A seven-year study of individual variation in fruit production in tropical bird-dispersed tree species in the family Lauraceae

Abstract

Fruit crop sizes varied from year to year among 22 sympatric, bird-dispersed tree species in the Lauraceae. Each species in the lower montane forests of Monteverde, Costa Rica fruited at a characteristic season, but there was wide yearto-year variability in the porportion of each population that produced fruit and in the average size of fruit crops. Over a 7-year period (1979-1985), overall fruit production was high during three nonconsecutive years and low during four years. Within genera, tree species displayed distinct fruiting schedules. Even within populations, individual trees sometimes fruited in different years or failed to fruit altogether. Yearly rainfall and temperature patterns did not explain annual variation in fruit production. Unexpectedly, neither did previous reproductive histories: there was little correlation between an individual tree’s fruit production in a given year and its fruit production the previous year. On the other hand, vegetative growth was negatively correlated with reproduction in 12 of 15 species. Lauraceous fruits make up 60–80% of all fruits eaten by bird species such as Three-wattled Bellbirds and Resplendent Quetzals. These birds may respond to annual variation in the availability of lauraceous fruits by migrating locally, by expanding their diets to include previously ignored foods or unripe fruits, or by delaying breeding.