Costs of reproduction—A demographical approach to examine life-history trade-offs in two old-world deer species

Resource-allocation trade-offs comprise fundamental constraints on life-history evolution. In particular, the trade-offs between reproduction and longevity and between present and future reproduction are believed to be important in shaping reproductive patterns. Unfortunately, exploring such trade-offs in natural populations is complicated and may not be possible in all taxa. Against this background we here use zoo data for enhancing our understanding of reproductive patterns in two endangered and cryptic deer species (Vietnamese sika deer Cervus nippon pseudaxis, Mesopotamian fallow deer Dama dama mesopotamica). In both species, births peaked right before the onset of the rainy season in the species’ natural environments. Females reached high reproductive output earlier in life and had (in one species only) higher survival rates than males. Offspring number covaried positively rather than negatively with longevity. In females, the length of the reproductive phase correlated positively with longevity, birth rate within the entire lifespan, and offspring number, while it was negatively related to the birth rate during the reproductive phase (in 1 species). The length of the post-reproductive phase was positively related to longevity and negatively to the birth rate during the entire lifespan. Taken together, we revealed several patterns being presumably of ecological relevance including indications for trade-offs among offspring quality and quantity, and between present and future reproduction even within these captive populations relieved from seasonal (e.g. food) constraints. In spite of some limitations, our study reconfirms that zoo data offer insights into the reproductive biology of species for which field data are difficult to obtain.