Ecologia
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/182
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Resultados da Pesquisa
Item Importance of chemical and geographical distances in determination of ant’s aggressive behavior: first insight in the Cecropia-Azteca system(Universidade Federal de Viçosa, 2019-02-27) Neves, Gabriela Zorzal; Campos, Ricardo Ildefonso de; http://lattes.cnpq.br/3679330638283908Territorial animals respond less aggressively to intrusions by neighbors than by outsiders. This difference in behavioral responses is termed “dear-enemy phenomenon” and it determines recognition and aggressiveness in animal interactions. In social insects, the identification of non-nest mates is mainly performed through "colony odors", formed by hydrocarbon lipid compounds that cover the insects’ cuticle (also called CHCs). The difference in the chemical composition of these compounds may be genetically influenced and influenced by the environment and/or by the diet of colony individuals. Myrmecophytic ants present an aggressive defensive behavior against plants natural enemies. These systems might be considered a promising model for studying nest-mate recognition and aggressiveness behaviors. Thus, the present study aims to experimentally test the importance of geographical and chemical distances on the aggressive behavior among individuals of Azteca muelleri ants inhabiting Cecropia glaziovii plants. We sampled a total of 50 ant colonies in three Atlantic Forest fragments located in the Viçosa municipality, state of Minas Gerais, Brazil. The distance in meters between sites were estimated using the GPS data provided from the two points of interest. After sampling, we performed aggression tests using five works from the same colony against five workers from other colony. Each colony was used only once. For the aggression tests we divided the 50 colonies in two distinct groups: same location group and different location group. Then, we observed the behaviors of ants in each aggression test and we classify them as non-aggressive and as aggressive. After the aggression tests, we identified picks of chemicals compounds (CHCs) and evaluated the concentrations of these components by chemical analysis. Our results showed a positive effect of geographical distance on ant aggressiveness and a significantly higher aggressiveness between pairs of ants from different site when compared to pairs of ants belonging to the same site. On the other hand, A. muelleri aggressiveness was not influenced by chemical cuticles profile and we alsov did not detect a significant interaction between geographical distance and chemical distance. The Azteca-Cecropia system therefore exemplifies a relationship in which the geographic distance influences the aggressive behaviour. However, in this system the total of chemical compounds does not explain the aggression behaviour and only some these compounds may play a main role in the aggressive behaviour and non-nest mate recognition. Thus, it is necessary to investigate if these factors and others parameters such as genetic distance, may be influencing the aggressive behaviour in this species of Azteca.Item Bottom-up and top-down effects shaping herbivory in a tropical forest post-fire: the importance of nitrogen(Universidade Federal de Viçosa, 2019-02-28) Queiroz, Elenir Aparecida; Schoereder, José Henrique; http://lattes.cnpq.br/6361847773845991Biodiversity 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.Item Testing the influence of the myrmechocory on seed fate and plant establishment(Universidade Federal de Viçosa, 2018-02-28) Fernandes, Tiago Vinícius; Campos, Ricardo Ildefonso de; http://lattes.cnpq.br/1836811756076898Ants are considered one of the most remarkable invertebrates to disperse seeds. Seed dispersion by ants (myrmecochory) can be divided in three main phases: i) Removal; ii) Manipulation and iii) Deposition. However, all three phases have never been tested simultaneously and the contribution of each one on seed fate and seedling establishment remains unknown. In this purpose, our main aim was to determine experimentally and in field conditions the separate effect of each myrmechocory’s phase on the most critical plant stages: seed germination and seedling establishment. We choose as model organisms, the myrmecochous tree Mabea fistulifera and the leaf-cutting ant Atta sexdens. To simulate the effect of removal we used 30 distances of from the closest conspecific adult tree. To test the manipulation, in each distance we set three seed treatments levels manipulated by A. sexdens in laboratory: unmanipulated, non-scarified/without elaiosome, and scarified/without elaiosome. Finally, to test the deposition effect, we placed seed treatments over and away from ant nests. We evaluate seed germination for 90 days and seedling growth and survival for a year. We found that the increase in distance from the closest M. fistulifera adult tree decreases seed germination and increases seedling growth but have no effect on seedling survival. Moreover, neither the nest environment nor ant manipulation treatments affect seed germination, seedling growth, and survival. We experimentally showed in field conditions the role of myrmecochorous seed distancing from conspecific plants. Moreover, we suggest a life history conflict on this plant, associate to seed distancing that impairs seed germination and beneficiate seedling growth.Item Nicho trófico de grilos de serrapilheira florestal: uma análise utilizando isótopos estáveis de carbono e nitrogênio(Universidade Federal de Viçosa, 2015-09-29) Jesus, Fabiene Maria de; Sperber, Carlos Frankl; http://lattes.cnpq.br/5222507542999786Vários mecanismos propostos por ecólogos teóricos buscam elucidar os processos envolvidos na coexistência de espécies em comunidades biológicas. Dentre esses mecanismos destacam-se aqueles que preveem a coexistência de espécies sendo facilitada por uma partição de recursos, associando processos competitivos à teoria de nicho. Assim, a coexistência e as interações entre as espécies têm sido investigadas por meio dos conceitos de nicho postulados e revisados por diversos estudiosos. Alguns autores têm proposto uma abordagem metodológica e tecnológica relativamente nova baseada em análise de isótopos estáveis (AIE), que pode ser utilizada para medir algumas das muitas dimensões dos nichos ecológicos. Neste contexto, a utilização da AIE em tecidos animais está permitindo descrever nichos isotópicos, cujos eixos em um espaço multidimensional seriam diferentes assinaturas isotópicas (por exemplo, δ 15 N e δ 13 C). A utilidade da AIE reside no fato de que os tecidos em expansão apresentam grandes variações temporais de δ 15 N e δ 13 C que refletem diretamente a gama de recursos alimentares consumidos e isotopicamente contrastantes ao longo do tempo. No entanto, estudos que utilizam AIE para estimar nicho trófico exigem o conhecimento de alguns fatores que podem alterar os valores isotópicos de δ 15 N e δ 13 C em tecidos animais, tais como: (i) os tipos de preservação que as amostras são submetidas antes da análise; (ii) o fracionamento isotópico que ocorre em tecidos de consumidores com relação a sua dieta. Neste contexto, esta tese apresenta três capítulos. No primeiro capítulo, nosso objetivo foi estabelecer uma metodologia que preservasse amostras de grilos para posterior AIE sem que houvesse alterações nos valores de δ 15 N e δ 13 C. Para isso, nós comparamos amostras de grilos recém processadas (controle) com amostras submetidas a dois métodos de preservação: físico (congelamento) e químico (etanol comercial e combustível) por 15 e 60 dias. Nossos resultados indicam que todos os métodos de preservação testados alteram pelo menos um dos valores isotópicos dos grilos quando comparado com o controle. Assim, recomendamos o uso de material recém-processado para AIE em grilos. No segundo capítulo, nosso principal objetivo foi avaliar como se dá o fracionamento dos valores isotópicos de δ 13 C e δ 15 N encontrados em corpos de grilos alimentados com dieta artificial e com isso fornecer informações de base para interpretar resultados de nicho trófico baseados na AIE de grilos em comunidades biológicas. Para isso, estimamos os valores isotópicos de δ 13 C e δ 15 N de indivíduos de três espécies de grilos alimentados com dieta artificial, e comparamos com os valores isotópicos da dieta artificial. Estimamos também os valores isotópicos de δ 13 C e δ 15 N encontrados em corpos de grilos alimentados em campo (dieta natural desconhecida). Nós demonstramos que a AIE é uma ferramenta promissora para investigar a posição trófica dos grilos de serrapilheira, uma vez que temos estimativas do quanto o 15 N varia nos grilos com relação à sua dieta. E por último, no terceiro capítulo descrevemos o nicho trófico da comunidade de grilos, avaliando a partição de nicho entre espécies coocorrentes de grilos. Encontramos evidências de que a coexistência de espécies de grilos em comunidades naturais envolve partição de recursos alimentares. O local de forrageamento influenciou diretamente no uso da dieta e conseqüentemente na posição trófica dos grilos, os quais apresentaram até três níveis tróficos quando avaliados em um contexto global da dieta. Essa partição é evidenciada pelos diferentes valores de δ 15 N encontrados nos corpos dos grilos. Os valores de δ 13 C evidenciam que os grilos utilizam recursos alimentares com origem em plantas C 3 . Finalmente, encontramos evidências de estreitamento do nicho trófico à medida que aumenta o número de espécies coocorrentes.