Investigating the demography and dynamics of a low-density tiger population in Southeast Asia: What limits recovery?

Prey depletion, direct poaching, and habitat fragmentation are driving global declines of carnivore species, but the specific consequences of these impacts on population demography have not been widely studied, obscuring an understanding of why some populations recover while others flounder. This 11-year study sought to uncover what constrains recovery of a low-density tiger population in Thailand, by investigating population dynamics with respect to three key mechanisms potentially affecting vital rates: tiger poaching, prey depletion, and immigration. Our site resembled most Southeast Asian tiger populations in that tiger and prey abundance were both low, but it was unusual in sharing landscape connectivity with the largest tiger population remaining in Southeast Asia. We identified tigers with camera traps and applied a Pradel robust design model to estimate survival, recruitment, immigration, and population growth rate. We obtained information on cub production through observations of dependent young with their mother. The small population (7-11 adults) was stable over time but did not increase ( $\lambda$ = 1.006). This inertia corresponded with the status of key prey species, which occurred at low density and had flat population trends. Female survival rate was high (0.823), but reproduction rate (0.514) and cub survival (0.313) were 2-3 times lower than other tiger populations in Asia where prey availability is higher. This pattern of flat population trend, high adult survival, and low reproduction is indicative of the effects of prey scarcity, rather than direct poaching, as the essential constraint on recovery. Most recruitment of new tigers came from immigration, with 67% of the resident females being born outside, rather than locally. High female survival plus immigration were critical to sustaining this population, and represent an essential foundation for future recovery, but this potential is impeded by prey scarcity which suppresses reproductive success. Managers can unblock the path to recovery by increasing abundance and distribution of preferred prey. This would allow resident females to reproduce more consistently and boost survival rates of their cubs, while creating new high-quality habitats for additional females to settle in, whether they are locally born or arrive through immigration.