The dynamics of a colonization event in the European Shag: The roles of immigration and demographic stochasticity

We developed both deterministic and stochastic (through Monte Carlo simulat ions) matrix projection models to account for the relative roles of local r ecruitment and immigration in the formation and growth of a new colony of t he European Shag (Phalacrocorax aristotelis) in the western Mediterranean ( Columbretes Islands). The best fit of observed and simulated growth curves of the colony was obtained by introducing two immigration wares and taking into account demographic stochasticity;. Immigration and local recruitment of the Founder population alone cannot explain the observed growth of the;c olony. Immigrants might come from a large colony in Majorca island, approxi mately 160 km. away that declined markedly at the same time that the Columb retes colony was established. According to a sensitivity and elasticity ana lysis, changes in greater than or equal to4 veal old adult survival have th e largest impact on the population growth rate (lambda).