Avian invasions: from basic to applied research.

Abstract

Serious concern for environmental and economic problems caused by biological invasions has caused a huge interest in trying to understand the factors that influence the invasive process. This information is essential to prevent, assess, and mitigate the impacts of invasive species. In this context, this thesis has two main goals. The first is to ask what makes a species a successful invader, and second to investigate whether this information can be useful for preventing the impact of the invaders. This thesis explores these questions using birds as the object of study. To understand why exotic species, whose initial populations are generally small and genetically depleted, can sometimes succeed to establish themselves in environments to which they have had no opportunity to adapt it has often been invoked that successful invaders have adaptations that allow them to overcome these problems. Ecological theory suggests that life histories should be part of these adaptations. The characteristics of the species related to reproduction and survival should play an important role in reducing the risk of extinction by stochastic factors at the initial stages of the invasion process. The results indicate that successful invaders are characterized by prioritizing future over current reproduction, probably because a great success in reproducing in the future reduces the cost of reproductive failure under conditions of uncertainty and increases the opportunities to explore and respond to new environmental pressures. In addition, alien species should have adaptations to find an appropriate niche to survive in and prosper, to avoid extinction by negative population growth. This niche should include not only necessary resources, but also few competitors and enemies. Theory suggests two ways to achieve this niche: or invasive species are competitively superior and displace native species from their current niches, or invaders are opportunistic and have the ability to find unused ecological niches. In this thesis the relative importance of these two hypotheses has been contrasted trough the study of the invasion of the Red-billed Leiothrix (Leiothrix lutea) in the Collserola forest reserve. The invader established with relatively little resistance from the native species, reflecting its generalist and opportunistic nature and that its ecological requirements were underrepresented in the native community. However, there has been a decline of a native species ecologically similar to the invader during the period of expansion, presumably due to competitive displacement. These results show that both hypotheses are not mutually exclusive, but taken together can help to better understand of the establishment process. Finally, this thesis asks whether it is possible to use the species features proposed to be related to the invasive success to develop a methodology to detect potentially invasive species and, thus, to be able avoid future problems. The results show that invasive success can be predicted by the founder population size, habitat use, brain size, and the ability of species to prioritize future reproduction. Although there are few traits, the models predicted the probability of successful establishment for birds in Europe and Australia with high accuracy. Therefore, it is demonstrated that risk assessments based on characteristics related to the success of the establishment are difficult but feasible and provide a useful tool for guiding preventive polices aimed at mitigating the impact of invasive species. However, this thesis also shows that, to be fully effective, these methods have indeed to be applied in the environmental management policies if we really want to avoid a future dominated by invasive species.

Date of Award	25 May 2012
Original language	English
Supervisor	Daniel Sol Rueda (Director)