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Monthly samples totalling 202 European hares Lepus europaeus Pallas, 1778 were collected in southern Argentina from August 1993 to March 1994. The sex ratio of the whole sample was 1:1.2 in favour of females. Pregnant females were present from August to February and lactating females were present from September to March. The percentage of pregnant females was 59% for the whole breeding season. The mean ovulation rate for female hares was 2.78; the number of ova ovulated was not sig­nificantly correlated with body weight. The mean number of implantation sites per reproducing female was 2.46. The number of embryos in a litter varied from 1 to 4, the average being 2.12. The prenatal mortality was 56.5% of all ova ovulated and of these 34.7% were lost before implantation and 21.8% after implantation.
Exotic prey species can dramatically alter trophic interactions by functionally replacing native prey species. This pattern has been observed in the southern Neotropics, where introduced haresLepus europaeus Pallas, 1778 and rabbitsOryctolagus cuniculus (Linnaeus, 1758) have become the staple prey for native predators. Despite their importance as prey, no data are available on the mass and relative age of the lagomorphs on which native predators feed. We used linear regression models to predict the mass of lagomorphs from their hind-foot length, and investigated the influence of sex, season, and collection site on this relationship. Hind-foot length was a good predictor of body mass for both species and accounted for 58.4 and 71.6% of the variability in body mass for hares and rabbits, respectively. Sex and season significantly influenced the relationship, whereas the effect of collection site was negligible. Hind-foot length was also a good predictor of age class for hares and rabbits, allowing the discrimination between nonreproductive and reproductive classes for both species. Future research can use this method to determine the biomass and age class of exotic lagomorphs consumed by predators.
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