Comparative analyses of life-history strategies in Asiatic and African wild asses using a demographical approach

Abstract. Trade-offs such as the ones between reproduction and longevity or present and future reproduction are believed to shape reproductive patterns. We here used zoo data to investigate trade-offs and life histories in four taxa of Asiatic (Equus hemionus ssp.) and African wild asses (Equus africanus ssp.). All taxa showed even in captivity peak birth rates during the periods of highest food availability in their natural environments. Sex-specific survival rates with females living longer than males were evident in kulan and onager but not in kiang and Somali wild ass, pointing towards different life-history strategies even among closely related taxa. Females achieved their highest reproductive output earlier in life than males, which is typical for polygynous mating systems. Offspring number and longevity were positively rather than negatively correlated. Taken together evidence for reproductive trade-offs was weak, though the length of the reproductive period was negatively related to birth rates within the reproductive period. Birth intervals increased with female age, probably reflecting detrimental effects of senescence. Despite several limitations, zoo data seem to be useful to better understand the reproductive biology of endangered, rare or cryptic species.