Plant/frugivore interactions in South American temperate forests. Interacciones planta/frugfvoro en bosques templados de Sudamerica

Berry- and nut-bearing plant species comprise more than 70% of the flora in mediterranean shrublands as well as in temperate rain forests in Chile. We examine the role of fruit-eating animals as seed dispersers in South American temperate forests. Among the mammals, foxes (genus Dusicyon) are reported to be major dispersers of the seeds of several native plants, especially during summer and fall. A small deer (Pudu pudu) and an arboreal marsupial (Dro­ miciops australis) are also fruit eaters, but their role as seed dispersers is unclear. The most important frugivores in South American temperate forests, in terms of species richness, numbers of individuals, and activity, are birds. A total of 17 species of birds consume fleshy fruits. They all have a mixed diet, feeding on fruits and insects, although six species feed primarily on fruit. Several species of avian frugivores are reported to be migratory, but we know little about their seasonal patterns of abundance and their routes of migration. We discuss a case study of the interaction between fruit-eating birds and plants in the temperate rain forest of Chiloe (42°S, 74°W). Color and size characteristics of fleshy fruits were analyzed in relation to fruit consumption by birds. Black-colored fruits predominated among trees, whereas most shrubs had red fruits. Black hues might be UV-signals to birds in dark forest interiors. Average diameter of fruits (8.93 mm) closely matched the average gape width of frugivorous birds (8.62 mm), but there were several plant species with fruit sizes greater than the widest gape of a forest bird. This differs from the pattern shown for other forests, in the tropics and the north-temperate region, where the distribution of fruit sizes is included within the range of bird gape widths. We suggest that the Quaternary history of disturbances and extinctions in south-temperate forests may have caused some plants to lose their original seed dispersers. Finally, we dicuss the applicability of Herrera's Relative Yield (RY) index for estimating the potential profitability of fruits to birds. An alternative to this index, based on the ratio between pulp dry mass and fruit dry mass, rather than fresh mass as in RY, is proposed as a more suitable estimator of profitability for fruits