Abstract
Large carnivores living in tropical rainforests are under immense pressure from the rapid conversion of their habitat. In response, millions of dollars are spent on conserving these species. However, the cost-effectiveness of such investments is poorly understood and this is largely because the requisite population estimates are difficult to achieve at appropriate spatial scales for these secretive species. Here, we apply a robust detection/non-detection sampling technique to produce the first reliable population metric (occupancy) for a critically endangered large carnivore; the Sumatran tiger (Panthera tigris sumatrae). From 2007–2009, seven landscapes were surveyed through 13,511 km of transects in 394 grid cells (17×17 km). Tiger sign was detected in 206 cells, producing a naive estimate of 0.52. However, after controlling for an unequal detection probability (where p = 0.13±0.017; ±S.E.), the estimated tiger occupancy was 0.72±0.048. Whilst the Sumatra-wide survey results gives cause for optimism, a significant negative correlation between occupancy and recent deforestation was found. For example, the Northern Riau landscape had an average deforestation rate of 9.8%/yr and by far the lowest occupancy (0.33±0.055). Our results highlight the key tiger areas in need of protection and have led to one area (Leuser-Ulu Masen) being upgraded as a ‘global priority’ for wild tiger conservation. However, Sumatra has one of the highest global deforestation rates and the two largest tiger landscapes identified in this study will become highly fragmented if their respective proposed roads networks are approved. Thus, it is vital that the Indonesian government tackles these threats, e.g. through improved land-use planning, if it is to succeed in meeting its ambitious National Tiger Recovery Plan targets of doubling the number of Sumatran tigers by 2022.
Highlights
Setting conservation priorities for top predators requires repeatable and robust estimates of abundance or distribution over large areas
Cell size was based on the putative home range size of an adult male Sumatran tiger to allow changes in the distribution of resident tigers to be reflected as changes in the proportion of the grid cells occupied
Managers require population estimates that cover meaningful units, whether at landscape, sub-species or species scales. Gaining such information for cryptic species living at low densities across large areas has previously proved difficult
Summary
Setting conservation priorities for top predators requires repeatable and robust estimates of abundance or distribution over large areas. For conservation managers working in tropical rainforests, obtaining such estimates for these taxa are difficult because they tend to be cryptic and live at low densities across large areas [2,3]. This situation is pertinent to Sumatran rainforests that support several iconic and highly threatened wildlife species, such as the tiger. Extensive tracts of lower elevation forests were excised during their designation to allow for commercial logging These lowland forests can support relatively high densities of Sumatran tigers and act as important corridors that maintain landscape integrity and population viability [4]. Conservation investment has tended to overlook unprotected lowland forests across Sumatra and, as a result, these highly accessible rainforest habitats (,150 m) have come under immense pressure and are experiencing disproportionately high rates of deforestation (3.3%/yr; [5])
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