Litter size and latitude in a large mammal: the wild boar Sus scrofa

A positive relationship between clutch size or litter size and latitude exists in birds and many species of small mammal. Hitherto, however, analyses for large mammals have failed to provide evidence that litter sizes increase with latitude. We collated data from published studies of wild boar in Europe, to analyse the relationship between litter size and latitude in this widely distributed terrestrial mammal. Depending on the specific data set (whether only the most reliable data or all available data were included), latitude explained 58% to 72% of the variation in mean litter sizes across studies. On average, litter size increases by approximately 0.15 piglets per degree of latitude. A strong correlation between litter size and latitude for wild boar in Europe provides a starting point for demographic modelling of this species of both ecological and economic importance. The pattern for wild boar is consistent with Ashmole's explanation for the effects of latitude on reproduction. The contrast between our results and those generated for other large mammals may result from our focus on an herbivore in contrast to previous work which was focused on carnivores. Further work could usefully examine the extent of seasonality in the availability of resources for species of different dietary types.