DOES REPRODUCTIVE SUCCESS INCREASE WITH AGE OR WITH SIZE IN SPECIES WITH INDETERMINATE GROWTH - A CASE-STUDY USING SAND LIZARDS (LACERTA-AGILIS)

Most data on determinants of reproductive success (RS) and reproductiv e ''tactics'' are correlational in nature, and hence cannot be used to infer causation. Consistent patterns - such as an increase in RS with age, as seen in many types of organisms - may result from diverse und erlying mechanisms. Ontogenetic increases in RS in mammals and birds m ay be due largely to direct effects of age (via learning, etc.) but ou r analyses show that apparently analogous ontogenetic shifts in reprod uctive tactics and increases in RS in sand lizards (Lacerta agilis) ar e actually due to ontogenetic changes in body size. When size effects are removed, age exerts very little effect on either reproductive beha viour or RS in either sex. In many taxa, both age and body size may ex ert important effects on reproductive biology, and disentangling these effects should be a focus of further research.