Variability within families and the evolution of body-condition-dependent dispersal.

In a population where body condition varies between and within families, we investigate the evolution of dispersal as a function of body condition ('strength', e.g. body size). Strong individuals are better competitors in a weighted lottery. If body condition does not influence survival during dispersal, then there is no unique evolutionarily stable strategy. Instead, there are infinitely many dispersal strategies that all lead to the same non-dispersing weight in a patch. These strategies are all selectively neutral but determine wildly different relationships between body condition and disposal probability. This may explain why there is no consistent pattern between body condition and dispersal found in empirical studies. If body condition influences survival during dispersal, then neutrality is removed and individuals with higher survival probability disperse. Dispersal may be the competitively weaker individuals if smaller body size helps to avoid dispersal risks.