Evol Ecol Res 5: 229-237 (2003)     Full PDF if your library subscribes.

Natural selection on individual clutch size–

laying date trends in the Ural owl

Jon E. Brommer,1* Hannu Pietiäinen1 and Heikki Kolunen2

1Bird Ecology Unit, Department of Ecology and Systematics, University of Helsinki, PO Box 65 (Viikinkaari 1), FIN-00014 Helsinki and 2Niikarinkatu 52, FIN-15500 Lahti, Finland

Author to whom all correspondence should be addressed.
e-mail: jon.brommer@helsinki.fi


Clutch size declines with advancing laying date in many birds. This relationship is thought to represent a reaction norm of individual optimization in response to local environmental conditions. This implies that: (1) individuals should vary in the properties of their clutch size–laying date trends; (2) these differences should be reflected in their fitness; and (3) parts of this variation should be heritable. Here, we show that 44 Ural owl females of known lifespan, with a statistically sufficient number (≥ 5) of clutch size–laying date observations each, differed individually both in the slope and the elevation of their clutch size–laying date relationships. As an estimate of individual fitness, we used the lifetime production of fledglings, which is a known correlate of recruitment in this population. Females with a higher elevation had a higher lifetime reproductive success. However, plasticity – that is, the slope of the clutch size–laying date relationship – did not have apparent advantages in terms of a female’s fitness.

Keywords: clutch size–laying date trend, life history, lifetime reproductive success, phenotypic plasticity, Strix uralensis, Ural owl.

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