Résumé
We find the evolutionarily stable allocation of reproductive effort in both hermaphroditic and dioecious perennial plants. The model focuses on the effect of pollen availability on the allocation of reproductive effort and on sex allocation. The model shows that the effect of pollen limitation depends on the detailed assumptions made about the delivery of pollen to individual plants. We consider two extreme models: the pollen-pool model, which assumes that pollen from different individuals is mixed before being delivered, and the single-donor model, which assumes that pollen delivered to each individual comes from only one pollen donor. In the pollen-pool model, a reduction of pollen availability is equivalent to an overall reduction in fertility, while, in the single-donor model, the results are more complex and depend on the sensitivity of fertility to changes in pollen availability. The results for hermaphroditic and dioecious species are quite similar once the sex ratio of the dioecious species is taken into account.