Age-specific survival in five populations of ungulates: Evidence of senescence

Methodological problems in describing patterns of senescence in wild popula tions have until recently impeded progress in understanding the evolution o f a process that decreases individual fitness, We investigated age- and sex -specific survival in five populations of three species of ungulates (roe d eer, Capreolus capreolus; bighorn sheep, Ovis canadensis; and isard, Rupica pra pyrenaica), using recent statistical developments of capture-mark-recap ture models and long-term (12 to 22 yr) data on marked individuals. The yea rly survival of females aged 2-7 yr was remarkably similar and very high (9 2-95%) in all five populations. Survival of adult males varied among specie s and populations. Survival decreased from 8 yr onward for both sexes in al l populations, suggesting that senescence was a common phenomenon. Male sur vival was lower than female survival, and the gender difference increased w ith age. The extent of sex differences in survival was related neither to s exual dimorphism in mass nor to the level of polygyny, suggesting that spec ies differences in social behavior, particularly mating system and the leve l of male-male aggression, may be more important than simply the level of p olygyny in explaining sexual differences in survival. Our results underline the advantages of long-term monitoring of marked individuals for the study of evolutionary ecology.