Abstract Biological invasions drive biodiversity loss and ecosystem degradation, highlighting the need to better understand the mechanisms underlying their spread. This is particularly relevant during early invasion stages, when populations transition from local establishments to regional advancing fronts. Although interactions among local demographic processes and landscape‐scale dispersal have been repeatedly proposed as key drivers of invasion expansion, integrated empirical evidence remains scarce. We analysed the early invasion dynamics of the American bullfrog ( Aquarana catesbeiana ), a globally invasive aquatic anuran, across a pondscape in the Pampas grasslands of Uruguay. Using an 11‐year monitoring programme (2012–2022), which captured the onset and early expansion of the invasion, we assessed how landscape connectivity, source population abundance and environmental variables influenced the initial spatial expansion of the invasion process using the graph theory approach. The number of invaded ponds increased at an annual rate of 7.7% over the study period. A binomial model of invasion probability showed that connectivity to previously invaded ponds interacted with bullfrog abundance to determine invasion probability. Ponds connected to invaded sites with intermediate bullfrog abundances exhibited the highest invasion likelihood, with colonization odds more than twice those associated with connections to low‐abundance sites, whereas connections to high‐abundance sites had more moderate effects. These results indicate that intermediate‐abundance populations maximize invasion spread by generating higher propagule pressure, whereas high‐abundance populations may experience density‐dependent constraints that limit dispersal and recruitment. Synthesis and applications . Our results show that invasion risk emerges from the interaction between landscape connectivity and local population demography. For invasive species with complex life cycles—particularly those exhibiting cannibalistic behaviour—management actions should prioritize populations with intermediate abundances that act as key sources of spread, rather than focusing exclusively on high‐density populations. Integrating population‐level processes with spatial connectivity offers a broadly applicable framework for identifying priority sites, optimizing resource allocation and improving the effectiveness of invasive species management across pond networks and other spatially structured landscapes.
Gobel et al. (Sun,) studied this question.