| Summary: | Tese de mestrado. Biologia (Biologia da Conservação). Universidade de Lisboa, Faculdade de Ciências, 2007 Invasive species are viewed as one of the most significant causes of biodiversity loss. Introduced feral cat populations in particular, are an important threat to many island vertebrate populations, namely to seabirds. Release of a parasite as the Feline Immunodeficiency Virus (FIV) in these mostly immune-naïve populations is thought to be an efficient control measure. Such an approach is theoretical investigated here, using mathematical models that describe the potential effects of introducing FIV into the cat population on the dynamics of simple food webs. The consequences of virus introduction were addressed using either a bi-trophic system, comprising an indigenous prey (birds) and an introduced superpredator (cats), or a tri-trophic system comprising additionally an introduced mesopredator (rodents). Results show that FIV cannot fully eradicate cat populations on sub-Antarctic islands, but can be an efficient agent for their long-term control. As a consequence endangered prey may recover from such control as they are expected to increase their population level. However, this study emphasis that despite of being counter-intuitive, the control of superpredators by virus introduction, thought to be less brutal, is not always the best solution to protect endemic prey. Several harmful effects can emerge after virus introduction. It can either induce the destabilization of the community or cause the so-called mesopredator release effect, a burst of mesopredators following superpredators’ control. Both types of mesopredator release phenomena, the severe and the mild release, mentioned in the literature are possible outcomes on more complex ecosystems. Understanding the key trophic interactions before any control attempt is of crucial importance otherwise the consequences of such conservation effort can be devastating. Despite its potential as an important tool in conservation biology, virus introduction ...
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