Summary 0[ In social mammals where group members cooperate to detect predators and raise young\ members of small groups commonly show higher mortality or lower breeding success than members of large ones[ It is generally assumed that this is because large group size allows individuals to detect or repel predators more e}ectively but other bene_ts of group size may also be involved\ including reduced costs of raising young and more e}ective competition for resources with neighbouring groups[ 1[ To investigate the extent to which predation rate a}ects survival\ we compared mortality rates in two populations of suricates "Suricata suricatta#\ one living in an area of high predator density "Kalahari Gemsbok Park# and one living in an area of relatively low predator density "neighbouring ranchland#[ Most aspects of feeding ecology and growth "including time spent feeding\ daily weight gain\ growth\ adult body weight\ breeding frequency and neonatal mortality# were similar in the two populations[ In contrast\ mortality of animals over 2 months old was 0=6 times higher in the Park than on ranchland[ 2[ Mortality of juveniles between emergence from the natal burrow and 5 months of age was higher in small groups than large ones in the Park but signi_cantly lower in small groups than large ones on ranchland[ Adult mortality declined in larger groups in both areas[ 3[ The tendency for survival to be low in small groups had far!reaching consequences for the risk of group extinction[ During a year of low rainfall in the Park\ all groups of less than nine animals became extinct and population density declined to around a third of its initial level[ We argue that high group extinction rates are to be expected in species where survival declines in small groups and mortality rates are high[ Key!words] cooperative breeding\ demography\ mammals\ mortality[ Journal of Animal Ecology "0888# 57\ 561Ð572

Functional interpretations of helping behaviour suggest that it has evolved because helpers increase their direct or indirect fitness by helping. However, recent critiques have suggested that helping may be an unselected extension of normal parental behaviour, pointing to evidence that all mature individuals commonly respond to begging young (whether they are parents, relatives or non-relatives) as well as to the lack of evidence that cooperative activities have appreciable costs to helpers. Here we provide an example of one form of cooperative behaviour that is seldom performed by parents and has substantial energetic costs to helpers. In the cooperative mongoose, Suricata suricatta, non-breeding adults commonly babysit young pups at the natal burrow for a day at a time, foregoing feeding for 24 hours. Parents rarely contribute to babysitting, and babysitting has substantial energetic costs to helpers. Members of small groups compensate for the reduced number of participants by babysitting more frequently, and neither the proportion of time that babysitters are present nor the survival of litters vary with group size.

SummaryIn most respects, the demography of Kalahari suricates (Suricata suricatta) resembles that of other social mongooses. Average group size varies from four to nine, and groups typically include several mature females, of which one is responsible for the majority of breeding attempts. Breeding females show a postpartum oestrus; gestation is around 60 days; litter size is three to five pups at emergence and females rarely breed before the age of 24 months. In contrast, annual survival rates (0.20 for pups and 0.43 for animals over one year old) are lower than those recorded in other species. Breeding frequency is related to rainfall and breeding can cease altogether when rainfall is unusually low. In a year when this occurred, group size eroded rapidly and over 60% of groups became extinct. Total numbers were slow to recover during the following year because emigration by females was infrequent and new groups did not form in vacant ranges created by the extinction of groups. High rates of group extinction have been found in other cooperative breeders and may occur because breeding success and survival show inverse density dependence. Key words: cooperative breeding, population dynamics, suricates RésuméPar bien des aspects, la démographie des suricates du Kalahari (Suricata suricatta) ressemble à celle des autres mangoustes sociales. La taille moyenne des groupes varie de quatre à neuf, et les groupes comprennent typiquement plusieurs femelles mâtures dont une est responsable de la majorité des tentatives de reproduction. Les femelles reproductrices présentent un oestrus de post-partum; la gestation dure environ 60 jours; la portée compte de trois á cinq jeunes á la naissance, et les femelles se reproduisent rarement avent l'âge de 24 mois. Par contre, les taux de survie annuels (0,20 pour les petits et 0,43 pour les animaux de plus d'un an) sont plus faibles que ceux des autres espèces. La fréquence des reproductions est liée aux chutes de pluie, et elles peuvent même s'arrêter quand les pluies sont extraordinairement rares. Une année où ceci est arrivé, la taille des groupes s'est réduite rapidement et plus de 60% des groupes ont disparu. Le nombre total a mis du temps à remonter l'année suivante

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De Hoop Nature Reserve and a neighbouring conservancy contain the most genetically diverse subpopulation of the Endangered (IUCN) Cape mountain zebra (Equus zebra zebra Linnaeus 1758). Although vital for the long‐term stability of the meta‐population, the population had received limited monitoring post‐1999. We summarize data obtained during a population monitoring programme established in 2005. Ninety‐nine individuals were identified indicating a decline in annual population growth from 6.6% (1995–1999) to 4.5% (1999–2005). The population was male biased and the deficit of females is likely to have prevented additional breeding herd formation resulting in excess nonbreeding males. These animals are currently of limited reproductive value to the meta‐population and may be contributing to the decline in reproductive potential at De Hoop by competing for limited resources. One solution may be to translocate ‘excess’ males to reinforce existing small populations or establish new populations with females from elsewhere provided that a minimum of 78 animals is maintained at De Hoop to limit genetic loss. Population monitoring and effective management strategies for the De Hoop population and the meta‐population are vital to ensure the long‐term survival of Cape mountain zebra and for the success of other species recovery programmes.