For large herbivores living seasonal environments at northern latitudes, the timing of breeding involves very different decisions for males and females. For females, timing is important to hit peak plant protein levels, but it also involves the decision on how to solve the trade-off between investment in current year offspring vs. future reproduction and survival. In reindeer, we manipulated females to reovulate to assess how they solved the latter decision. Late conceiving females produced fewer males, had 10 days shorter gestation times and the calves were 0.6 kg (9.2%) lighter at birth and 7.4 kg (14.7%) lighter in autumn. This suggests females are reducing the quality of this year’s offspring to ensure their own future reproduction and survival. In contrast, for males, the timing of reproductive effort is important to maximize number of females they can mate during autumn rut in competition with other males. The latter depend on when most females are ovulating, but also on how other males with a different competitive ability are timing use of their capital (fat); it may pay younger males to invest more heavily later when prime-aged males are exhausted. I present empirical data on timing of reproduction of both female and male red deer and how this is affected by factors such as age and population density. I present evidence suggesting that male rutting phenology is best interpreted as a compromise between hitting peak female ovulation and intensity of sexual selection.

Atle Mysterud
Professor
Centre for Ecological and Evolutionary Synthesis (CEES)
Department of Biology
University of Oslo
P.O. Box 1066 Blindern
N-0316 Oslo, Norway
tel. (+47) 22 85 40 45; fax. (+47) 22 85 47 26
E-mail:atle.mysterud@bio.uio.no
http://folk.uio.no/atlemy/