Frugivores and cheap fruits make fruiting fruitful.

Animal seed dispersal provides an important ecosystem service by strongly benefiting plant communities. There are several theoretical studies on the ecology of plant-animal seed-disperser interactions, but few studies have explored the evolution of this mutualism. Moreover, these studies ignore plant life history and frugivore foraging behaviour. Thus, it remains an open question what the conditions for the diversification of fruit traits are, in spite of the multitude of empirical studies on fruit trait diversity. Here, we study the evolution of fruit traits using a spatially explicit individual-based model, which considers the costs associated with adaptations inducing dispersal by frugivory, as well as frugivore foraging behaviour and abundance. Our model predicts that these costs are the main determinants of the evolution of fruit traits and that when the costs are not very high, the evolution of larger fruit traits (e.g. fleshy/colourful fruits) is controlled by the choosiness and response thresholds of the frugivores as well as their numerical abundance.

Resource competition in stage-structured populations.

Two models are made to account for the dynamics of a consumer-resource system in which the consumers are divided into juveniles and adults. The resource grows logistically and a type II functional response is assumed for consumers. Resource levels determine fecundity and maturation rates in one model, and mortality rates in the other. The analysis of the models shows that the condition for establishment of consumers is that the product of per capita fecundity rate and maturation rates is higher than the product of juvenile and adult per capita decay rates at a resource level equal to its carrying capacity. This result imposes a minimal abundance of resource able to maintain the consumers. A second result shows an equilibrium stage structure, with a small instability when juveniles and adults mean saturation constants are different. The implications of these results for community dynamics are discussed.