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Biological invasions lead to loss of biodiversity and ecosystem degradation, and a better understanding of their drivers is urgently needed. This is particularly true in the initial stages of an invasion, when the transition from local establishments to regional advancing fronts occurs. The abundances of the local population, demographic rates, and spatial conditions for dispersal have been proposed to interact in determining invasive species expansion, but little empirical evidence has been accumulated. This study examines the population dynamics of the American bullfrog (Aquarana catesbeiana), a globally invasive aquatic anuran, during the initial stages of its invasion process in a pond landscape within the Pampas grasslands of Uruguay. We evaluated how the spatial spread of the invasion was influenced by connectivity between invaded and uninvaded ponds, bullfrog abundance in invaded ponds, elevation gradients, and pond area. This analysis was based on an 11-year monitoring program (2012-2022) that captured the onset and initial stage of spatial expansion. Throughout the study period, the number of invaded ponds increased at a rate of 7.7 % per year. A model of invasion probability revealed that connectivity to invaded ponds and the population status of those ponds were key determinants of spread. Connectivity to previously invaded ponds interacted with bullfrog abundance to determine invasion probability. Ponds connected to invaded locations with intermediate bullfrog abundances showed the highest invasion likelihood, with colonization odds more than twice those associated with connections to ponds with low bullfrog abundances, whereas connections to ponds with high abundances had more moderate effects. Our results highlighted how ponds with intermediate bullfrog abundance play a crucial role in facilitating the invasion spread, this is most likely due to higher propagule release. Ponds with high bullfrog abundance were likely constrained by density-dependent effects, reducing the survival and dispersal of metamorphs. Our study highlights that prioritizing bullfrog eradication in systems with intermediate abundances may be more effective to prevent the expansion of the invasion. We note that landscape features and population demography within invaded areas could be more interrelated than commonly assumed and should be jointly considered in invasive species management strategies.