Over-winter survival in subadult European rabbits: weather effects, density dependence, and the impact of individual characteristics.

The survival probability of an individual may be limited by density-dependent mechanisms and by environmental stochasticity, but can also be modified by individual characteristics. In our study, we investigated over-winter survival of subadults of an enclosed European rabbit Oryctolagus cuniculus population in a temperate zone habitat over the period 1992-2002. We: (1) selected for appropriate models to explain individual variation in over-winter survival and the animals' autumn body mass, the latter was used as a measure of the individual pre-winter body condition; and (2) aimed to compare the sensitivity of the target variables on the realised variation of the factors considered. Model selection based on information theory revealed that individual over-winter survival was best explained by the combination of autumn body mass, winter temperature, population density and sex, where the probability of survival was higher in females than in males. According to this model, the probability of survival reacted most sensitively to variation in the autumn body mass and in winter temperature. Individual autumn body mass was best explained by the combination of the date of birth, population density, and weather conditions by means of the percentage of rainy days during the first 2 months after the animals had emerged above ground, where the autumn body mass was negatively related to the percentage of rainy days. The chosen model suggested that the autumn body mass reacted most sensitively to variation in the date of birth. Combining these models, we found that weather conditions during two different periods of time as well as population density, sex and the date of birth operated together to determine the probability of over-winter survival. In particular, the study points out the high impact of environmental stochasticity on over-winter survival: (1) by direct effects of winter temperature conditions, and (2) by the indirect action of weather conditions to which the animals were exposed during the early period of juvenile development.