CR analyses have recently been supplanted by more robust spatial capture–recapture (SCR) approaches. An important source of controversy arises in how to deal with the known biases inherent in non-spatial capture–recapture (CR) methods, which are prone to overestimating densities by as much as 20–60% 5. Still, the use of CT data to compare trends across diverse sites remains controversial despite its potential to illuminate population dynamics far more than any single-site analysis 7, 8, 9. The widespread proliferation of camera-trap (CT) surveys over the last 15 years, which provide an efficient means of monitoring abundance across wide geographic ranges, has partially solved this problem. Obtaining information on rare apex predators is particularly difficult given their large home ranges, low population densities, and often cryptic nature 4, 5, 6. This is often impeded by methodological differences employed by researchers to collect and analyze data 2, 3. Robust assessments of the spatial distribution and population dynamics of threatened species are crucial for designing effective conservation policies 1. Thus, despite increasing densities in smaller parks, we conclude that there are only two robust populations left with >30 breeding females, indicating Sumatran tigers still face a high risk of extinction unless deforestation can be controlled. However, while tiger numbers may have temporarily risen, the total potential island-wide population declined by 16.6% from 2000 to 2012 due to forest loss and degradation and subpopulations are significantly more fragmented. We find that tiger densities were 47% higher in primary versus degraded forests and, unexpectedly, increased 4.9% per yr from 1996 to 2014, likely indicating a recovery from earlier poaching. We develop an approach to standardize older non-spatial CR and newer spatial CR density estimates and examine trends for critically endangered Sumatran tigers ( Panthera tigris sumatrae) using a meta-regression of 17 existing densities and new estimates from our own fieldwork. The continuing development of improved capture–recapture (CR) modeling techniques used to study apex predators has also limited robust temporal and cross-site analyses due to different methods employed.
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