1988 1990 1992 1994 1996 1998 2000 2002 Year
Figure 21.6. Cub survival (to seven days) per year. The declining annual trend was reversed in 1998.
age only; p — 0.32). In contrast, a detailed analysis of early survival rates over time found substantial improvements in cub survival to seven days of age (Fig. 21.6). From 1990 through 1997, cub survival decreased sharply, averaging less than 50% by 1997. Since 1998, however, survival has ranged from 73 to 90%, an improvement attributable to several factors. For instance, in 1998 and 1999 there was a new focus on the rearing of newborn cubs. When twins were produced, one cub was placed with the mother and the other in the nursery. The cubs were then switched frequently so that both could benefit from mother-rearing (see Chapter 13). This differed from previous protocols in which one cub remained with the mother while the other was relegated strictly to nursery-rearing. A new milk formula was also developed at this time and used to supplement twins or orphans (see Chapter 13).
Because there were no significant differences in survival rates over time for adults, overall pre- and post-1995 rates from captive-born and wild-caught animals were combined to allow comparing survivorship curves for male versus female giant pandas (Fig. 21.7). Although there was no gender difference (p > 0.05), the female survival curves tended to be higher than males because of a lower mortality for females that were one to two years of age.
Life table projections
To determine population viability and to help develop objectives for optimal population size, it is necessary to predict likely population
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