In a wave of global conservationism, Ecuador established two large protected areas in its Amazon region in 1979. One of these is the Reserva de Producción Faunística Cuyabeno (RPFC), located in the northeastern corner of the country. Given that this land was previously managed as commons by local indigenous groups, the establishment of protected areas has had numerous consequences for these people. The research conducted comprised three months’ fieldwork in three of the affected Siona communities, primarily through the use of participant observation. Based on the framework developed by Ensminger, this paper demonstrates how institutional change has occurred in the last few centuries with the arrival of various frontiers overriding the region. This has led to the almost total eradication of traditional institutions and the introduction of a new ideology, namely conservationism. In order to legitimize their existence in the Reserve, indigenous groups are compelled to argue in a conservationist discourse if they want to stay in their ancestral territory. The article discusses tourism as one key impact on the lives of the local Siona, alongside their response to the grabbing process, which takes the form of a re-creation of their identity, including institution shopping from below. This article contributes to the debate on commons grabbing from the perspective of local actors by arguing that institution shopping from below does not necessarily mean a loss of authenticity, considering different ontological perspectives in the process of identity construction.