Tiger Population Simulation Model: Practical Conservation Applications Analyzing the effects of Poaching, Inbreeding Depression and Habitat Connectivity on Tiger Population Viability

The number of wild tigers is declining rapidly throughout the world. The vast majority of remaining wild tiger populations persists in small isolated fragments of suitable habitat distributed across the tiger's former range. Remaining small populations are under threat from extrinsic factors such as poaching and habitat loss and from intrinsic factors such as demographic, genetic and environmental stochasticity. To evaluate the viability of remaining wild tiger populations and to examine the implications of implementing various management strategies, I developed a tiger population simulation model that is specific for tigers and is based on the extensive data set collected at Chitwan National Park in Nepal since the early 1970s. With this model, I explored the effect of poaching on the long-term viability of remaining tiger populations (Chapter 3) and the interaction of inbreeding depression and genetic exchange on tiger population persistence (Chapter 4). Poaching tigers primarily for their bones for use in traditional Chinese medicine has become the latest threat to the persistence of wild tiger populations throughout the world. I simulated three representative population sizes of tigers with various rates and durations of poaching and found that as poaching continues over time, the probability of population extinction increased sigmoidally; a critical zone existed where a small incremental increase in poaching greatly increased the probability of extinction. The implication is that poaching may not at first be seen as a threat, but could suddenly become one. Moreover, even if poaching is effectively stopped, tiger populations will still be vulnerable and could go extinct due to demographic and environmental stochasticity. The model also indicated that poaching reduces genetic variability which could further reduce population viability due to inbreeding depression. The longer that poaching is allowed to continue, the more vulnerable a population will be to these stochastic events. Secondly, I used the model to examine: 1) the probability of extinction of representative sizes of remaining wild tiger populations due to demographic stochasticity and inbreeding depression; 2) the degree to which dispersal among populations will reduce inbreeding depression; 3) the impact of delayed genetic exchange among populations on population viability; and 4) the implications of management actions to reduce inbreeding depression. The simulations indicated that many of the smaller remaining populations are at a very high level of risk, with all populations going extinct within the next 50 years due to inbreeding depression and demographic stochasticity. Remaining larger populations are at a lower risk, with genetic exchange significantly lowering extinction risk. Similar to the poaching results, a population extinction threshold appears to exist at a particular point in time. The location and slope of the threshold is a function of population size, level of genetic exchange and genetic load. Genetic load in wild tiger population is not clearly understood and therefore deserves immediate research attention. Generally, these results illustrate the need to focus conservation efforts to maintain the size of existing larger tiger populations, to enhance habitat where possible in order to increase tiger numbers for populations occurring in large blocks of degraded habitat, and to provide for genetic exchange among fragmented populations.