Behavior may be dramatically influenced by changing environments, and differences in light intensity environments may have important behavioral consequences. One approach to understanding changes in behavior is by studying behavioral syndromes, suites of correlated behaviors reflecting between individual consistencies in behavior expressed within a behavioral situation (e.g., correlations between antipredator behaviors in different habitats), or across behavioral contexts (e.g., correlations among feeding, antipredator, or mating behavior) (Sih et al. 2004a). Guppies (Poecilia reticulata) provide a great model system to study behavior. Guppies are small, freshwater tropical fish that inhabit still pools in swift-flowing streams, and the backwaters of small rivers in mountain forest areas of Trinidad (Houde 1997; Magurran 2005). In this study I attempted to answer the following questions using three low predation populations of guppies : 1) Do guppies display a behavioral syndrome for aggression and/or courtship across light situations?; 2) Are there mean level changes in aggression or courtship across light situations?; 3) Are mean level changes influenced by differing social environments that include or lack sexually receptive females?; 4) Are there correlations between behavior and the androgen hormones testosterone and 11-ketotestosterone?; 5) Are there correlations between behavior and the stress hormone cortisol?; 6) Are there mean level changes in hormone release rates across light environments?; and 7) Is flexibility in hormone release rates influenced by social environments that include or lack sexually receptive females? Guppies exhibit behavioral syndromes for both aggression and courtship. Furthermore, guppies exhibit behavioral flexibility for both aggression and courtship, but only in social environments that include sexually receptive females. I found no correlations between behavior and androgen hormones. I also did not find any correlations between behavior and the stress hormone cortisol. Furthermore, I did not find any mean level changes in hormone release rates across light environments. Interestingly, cortisol levels were higher in social environments in which sexually receptive females were absent. Many studies have looked at how the environment influences courtship behavior in guppies, especially employing high predation populations, but few studies have examined aggressive behavior or behavior in general with low predation populations. Furthermore, few studies have determined the role social environments play, and how hormones may interact with behavior. This study is important because it helps illuminate how low predation populations deal with changes in light intensity environments, and adds to what we understand about guppy behavior in general.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The Semideciduous Seasonal Forests receive this name because they lose 20 to 50% of their leaves during the dry season. They are typical formations of the Central Brazil, and they present high diversity of vegetable species with approximately 180 vascular species per hectare. However, these forests are currently found only as small fragments. The study of these remaining becomes important to better understand, and thus preserve and recover these forests. Siparuna guianensis Aublet. and Inga sessilis Vell. (Mart.) are characteristic species of such formations and present a great potential for the conservation of them and for the enrichment and the recovery of degraded areas due to their great environmental plasticity. In this study were measured the natural regeneration of these two species in two different microenvironments, natural canopy gaps and areas under closed canopy. A higher density of S. guianensis was found in canopy gaps, decreasing with the increase of these areas. The closed canopy areas and the large canopy gaps seem to present a limiting luminous condition for this species. The herbivory in these species, another factor that influences the natural regeneration, was also estimated in both microenvironments. It was found a greater herbivory rate unique and precisely in individuals of S. guianensis of canopy gaps. This difference was not explained by the nutritional quality of their leaves, which may then be explained by the greater amount of food available to this specie s herbivores in these areas (canopy gaps). Moreover, the photosynthetic responses of S. guianensis and I. sessillis were measured in different microenvironments during the dry season. The results found proved the high environmental plasticity of these species, since despite the water scarcity and the high radiation, there was no occurrence of chronic photoinhibition in selected individuals, but photosynthetic adaptations for dissipation of the excess, potentially harmful, of luminous energy. Presenting the individuals located under the canopy gaps a greater photosynthetic performance probably because they are early successional species, benefit from the conditions of this microenvironment. / As Florestas Estacionais Semideciduais recebem este nome porque perdem 20 a 50% de suas folhas durante a estação seca. Elas são formações típicas do Brasil Central e apresentam alta diversidade de espécies vegetais, com cerca de 180 espécies vasculares por ha. Entretanto, atualmente, essas florestas encontram-se apenas como pequenos fragmentos. O estudo destes remanescentes torna-se importante para melhor conhecer e, assim, preservar e recuperar estas florestas. Siparuna guianensis Aublet. e Inga sessilis Vell. (Mart.) são espécies características dessas formações e apresentam grande potencial para a conservação destas e para o enriquecimento e recuperação de áreas degradadas devido a sua grande plasticidade ambiental. Neste estudo foi levantada a regeneração natural destas duas espécies em dois diferentes microambientes, clareiras naturais e áreas sob dossel fechado. Foi encontrada uma maior densidade de S. guianensis nas clareiras, decrescendo com o aumento da área destas. As áreas de dossel fechado e as maiores clareiras apresentaram, pelo que parece, uma condição luminosa limitante para esta espécie. A herbivoria nessas espécies, outro fator que influencia a regeneração natural, também foi estimada, nos dois microambientes. Foi encontrada uma maior taxa de herbivoria, única e justamente nos indivíduos de S. guianensis de clareiras. Essa diferença não foi explicada pela qualidade nutricional de suas folhas, podendo ser, então, explicada pela maior quantidade de alimento disponível para os herbívoros desta espécie nessas áreas (clareiras). Além disso, foram medidas as respostas fotossintéticas de S. guianensis e I. sessilis nos diferentes microambientes durante a estação seca. Os resultados encontrados comprovaram a alta plasticidade ambiental dessas espécies, uma vez que, apesar da escassez de água e das altas radiações, não foi observada a ocorrência de fotoinibição crônica nos indivíduos selecionados, e sim, adaptações fotossintéticas para a dissipação do excesso, potencialmente prejudicial, de energia luminosa. Apresentando os indivíduos localizados sob as clareiras um maior rendimento fotossintético, provavelmente por se tratar de espécies de início de sucessão, beneficiadas pelas condições desse microambiente. / Mestre em Ecologia e Conservação de Recursos Naturais