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Universidad de Buenos Aires (2012)

Effects of granivory/herbivory on tree invader species in grasslands of the inland pampa

Muschetto, Emiliano

Titre : Effects of granivory/herbivory on tree invader species in grasslands of the inland pampa

Efectos de la granívora/herbivoría sobre la invasión de especies leñosas en pastizales de la pampa interior

Auteur : Muschetto, Emiliano

Université de soutenance : Universidad de Buenos Aires

Grade : Doctor en el área de Ciencias Biológicas 2012

Biological invasions are one of the processes that are contributing to the loss of diversity in many systems ; although the magnitude of the effect depends on the characteristics of the invaded communities and the presence of natural enemies. In this context, the general objective of this thesis was to advance in the knowledge of the role of small rodents in the resistance to tree species invasion, particularly G. triacanthos and R. pseudoacacia, in the Pampas region. A rodent exclusion experiment of 4-year duration, which included disturbances generation to simulate early successional stages, showed that both the effect of rodents and disturbances varied depending on the woody species considered. Rodents only had a positive effect on the germination of G. triacanthos in disturbed plots and had no effect on the mortality of seedlings. The disturbances affected only G. triacanthos seedlings, decreasing the mortality in the first year of study and then causing an increase in the last year, when there was a change in the dominant plant species of the community. Precipitations during the growing season of the seedlings affected the chances of invasion of both woody species and also affected the rodent population. G. triacanthos seeds remained viable in the seed bank during a longer period than those of R. pseudoacacia. The comparison of seed removal along seasons and in plant communities that differed in structure and alternative food availability showed higher consumption in the season where rodents recorded greater abundances (autumn) and varied according to study sites. Alternative food availability would be the main factor explaining differences in seed predation, mainly through indirect interactions like apparent mutualism. In turn, the experiments under controlled conditions determined that rodents would decrease the consumption of G. triacanthos seeds in the presence of alternative food composed by native and exotic herbaceous seeds of small size. The results of this thesis suggest that the invasion success of woody species would be given by the interaction between extrinsic factors (fluctuations in environmental conditions) and those intrinsic of plant communities and rodent populations.


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