The contribution of a naturalized tropical tree to bird diet & seed dispersal in secondary forest fragments

Abstract

Thousands of plant species have been introduced worldwide as the result of human activity. Some of these plant species have become naturalized, meaning they can establish new, self-sustaining populations without assistance and have become incorporated with the resident flora. Psidium guajava (Myrtaceae) was introduced to Brazil from Mexico by pre-Columbian people and is now considered naturalized. While an important food source for some native Brazilian fauna, P. guajava may pose a threat to plant diversity as introduced species have the potential to become invasive. Introduced species like P. guajava are especially prevalent in naturally regenerating secondary forests, which have become increasingly common as abandoned lands recover. The presence of introduced species combined with human mediated changes like surrounding land-use create the potential for novel plant-animal interactions and novel communities as a whole within these secondary forests. Due to the novelty of this ecosystem type, plant-animal interactions involving introduced species currently form a major knowledge gap. The fragmented nature of these secondary forests makes understanding the role P. guajava plays within bird seed dispersal and as a food resource to birds especially important due to their long dispersal distances. Our project will capture a comprehensive image of the role of P. guajava by analyzing seed dispersal from both the plant and bird perspective. In this proposed study, we will quantitatively evaluate how effective seed dispersal of P. guajava is as well as how effective different bird species are as seed dispersers (plant perspective) and how important P. guajava is to bird diet (bird perspective). We plan on working in plots established by Pedro Brancallion's team in the Corumbataí river basin, which vary in forest age, P. guajava abundance, and total zoochorous woody plant species diversity. We will use a combination of focal observations of birds feeding on P. guajava, phenology surveys, and mist netting to collect bird droppings, in order to answer these questions. While our project foundation will be built upon established methods, we will also develop a novel protocol to extract DNA from bird droppings to detect when guava is present in bird diet. From these data, we will determine which forest and bird characteristics result in the most quantitatively effective seed dispersal of P. guajava and gain a better understanding of the role this naturalized tropical tree plays in secondary forests. (AU)