Bottom-up and top-down effects shaping herbivory in a tropical forest post-fire: the importance of nitrogen

• Ano de defesa: 2019
• Autor(a) principal: Queiroz, Elenir Aparecida
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Herbivoria; Incêndios florestais - Amazônia; Fogo e ecologia; Relação inseto-planta; Análise foliar; Nitrogênio; Predação (Biologia); Modelagem de equações estruturais; Ecologia Teórica
• Link de acesso: http://www.locus.ufv.br/handle/123456789/25644

Biodiversity losses have increased in tropical forests due to the use of fire to provide new areas for agricultural activities, urbanization and timber harvesting. Besides that, climate change models predict increases in forest fire occurrence in the near future. Through changes in bottom-up and top-down effects, wildfire occurrence may affect diverse ecological interactions as herbivory. The interaction influences a variety of factors in an ecosystem, mainly through changes in plant survival, productivity and growth. Thus, since frequency of fire has increased in the tropics and we do not completely understand its impact on herbivory, it is essential to know the mechanisms affecting this process in a tropical forest post-fire (bottom-up and top-down effects). In this context, we aim to determine the mechanisms that lead to increases in herbivory in a tropical forest altered by fire. Our hypothesis is that the fire severity, the abundance of chewing herbivorous insects, the abundance of predatory arthropods, the nitrogen content, and the leaf toughness, affect herbivory directly in a tropical forest. Predation test (top-down effect) was made to estimate predation in the post-fire forest, since predation influences herbivorous that in turn influence the herbivory. Samplings and the predation test were conducted in burned and unburned plots in the Amazon forest, Brazil. Leaf area analysis was performed as a measure of herbivory, and tree leaves were collected for this purpose. To determine abundance of chewing herbivorous insects and predatory arthropods, collections were made by using an entomological umbrella-beating sheet (50cm 2 ). To determine the susceptibility of plants, analysis of nitrogen content and leaf toughness measurements were performed. Finally, to estimate predation, artificial caterpillars made by modeling clay were put in trees and their attacks by predators were evaluated. To analyze herbivory and predation, a generalized linear model (GLM) was used. One-way ANOVA to analyze herbivory and regression analysis to estimate predation were performed. Structure equation modeling (SEM – path analysis) was used to see relationships among our variables and determine their impact on herbivory. Our results suggest that there is no difference between herbivory in burned and unburned plots post- fire and fire did not affect predation. Nitrogen content is the only variable measured that directly and significantly affects herbivory. Based on that, we can conclude that fire can affect herbivory indirectly through nitrogen content (a bottom-up effect) since nitrogen is known to be higher in burned areas than in unburned ones and herbivorous prefer plants with higher nitrogen content. Nitrogen is an important factor shaping herbivory in a tropical forest post-fire. Thus, understanding interactions between fire in tropical forest and ecological processes such as herbivory is important since they contribute significantly to productivity, biodiversity and ecosystem functioning.