Colonization of Amazonia by non-indigenous populations over the past 500 years led to catastrophic demographic collapses of indigenous populations 1–3. The irreversible threats from large-scale habitat loss via deforestation and conversion of land to agriculture and pasture potentially paint a bleak future for indigenous populations 4,5, and these threats have intensified under recent political regimes who sought to undermine legal authority to reduce deforestation 6 Despite the incessant external pressures from the outside world, some remote protected areas in the upper Amazon watershed support remnant indigenous societies referred to as uncontacted or isolated populations 7,8. There are estimated to be between 30–50 isolated indigenous societies remaining in Amazonia, but most of their populations are likely small and fragmented 9,10. Governments and the United Nations espouse no-contact policies for these isolated indigenous populations with the belief that they are safest if left to themselves 11. If this “leave-them-alone” policy is successful, populations should demonstrate long-term population viability and growth. The long-term viability of such a strategy is arguably doubtful, given a history of illegal incursions by resource-extraction outfits and the ever-present potential for disease epidemics 12. Yet another line of argument is that the history of disease, displacement, violence, and exploitation by outgroups after contact means that isolation and legal protections are the only means to ensure long term survival for these groups 13. Where protection of isolation is favored, there are numerous strategies to protect isolated communities 14. Either way, understanding the population dynamics and growth of these uncontacted groups, as well as the risk of encroachment and incursion by resource extraction, is vital for their long-term viability alongside further legal protection.
Unfortunately, despite being isolated from the outside world, these indigenous societies face uncertain prospects for long-term survival from pressures far beyond their control 14. News about isolated indigenous societies is mostly tragic, from violent encounters with outsiders to illegal exploitation of their land and resources to cultural and linguistic extinction, as in the recent death of “Tanaru” 15. The COVID-19 pandemic elevated the risk for indigenous groups who experienced outbreaks and elevated excess death rates 16–18. The pandemic has also resulted in elevated resource conflicts for indigenous Amazonian communities, including areas of mining and resource theft 19. Increased resource extraction in the Amazon is a salient threat to isolated indigenous groups as 97% of mining requests to the National Mining Agency in Brazil are in indigenous lands with isolated groups 20,21. That some isolated societies have survived and maintained traditional lifeways is remarkable given that powerful external forces from logging, mining, poaching, narcotrafficking, and disease pose direct threats to their existence 20–25.
Evidence that some isolated populations may be growing and thriving would offer renewed hope for their long-term survival and provide some support for no-contact policies. Direct investigation into isolated indigenous population dynamics is challenging both ethically and logistically. For example, it is not possible to collect census data, and overflights are unreliable for population estimates as people often actively avoid detection or are unobservable under living structures or the rainforest canopy. Hence remote monitoring is a useful method with which to study isolated indigenous demography and spatial ecology 26,27. In contrast to overflights, remote sensing is safe and noninvasive. However, remote sensing approaches necessarily rely on indirect proxies of population size, such as the total cleared area of villages and gardens, the number of fire detections from burning associated with forest clearing, the number and size of living structures, and the occurrence or not of village fissioning 9. Also crucially important is the need to remotely assess the spatial resource needs of indigenous societies in a region heavily impacted by deforestation and other threats. For example, the use of geospatial data to trace the effects of oil spills in the Ecuadorian Amazon highlights how oil spills impact hydraulic systems and threaten indigenous communities, including uncontacted groups 28. Remote sensing can therefore be part of a larger geospatial toolkit to safely and remotely assess the outside threats to the health and livelihoods of isolated indigenous groups.
An important aspect of the long-term viability of populations is population substructure. In metapopulation ecology, a crucial component to of demographic resilience is the “rescue effect” where spatially-discrete reproductive subpopulations are linked through migration 29 The vulnerability of local subpopulations to localized catastrophic events, disease outbreaks, or environmental and demographic fluctuations is mitigated through reproductive links with other subpopulations subject to their own set of vulnerabilities within the larger metapopulation. As a result, metapopulations, or reproductive connections amongst subpopulations, are known to contribute to population viability 30,31 as they display increased resilience over single populations by displacing localized risk. This metapopulation structure is likely important for isolated human groups in Amazonia. Local isolated groups are undoubtedly subject to many local vulnerabilities, enhanced by the catastrophic demographic collapse of larger-scale metapopulations over the last few centuries. Remnant, isolated populations are vulnerable to both demographic and environmental stochasticity due to their small sizes and the added risk that they are also likely no longer embedded within fully functioning metapopulations.
Given the numerous threats to health and livelihoods of indigenous communities via encroachment, disease, and resource extraction, as well as intrinsic threats of population decline and collapse, remote assessments of isolated groups can provide information to influence policy on environment protections as well as the ongoing debate over isolationism versus controlled contact. We join the chorus of others calling for additional study, including safe and remote monitoring of isolated indigenous communities, to better understand the vulnerabilities and threats these communities face 14,20,21. Information yielded from these studies is necessary to safeguard the future of isolated indigenous communities. The violent and deadly history of past contact events implies that collection of remote data is the only possibility to understand the threats to health and wellbeing of these groups. Here we explore the use of remote sensing methods to examine longitudinal change in land use of two isolated Amazonian groups (Fig. 1) to help assess population health and long-term viability.