Unpredictable food supply modifies costs of reprod

Authors: János Török Gergely Hegyi László Tóth Réka Könczey

Publish Date: 2004/08/17

Volume: 141, Issue: 3, Pages: 432-443

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Abstract

Investment into the current reproductive attempt is thought to be at the expense of survival and/or future reproduction Individuals are therefore expected to adjust their decisions to their physiological state and predictable aspects of environmental quality The main predictions of the individual optimization hypothesis for bird clutch sizes are 1 an increase in the number of recruits with an increasing number of eggs in natural broods with no corresponding impairment of parental survival or future reproduction and 2 a decrease in the fitness of parents in response to both negative and positive brood size manipulation as a result of a low number of recruits poor future reproduction of parents or both We analysed environmental influences on costs and optimization of reproduction on 6 years of natural and experimentally manipulated broods in a Central European population of the collared flycatcher Based on dramatic differences in caterpillar availability we classified breeding seasons as average and rich food years The categorization was substantiated by the majority of present and future fitness components of adults and offspring Neither observational nor experimental data supported the individual optimization hypothesis in contrast to a Scandinavian population of the species The quality of fledglings deteriorated and the number of recruits did not increase with natural clutch size Manipulation revealed significant costs of reproduction to female parents in terms of future reproductive potential However the influence of manipulation on recruitment was linear with no significant polynomial effect The number of recruits increased with manipulation in rich food years and tended to decrease in average years so control broods did not recruit more young than manipulated broods in any of the year types This indicates that females did not optimize their clutch size and that they generally laid fewer eggs than optimal in rich food years Mean yearly clutch size did not follow food availability which suggests that females cannot predict food supply of the broodrearing period at the beginning of the season This lack of information on future food conditions seems to prevent them from accurately estimating their optimal clutch size for each season Our results suggest that individual optimization may not be a general pattern even within a species and alternative mechanisms are needed to explain clutch size variationWe thank C Müller T Marosits M Szöllösi for help in collecting data G Kékesi for assistance in the field and É Ludvig M Orell K Pearson R A Pettifor and Á Szentesi and an anonymous reviewer for statistical help or comments on the manuscript Experiments were licensed by the Pilis Park Forestry The study was funded by grants from OTKA nos 2232 17058 22014 34880

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