Different Forms of Social Organization At High and Low Population Densities in Guinea Pigs

Abstract

[This 34 months' study was concerned with the social organization in a freely growing group of domestic guinea pigs from 8 to 24 individuals. At low numbers (4♂♂, 4♀♀-6♂♂, 8♀♀) the linear rank-order among the males was the most obvious characteristic of social structure. The alpha male's dominance was not locality dependent. He defended all females against all males. Attaining the alpha position was the most successful male reproductive strategy within this dominance structured system. At high numbers (7♂♂, 9♀♀-12♂♂, 12♀♀) a different, more complex social organization developed. Long-lasting social relationships between individual males and females as well as spatial relationships became predominant. The individuals filled different social positions which remained stable for months. The males could be divided into three different categories: 1. 'Owners', who lived together with 1 to 7 females, mainly in non-overlapping territorial areas, and who probably reproduced with these females. Their main strategy of enlarging their number of females was to recruit juvenile previously 'unowned' females into their harems. 2. Non-owners, who were dominated by the owners, formed preferences for the owners' females and, by displaying this strategy, usually attained ownership later. 3. The lowest ranking 'omega' males who were withdrawn from most social interactions. Their status can be viewed as a bad state with alternative options missing. The change of social organization took place within one month. It is seen as a mechanism to facilitate adjustment to increasing population density. The change may be instigated when it is no longer economical for the alpha male to monopolize all females and he therefore adopts an alternative reproductive strategy to maximize his fitness. The proximate factor releasing the change, may be the increasing number of fights between the alpha and beta males observed during this period., This 34 months' study was concerned with the social organization in a freely growing group of domestic guinea pigs from 8 to 24 individuals. At low numbers (4♂♂, 4♀♀-6♂♂, 8♀♀) the linear rank-order among the males was the most obvious characteristic of social structure. The alpha male's dominance was not locality dependent. He defended all females against all males. Attaining the alpha position was the most successful male reproductive strategy within this dominance structured system. At high numbers (7♂♂, 9♀♀-12♂♂, 12♀♀) a different, more complex social organization developed. Long-lasting social relationships between individual males and females as well as spatial relationships became predominant. The individuals filled different social positions which remained stable for months. The males could be divided into three different categories: 1. 'Owners', who lived together with 1 to 7 females, mainly in non-overlapping territorial areas, and who probably reproduced with these females. Their main strategy of enlarging their number of females was to recruit juvenile previously 'unowned' females into their harems. 2. Non-owners, who were dominated by the owners, formed preferences for the owners' females and, by displaying this strategy, usually attained ownership later. 3. The lowest ranking 'omega' males who were withdrawn from most social interactions. Their status can be viewed as a bad state with alternative options missing. The change of social organization took place within one month. It is seen as a mechanism to facilitate adjustment to increasing population density. The change may be instigated when it is no longer economical for the alpha male to monopolize all females and he therefore adopts an alternative reproductive strategy to maximize his fitness. The proximate factor releasing the change, may be the increasing number of fights between the alpha and beta males observed during this period.]