vol. 173, no. 1 the american naturalist january 2009  Age, Size, and Spatiotemporal Variation in Ovulation Patterns of a Seasonal Breeder, the Norwegian Moose (Alces alces) Mathieu Garel, 1,2,3,* Erling Johan Solberg, 4,† Bernt-Erik Sæther, 2,‡ Vidar Grøtan, 2,§ Jarle Tufto, 5,k and Morten Heim 4,# 1. Universite ´ de Lyon, Centre National de la Recherche Scientifique, Unite ´ Mixte de Recherche 5558, Laboratoire de Biome ´trie et Biologie E ´ volutive, 43 Boulevard du 11 Novembre 1918, Villeurbanne F-69622, France; 2. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway; 3. Office National de la Chasse et de la Faune Sauvage, Centre National d’E ´ tude et de Recherche Applique ´e sur la Faune de Montagne, 95 rue Pierre Flourens, BP 74267, 34098 Montpellier Cedex 05, France; 4. Norwegian Institute for Nature Research, NO-7485 Trondheim, Norway; 5. Centre for Conservation Biology, Department of Mathematical Sciences, Norwegian University of Science and Technology, NO- 7491 Trondheim, Norway Submitted February 1, 2008; Accepted August 6, 2008; Electronically published December 10, 2008 Online enhancement: appendix. abstract: In seasonal environments, timing of reproduction is an important fitness component. However, in ungulates, our under- standing of this biological process is limited. Here we analyze how age and body mass affect spatiotemporal variation in timing of ovu- lation of 6,178 Norwegian moose. We introduced a parametric sta- tistical model to obtain inferences about the seasonal timing of ovu- lation peak, the degree of synchrony among individuals, and the proportion of individuals that ovulate. These components showed much more spatiotemporal variation than previously reported. Young (primiparous) and old (≥11.5 years of age) females ovulated later * Corresponding author; e-mail: mgarel@biomserv.univ-lyon1.fr. † E-mail: erling.solberg@nina.no. ‡ E-mail: bernt-erik.sather@bio.ntnu.no. § E-mail: vidar.grotan@bio.ntnu.no. k E-mail: jarlet@math.ntnu.no. # E-mail: morten.heim@nina.no. Am. Nat. 2009. Vol. 173, pp. 89–104.  2009 by The University of Chicago. 0003-0147/2009/17301-50234$15.00. All rights reserved. DOI: 10.1086/593359 than prime-aged (2.5–10.5 years of age) females. In all age classes, ovulation was delayed with decreasing body mass. Ovulation rates were lower and more variable among primiparous females than among older females. Young females required higher body mass than older females did to ovulate. The body-mass-to-ovulation relation- ship varied with age, showed large regional variation, and differed among years within region. These results suggest that (1) environ- mental and population characteristics contribute to shape seasonal variation in the breeding pattern and (2) large regional variation exists in the size-dependent age at maturity in moose. Hence, the life-history trade-off between reproduction and body growth should differ regionally in moose. Keywords: age, body mass, ecological modeling, life-history theory, reproduction, ungulates. Introduction In studies of ungulates, information about age-specific vi- tal rates, such as reproduction and survival, is strongly required to understand the population dynamics and to develop management strategies (Pojar 1981; Coulson et al. 2001). In this context, reproductive parameters are of- ten easier to measure than survival, and the mechanisms causing individual variation in fecundity are therefore fairly well known in many mammalian populations (Sæther 1997; Gaillard et al. 2000). Whereas detailed in- formation is available about factors structuring female re- productive output, our knowledge about the variations in ovulation patterns is still scarce. However, as variations in ovulation dates and subsequent variations in timing of birth are likely to influence the population dynamics through their effects on juvenile body mass (Albon et al. 1987; Sæther et al. 2003; Holand et al. 2006a), growth rates (Albon et al. 1987; Clutton-Brock et al. 1992; An- dersen and Linnell 1997; Lindstro ¨m 1999; Holand et al. 2006a), and summer (Festa-Bianchet 1988b) and winter survival (Clutton-Brock et al. 1987; Gaillard et al. 1996; Rose et al. 1998; Loison et al. 1999), variation in breeding phenology may also have strong evolutionary and man- agement implications. Seasonal variation in timing of breeding and synchrony