Reconstructing ancient ecosystems: guanaco and marine carrion as drivers of predator-prey networks in Southern South America

Understanding ancient trophic dynamics and human integration in terrestrial high-latitude ecosystems requires moving beyond traditional taxonomic lists to evaluate structural biological interactions. This study presents the first probabilistic, trait-based bipartite network reconstruction of ancient predator-prey assemblages in northern Tierra del Fuego, Southern South America, based on archeological records. By integrating a comprehensive zooarcheological dataset spanning 50 spatial-temporal contexts from the late Pleistocene through the late Holocene across steppe and forest habitats, we model trophic interactions including human subsistence strategies. In this region, dominated by grassy steppes and the forest-steppe ecotone, terrestrial hunter-gatherer societies were embedded in a complex predator-prey network in which the guanaco ( Lama guanicoe ) played a central role. However, the trophic structure of these interactions and how the introduction of humans as an unprecedented predator affected community-level properties is poorly understood. Our results reveal a significant chronological transformation in network architecture and diet composition. During the late Pleistocene, communities exhibited lower interaction diversity and high specialization centered around megaherbivores and multiple large predators. Following megafaunal extinction and island isolation during the mid-Holocene, the guanaco emerged as an enduring keystone herbivore and dietary anchor, while marine-derived carrion and littoral resources (mollusks and pinnipeds) provided critical energy subsidies. Humans acted as highly plastic generalist consumers, influencing network architecture across diverse habitats. In the steppe, foragers employed broad-spectrum strategies, whereas forest assemblages reflected specialized reliance on coastal resources. Ultimately, this community-level framework demonstrates that despite intense environmental shifts and insularization, the guanaco and marine necromass served as foundational trophic stabilizers, maintaining ecosystem and subsistence resilience over millennia.