~ This page was made as part of an undergraduate course at Davidson College ~
Social Spacing
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Two dwarf mongooses from the same den [Photo courtesy of Kees Bakker. Permission Pending].
What kind of groups do dwarf mongooses live in?
Dwarf mongooses live in packs of varying sizes, from 2 to 18 members; the average pack size is 8.4. Packs usually consist of 2 to 3 adult males, 3 to 4 adult females, and 2 to 3 juveniles (Skelton).
What determines the size of these groups?
Group size is determined by vigilance behavior (please see the section on Social Cooperation). Because predation is the biggest threat to the dwarf mongoose's life, it is essential for the packs to have protection from predation; one type of protection comes from subordinate dwarf mongooses that stand guard while the pack goes hunting. Subordinate males do almost all the guarding; they invest about 20% of potential foraging time in vigilance. Group size is dependent on these guards; the number of young that survive is positively correlated with groups size (a larger groups has more vigilance and more power in group attacks). However, at an individual level, maximal fitness is attained in smaller group sizes than the mean because dominant and subordinate animals have different optimal group sizes. Larger group sizes reduces costs to the guards, and so costs are decreased for subordinate males in group sizes larger than average (9-15 members). Therefore, there is a fine balance between the dominant pair wanting to keep groups small and subordinates wanting to keep groups large, resulting in the final reported average of 8.4 members per pack (Rasa, "The costs...").
What kind of areas do they occupy?
Classification of the dwarf mongoose's social spacing is not easy. These creatures live on home ranges varying in size from about 30 ha to 160 ha in the tree savannah areas. Despite the fact that they live on undefended home ranges, dwarf mongooses will defend small territories--their dens--on those home ranges. There are about 10-20 dens per home range (about 1.73 dens per acre). Home ranges of different packs do overlap sometimes; therefore, dwarf mongooses must mark their home ranges. Boundaries of the range are marked by anal gland and cheek gland secretions. In the case that a den (especially a valuable one, like a termite mound) is in the overlap region, neighboring packs may fight over posession of it, with the larger, more established pack usually gaining access to the den (Skelton). Despite their possessiveness over these territories, dwarf mongooses will migrate among territories on their home range everly 2 to 3 months. A possible explanation for this behavior has to do with food sources: this form of migration is associated with food depletion in the territorial areas (Rasa, 1977).
Why do they have the social spacing that they have?
As previously stated, predation is the biggest factor in determining not only their group size but also their social space. Dwarf mongooses must be socially organized in a group to protect themselves from predation. Similarly, they must live on home ranges because they cannot expend extra energy defending a large territory; they are too busy defending themselves. Part of protecting themselves, however, involves maintaining good hiding spots. They maintain these hiding spots by defending certain termite mounds and other covered areas. Because these termite mounds (or dens, as they are called) are defended and they are places in which dwarf mongooses mate, nest, and eat, they are described as classical territories.
Do dwarf mongoose packs use a rank system among themselves?
Yes!
Well, how does it work?
Dwarf mongooses live in matriarchal family groups. Each group has a dominant female, a dominant male, subordinate males and females, and yearlings. The dominant male ranks slightly below the dominant female, who is the founder of the group. Next in rank are the youngest individuals, who rank higher than their older siblings. The oldest animals (besides the dominant pair) rank the lowest in the pack. Within the age groups, females rank higher than males (Rasa, 1977). There are many speculations regarding why younger dwarf mongooses enjoy a higher rank than older dwarf mongooses. The most likely of these speculations is that the younger an individual is, the more assistance it will need in protection and in attaining food. Therefore, in order to ensure that it does get food, it has a higher rank, and therefore priority on the food when the pack comes back to the den from foraging.
Are dwarf mongooses stuck in the same pack forever?
Nope. However, dispersal is dangerous because of the fatal threat of predation. In mammals, male emigration is believed to be an inbreeding avoidance mechanism to reduce negative fitness consequences. However, this data suggests that the dwarf mongoose is an exception to this rule because breeding pairs in packs were generally closely related and there was no negative effect on offspring production, offspring survival or adult survival (Waser et al.). Among dwarf mongoose packs, inbreeding occurs for 3 reasons: