Acknowledgments

I am grateful to Emiel van Loon for the comments and suggestions that help the improvement of this work, to Muriel Perez, W. Daniel Kissling and Kasper Abcouwer for helpful discussions and to the Ecuadorian Secretary for Superior Education, Science, Technology and Innovation (Senescyt)[http://www.educacionsuperior.gob.ec/] for funding my MSc. studies through the scholarship “Convocatoria Abierta 2014 I fase”