The scaling of seed size

1. Rees & Venable (2007; Journal of Ecology , 95 , 926–936) critically evaluated ideas of Moles et al. to explain the cross-species positive correlation between offspring size and adult size, arguing that they had misinterpreted the theoretical literature, and used cross-species patterns to constrain the evolution of life-histories. 2. In a reply to Rees & Venable, Westoby et al. (2009; Journal of Ecology , 97 , 23–26) claimed we had misrepresented their views. Here we try to clarify the arguments indicating points of agreement and disagreement. 3. Using simple models we then extend the current theory to allow (i) the time during which seedling survival is influenced by seed mass to scale with the duration of the juvenile period and (ii) the intensity of stress experienced by seedlings to scale with adult size. These new models predict that species with long juvenile periods or large adult size will have larger seeds. 4. We synthesize the new theoretical ideas with our current understanding of the evolution of seed mass, and suggest that much of the observed increase in seed mass with adult body size may be due to constraints correlated with adult body size.