Examinando por Autor "Lewis, Owen T."

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Increased mortality of tropical tree seedlings during the extreme 2015–16 El Niño
(Wiley, 2021-07-17) Browne, Luke; Markesteijn, Lars; Engelbrecht, Bettina M. J.; Jones, F. Andrew; Lewis, Owen T.; Manzané‐Pinzón, Eric; Wright, S. Joseph; Comita, Liza S.
As extreme climate events are predicted to become more frequent because of global climate change, understanding their impacts on natural systems is crucial. Tropical forests are vulnerable to droughts associated with extreme El Niño events. However, little is known about how tropical seedling communities respond to El Niño–related droughts, even though patterns of seedling survival shape future forest structure and diversity. Using long-term data from eight tropical moist forests spanning a rainfall gradient in central Panama, we show that community-wide seedling mortality increased by 11% during the extreme 2015–16 El Niño, with mortality increasing most in drought-sensitive species and in wetter forests. These results indicate that severe El Niño–related droughts influence understory dynamics in tropical forests, with effects varying both within and across sites. Our findings suggest that predicted increases in the frequency of extreme El Niño events will alter tropical plant communities through their effects on early life stages.
The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama
(Pensoft Publishers, 2019-02-06) Solé, Raphaële; Gripenberg, Sofia; Lewis, Owen T.; Markesteijn, Lars; Barrios, Héctor; Ratz, Tom; Ctvrtecka, Richard; T. Butterill, Philip; T. Segar, Simon; A. Metz, Mark; Dahl, Chris; Rivera, Marleny; Viquez, Karina; Ferguson, Wessley; Guevara, Maikol; Basset, Yves
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 pre-dispersal 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 post-dispersal 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.