Even mortality patterns of the two sexes in a polygynous, near-monomorphic species: is there a flaw?

The chamois Rupicapra rupicapra has been termed a highly polygynous species, with a great male competition for mating. If so, a lower survival should be expected for the male sex. From 1986 to 2000, 1801 carcasses of chamois were collected in the Maritime Alps Regional Park, Italy, where a protected, healthy, stable population of chamois occurred (c. 12 individuals 100 ha-1). Each year, population structure from carcasses was consistent with that from the count carried out on the preceding year on live individuals. Demographic features (assessed from mortality data, as well as from live counts) showed a balanced age structure and a good adult survival (10% individuals older than 11 years). Mortality peaks showed a cyclic pattern of 3-4 years. Winter severity and local density affected survival, with no significant difference between sexes. The number of carcasses was dependent on the combination of snow depth and mean temperature, in winter. Both sexes showed nearly the same survivorship curves, with a quite similar life expectancy in the first year (males=6.8 years, females=7.0 years), and the same maximum age at death (16 years), as it may be expected in a monomorphic, monogamous species. This is, however, a rare event among polygynous species, with a high male competition for females and male juvenile dispersion, which normally affect male survival. The similar adult survival of the two sexes could be explained by comparable energetic costs and risks for reproduction, or through greater fat reserves put on by males, before the rut, which may lower their winter mortality. © 2010 The Authors. Journal compilation © 2010 The Zoological Society of London.