great importance especially in high density protected areas and it is due not only to a reduction of nutrients during the winter but also to an insufficient accumulation of reserves during the summer (Bassano e Mussa, 1998).

Survival probability of males and females is high and does not differ significantly among the two sexes. This result is surprising as the two genders are highly dimorphic. In both genders the survival rate is near to 97% (Toïgo et al., 1997). These high survival rates are probably the cause of the variations recorded in the Gran Paradiso population structure: after winters with low snow precipitation, an inversion of the sex-ratio in favour of males and a progressive ageing of the population, has been recorded. The percentage of males aged more than 6 years increased from 46 to 56.5% in only 8 years and 33% of these males is older than 10 years. Winter mortality hits mostly the most represented age classes and particularly males aged between 10 and 14 years (Bassano & Peracino, 1994).hybrids born in Haute Savoie in 1985, Gauthier et al., 1991).