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This paper describes the density fluctuations of the adder Vipera berus and its prey during seven years. The reproduction during high adder density and low food availability was compared with that seven years later in the same population during low adder density and high food availability. Female length was similar but weight status (mass/length 2.56) was significantly higher during high prey density. Female mass loss when giving birth and clutch mass were significantly higher during high availability of food, but relative clutch mass and relative mass loss were similar in the two situations. However, the variance in relative clutch mass was significantly lower with high prey density. Clutch size and mass per young were significantly higher during high prey density. During high food availability there were significant positive correlations between female length (~ age) and birth mass loss, female length and clutch mass, female length and clutch size, clutch mass and mass per young and between relative clutch mass and mass per young. During low food availability there were significant positive correlations between clutch mass and clutch size and relative clutch mass and clutch size. A significant negative correlation was found between female length and relative mass loss. This study do not conform entirely to general theories on reproductive adaptations to varying food availability (r-K strategies). During high prey density both more and heavier young were produced than during scarcity of food. A high correlation of reproductive parameters during high food availability indicates a maximal utilization of reproductive capacity in most females, while the lack of such correlations during low food availability indicates a varying access to food and fat storage possibility among females.

Reproductive Tactics in an Island Population of Adders, Vipera berus (L.), with a fluctuating Food Resource