Sex‐ and age‐specific survival of the highly dimorphic Alpine ibex: evidence for a conservative life‐history tactic

Abstract

1. Age-specific survival of 215 males and 117 females of the highly sexually dimorphic Alpine ibex Capra ibex (L.) was assessed from a 21-year capture-mark-recapture (CMR) programme (1983-2004). The study covered two contrasted periods of population performance (high performance from 1983 to 1997 vs. low performance from 1998 onwards). 2. Based on current life-history theories for sexually dimorphic species, we expected that survival should decrease with age in both sexes, female survival should be buffered against environmental variations, male survival should decrease during the low performance period, and adult survival should be lower in males than females during the low performance period. 3. Survival of both sexes was strongly affected by age, with the four age classes (yearling, prime-aged adults of 2-8 years of age, old adults of 8-13 years of age, and senescent adults from 13 years of age onwards) generally reported for large herbivores. 4. Survival of females at all ages, and of yearling and prime-aged males, was buffered against environmental variations and was the same during periods of high and low population performance. The survival of old males decreased in years of low population performance. 5. All marked yearlings (32 females, 56 males) survived to age 2. Survival of prime-aged females (0.996 +/- 0.011) was higher than for other large herbivores, but similarly to other large herbivore species, it declined slowly and regularly with increasing age afterwards. Male survival was 5-15% higher each year than that of males of other large herbivores. Males enjoyed very high survival when prime-aged (0.981 +/- 0.009) and as old adults (high-performance period: 0.965 +/- 0.028, low-performance period: 0.847 +/- 0.032). 6. The very high survival of males, coupled with their prolonged mass gain, suggests a highly conservative reproductive tactic. Male ibex differ from similar-sized herbivores by showing a nearly indeterminate growth in horn size and body mass. By surviving to an advanced age, males may enjoy high reproductive success because of their large size.