Reluctant challengers: why do subordinate female meerkats rarely displace their dominant mothers?

In most cooperatively breeding vertebrates, dominant breeders have higher reproductive success and live longer than subordinate helpers, and subordinates might consequently be expected to challenge the dominants in their group for status. However, in contrast to noncooperative species, challenges for dominance are rare. This could be because subordinates are unable to displace dominants or because the risk of attempting to do so is prohibitively high. Alternatively, because subordinates are commonly the offspring of dominants and more established breeders tend to produce more young, subordinates may maximize their inclusive fitness by allowing related dominants to maintain their position and helping them to raise future offspring. Here, we use more than 13 years of data from a wild population of Kalahari meerkats Suricata suricatta to investigate whether subordinate females would be likely to gain higher inclusive fitness by displacing their dominant mothers than by remaining as helpers. We first show that the breeding success of dominant females increases during the first 2-3 years of their tenure and then declines. Combining estimates of breeding success in each year of tenure with age-specific survival probabilities, we then calculate the reproductive value of successful challengers and nonchallengers. Our results show that, in any year, subordinate females would achieve higher inclusive fitness by displacing their dominant mother than by remaining as helpers. We conclude that the low frequency with which displacement occurs probably reflects the potential costs associated with challenging for status and the low probability of success.