Evol Ecol Res 5: 1223-1237 (2003)     Full PDF if your library subscribes.

The relationship between population means and variances in reproductive success: implications of life history and ecology

Juan Moreno,1* Vicente Polo,2 Juan J. Sanz,1 Ana de León,2 Eduardo Mínguez3 and José P. Veiga1

1Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales-CSIC, J. Gutiérrez Abascal 2, E-28006 Madrid, Spain,  2Division of Environmental and Evolutionary Biology, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, UK and  3Universidad Miguel Hernández, Facultad de Ciencias Ambientales, Departamento de Biología Aplicada, Av. Del Ferrocarril s/n, E-03202 Elche, Alicante, Spain

Author to whom all correspondence should be addressed.
e-mail: jmoreno@mncn.csic.es


Within populations, individuals vary in breeding performance even under identical environmental conditions. Here, we present a model of logistic improvement in reproductive success (proportion of fledglings raised per egg laid) with environmental quality for breeders with different capacities. The mean reproductive success in our model denotes environmental quality for breeding. Our model establishes a space of potential combinations of means and variances in reproductive success. In this space, positive, negative or absent trends are possible. The literature and our own long-term studies show that life-history strategies may markedly affect the sign and shape of the relationship between mean and variance in reproductive success. Populations of long-lived birds rarely achieve a high mean reproductive success, and associations between the mean and variance of breeding success in different years tend to be positive. Conversely, populations of short-lived birds present negative mean–variance relationships with high mean reproductive success and variance in good environmental conditions approaching zero. Other factors, such as resource distribution and mating system, may also affect the variance in reproductive success and mean–variance trends. Plotting means and variances in reproductive success for different years or populations may indicate important aspects of the life history and ecology of organisms.

Keywords: life history, long-term studies, mean reproductive success, parental quality, variance in reproductive success.

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