Factors influencing Soay sheep survival

被引:100
作者
Catchpole, EA
Morgan, BJT
Coulson, TN
Freeman, SN
Albon, SD
机构
[1] Univ Kent, Inst Math & Stat, Canterbury CT2 7NF, Kent, England
[2] Australian Def Force Acad, Canberra, ACT, Australia
[3] Zool Soc London, Inst Zool, London NW1 4RY, England
[4] British Trust Ornithol, Thetford, England
[5] Inst Terr Ecol, Banchory, Kincardine, Scotland
关键词
integrated analysis; logistic regression; mark recapture; mark recovery; maximum likelihood; Soay sheep; survival;
D O I
10.1111/1467-9876.00205
中图分类号
O21 [概率论与数理统计]; C8 [统计学];
学科分类号
020208 ; 070103 ; 0714 ;
摘要
We present a survival analysis of Soay sheep mark recapture and recovery data. Unlike previous conditional analyses, it is not necessary to assume equality of recovery and recapture probabilities; instead these are estimated by maximum likelihood. Male and female sheep are treated separately, with the higher numbers and survival probabilities of the females resulting in a more complex model than that used for the males. In both cases, however, age and time aspects need to be included and there is a strong indication of a reduction in survival for sheep aged 7 years or more. Time variation in survival is related to the size of the population and selected weather variables, by using logistic regression. The size of the population significantly affects the survival probabilities of male and female lambs, and of female sheep aged 7 or more years. March rainfall and a measure of the North Atlantic oscillation are found to influence survival significantly for all age groups considered, for both males and females. Either of these weather variables can be used in a model. Several phenotypic and genotypic individual covariates are also fitted. The only covariate which is found to influence survival significantly is the type of horn of first-year female sheep. There is a substantial variation in the recovery probabilities over time, reflecting in part the increased effort when a population crash was expected. The goodness of fit of the model is checked by using graphical procedures.
引用
收藏
页码:453 / 472
页数:20
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