Three long-term demographic studies at Berenty and Beza Mahafaly have revealed much information concerning life history variables and population change over time (Gould et al., 2003; Jolly et al., 2002; Koyama et al., 2001, 2002). Average sex ratio at both sites is similar: 0.92 and 1:1 at Beza Mahafaly and Berenty, respectively (Gould et al., 2003; Koyama et al., 2002). Jolly et al. (2002) note much variation in sex ratio per ring-tailed lemur troop. Similar variation is also seen at Beza Mahafaly, and there seems to be no correlation with habitat, that is, sex ratios fluctuate constantly in both gallery and xerophytic forest (Gould et al., 2003; Sussman, 1991).
Mean fecundity at Berenty over a 19-year period was 75%, whereas at Beza Mahafaly it was 84% over 15 years (Gould et al., 2003; Jolly et al., 2002). Koyama et al. (2001), working in a very densely populated, 14-ha area of Berenty, found that while fecundity among very young (2-year-old) females was low (11%), it increased as a function of age and reached 75-85% for females between 5 and 10 years of age. At Beza Mahafaly, variation in fecundity occurred during and following a 2-year drought, with the lowest percentage at the end of the second drought year (74%) and the highest 2 years later (100%).
Jolly et al. (2002) report fewer infants per female in larger groups at Berenty, and Takahata et al. (2005) found that lower-ranking females in such groups exhibited lower reproductive success.
Infant mortality varies between the two sites and between habitats. In the rich and water provisioned area where Koyama and collegues' (2001) focal groups resided, infant mortality in the first year of life was just 37% in a year of normal rainfall whereas Jolly et al. (2003) report 50% in the scrub forest area of the reserve. At Beza Mahafaly, 80% of infants died in the first 6 months in the second year of a drought. But even in years of normal rainfall, infant mortality averages around 52% (Gould et al., 2003; Sussman, 1991). Such high infant mortality may be related to the suggestion by Gould et al. (2003) that L. catta are "income breeders" rather than "capital breeders" (as per Jonsson, 1997), that is, females do not rely upon fat stores during reproduction, rather they use the maximum resources in the environment when pregnant and lactating. Therefore, during natural disasters such as drought periods, when fruiting failures occur, females may simply not have the physiological capacity to adequately nurse their quickly growing infants.
In the wild, adult male L. catta become sexually mature around 3 years of age, and some disperse at that time, while others remain in the group until they are four (Gould, 2006; Koyama et al., 2002; Sussman, 1992). Koyama et al. observed some 2-year-old males disperse at his study area at Berenty. Two-year-old dispersal, like 2-year-old female births in that area of Berenty, may be a reflection of the rich resources, and water provisioning which does not occur in other areas of the reserve, i.e., sexual maturity in some animals may occur at an accelerated pace under certain favorable conditions. Also variable is the number of times a male might disperse in his lifetime: Koyama reported that male tenure varied between 1 and 7 years during his 10-year study, and at Beza Mahafaly, some males tend to disperse almost annually, while others can remain in one group for several years (Gould, unpublished data; Sussman, 1992). Sussman (1992) notes that on average, males migrate to another group every 3.5 years. Males usually disperse with one or two migration partners (Gould, 1994, 1997; Jones, 1983; Sussman, 1991, 1992).
Few data exist on maximum life span in wild L. catta. Koyama et al. (2002) noted that some females in their study groups lived past 13 years, but only one male reached that age. At Beza Mahafaly, animals were individually identified by means of a collar and numbered tag, and one female of known age survived until the age of 19 (Gould, unpublished data). A few other females, whose ages were known when they were initially collared, lived until 16 and 17 years (Gould et al., 2003). The oldest male of known age was 16 in 2005 (Gould, unpublished data, Sauther, personal communication). However, most animals die before reaching these ages (Gould et al., 2003; Koyama et al., 2002). It would be useful to have data on life expectancy and life span of ring-tailed lemurs living in habitats other than gallery and deciduous forest; however, long-term population studies are difficult to conduct in areas where animals are not easily habituated or protected.
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