Is the inverse leafing phenology of the dry forest understory shrub Jacquinia nervosa (Theophrastaceae) a strategy to escape herbivory?

ABSTRACT

In the dry forest of Santa Rosa National Park, Costa Rica, the understory shrub Jacquinia nervosa presents an inverse pattern of phenology that concentrates vegetative growth and reproduction during the dry season. In this study, we tested the [quot ]escape from herbivory[quot ] hypothesis as a potential explanation for the inverse phenological pattern of J. nervosa. We monitored leaf, flower and fruit production in 36 adult plants from October 2000 to August 2001. Leaves of six randomly selected branches per plant were marked and monitored every two weeks to measure the cumulative loss in leaf area. To analyze pre-dispersal seed predation we collected 15 fruits per plant and counted the total number of healthy and damaged seeds, as well as the number and type of seed predators found within the fruits. Leaf, flower, and fruit production occurred during the first part of the dry season (end of November to February). The cumulative herbivory levels were similar to those observed in other tropical dry forest tree species that concentrate leaf production during the wet season, and were concentrated on young leaves, which lost an average of 36.77 % of their area (SD = 34.35 %, N = 195). Chewing beetles of the genus Epicauta (Meloidae) were the most important herbivores. In mature leaves, most of the damage was caused by the beetle Coptocycla rufonotata (Chrysomelidae). Fruits took 4 months to develop during the dry season (January-March 2001) but continue increasing in size well into the first 3 months of the wet season (May-July). Average seed number per ripe fruit was 9 (SD = 5, N = 500). Seed predation in mature fruits was 42 % (SD = 47 %, N = 122). Most seeds were damaged by moth larvae of the family Tortricidae. Only 3 % of the flowers became fruits. This was influenced by the low level of flower synchrony (0.38+/-0.26, N = 36 plants), but neither leaf synchrony (0.88+/-0.06, N = 36 plants) nor plant size influenced fruit numbers. The significa...

RESUMEN

Analizamos la hipótesis de “escape de la herbivoría” como explicación para la fenología foliar inversa del arbusto de sotobosque del bosque seco Jacquinia nervosa, el cual produce sus hojas durante la estación seca y se mantiene sin ellas durante la estación lluviosa. Medimos la producción de hojas, flores y frutos, el daño por herbivoría en hojas y semillas, y la fauna de herbívoros en 36 plantas adultas de octubre del 2000 a agosto del 2001 en Santa Rosa, Costa Rica. La herbivoría foliar acumulada durante la estación seca fue similar a la herbivoría de otras especies que concentran la producción foliar en la estación lluviosa. En las hojas maduras la mayor parte del daño fue causado por el escarabajo Coptocycla rufonotata (Chrysomelidae). La depredación de semillas predispersión fue de 42 % (DE= 47 %, N= 122) y es causada por larvas de polilla de la familia Tortricidae. Los niveles de daño indican que la fenología foliar de J. nervosa no coincide con la hipótesis de “escape”. Considerando la fuerte estacionalidad del bosque seco y el carácter heliófito de J. nervosa, es probable que esta estrategia fenológica evolucionara en respuesta a cambios estacionales en la disponibilidad y calidad de la luz, y duración del fotoperíodo.