The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama

Authors: SOLE, RAPHAELE - University Of Montpellier; GRIPENBERG, SOFIA - University Of Oxford; LEWIS, OWEN - University Of Oxford; MARKESTEIJN, LARS - Bangor University; BARRIOS, HECTOR - Universidad De Panama; RATZ, TOM - University Of Edinburgh; CTVRTECKA, RICHARD - University Of South Bohemia; BUTTERILL, PHILIP - University Of South Bohemia; SEGAR, SIMON - University Of South Bohemia; Metz, Mark; DAHL, CHRIS - University Of South Bohemia; RIVERA, MARLENY - Universidad De Panama; VIQUEZ, KARINA - Universidad De Panama; FERGUSON, WESSLEY - Universidad De Panama; GUEVARA, MAIKOL - Universidad De Panama; BASSET, YVES - Universidad De Panama

Submitted to: Nature Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2019
Publication Date: 3/6/2019
Citation: Sole, R., Gripenberg, S., Lewis, O.T., Markesteijn, L., Barrios, H., Ratz, T., Ctvrtecka, R., Butterill, P.T., Segar, S.T., Metz, M., Dahl, C., Rivera, M., Viquez, K., Ferguson, W., Guevara, M., Basset, Y. 2019. The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama. Nature Conservation. 32:81-101.

Interpretive Summary: The bay cedar tree is an important species in Central American agroforestry. This study investigated the impact of seed- and seedling-feeding insects on the regeneration of bay cedar communities. The findings suggest that early seeds are most susceptible to insect damage, but insect damage is less of a concern than inclement weather.

Technical Abstract: A significant proportion of the mortality of rainforest trees occurs during early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazuma ulmifolia (Malvaceae), an important tree species in agroforestry in Central America. We reared predispersal insect seed predators from G. ulmifolia seeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G. ulmifolia seeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits of G. ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible postdispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (>95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G. ulmifolia at our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow.