References: (1) Bowman and Lee (1995). (2) Johnson and Kapsalis (1995). (3) Mori (1979). (4) Melnick and Pearl (1987). (5) Janson and van Schaik (1993). (6) Altmann and Alberts (1987); Altmann et al. (1993). (7) Glassman et al. (1984). (8) Bercovitch (1987); Strum (1991); Smuts and Nicolson (1989). (9) Coelho (1985). (10) Leigh and Shea (1996). (11) Fedigan and Rose (1995). (12) Howell (1979); Truswell and Hansen (1976). (13) Prentice et al. (1986). (14) Short et al. (1991).
m = males only; c = estimated from regression; e = growth rate necessary to wean at weight predicted by MW for reported duration of lactation. Data are presented on maternal mass (MM), wean weights (WW), interbirth intervals (Lact mo) and growth rates (GR g/d); species averages are given in bold. Italicised data are calculated from allometric equations when no data were available. Lactation duration for captive species is given in italics as the average minimum for the species range when not specified for populations. Weaning weights predicted by the regression equations for growth rate (GR2), birth mass (BM2) and maternal mass (MM2) are presented for comparison. All units of mass are in kilograms.
what more costly in terms of their growth rates). Suckling patterns, which influence reconception through the mechanism of lactational anovulation, appear to underlie the differences in growth rates to the weaning threshold and thus the duration of lactation. High rates of suckling in both rhesus and vervet monkeys are associated with rapid growth, but a lower likelihood of conception, while low rates of suckling are associated with slower growth and reconception (Lee and Bowman, 1995). Mothers appear to balance the costs of ensuring growth for a current infant against their ability to reconceive - trading-off rapid but prolonged offspring growth with no reconception, against slower offspring growth to a minimal weaning threshold with reconception. The trade-off here concerns both maternal reproduction and infant survival, mediated by growth rates to the threshold. A study of rhesus infants (Johnson and Kapsalis, 1995) found that growth was a function of maternal body mass index (a condition index), as well as of infant sex. This is strong evidence for an effect of maternal condition on infant growth, also apparent in food-limited baboon populations (Strum, 1991; Altmann et al., 1993) and in captive vervets (Fairbanks and McGuire, 1996).
Trends in growth to a threshold mass within species are similar to those predicted from interspecific comparisons (Table 5.5). What is most striking is that local ecology affects maternal size and either growth rates or their correlate - duration of lactation - most dramatically, while weight at weaning is predicted to vary relatively little. However, while suggesting a general mammalian trend in the attainment of weaning weight from which the primates as a group deviate relatively little, the intraspecific data do not yet confirm the hypothesis. Further tests are needed, based on studies of variation between individuals within species. By determining sources of variance in growth to weaning between individuals, we can better identify the constraints and selective pressures acting on patterns of growth as a life history variable.
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