US Geological Survey
Date of this Version
2015
Citation
Integrative Zoology, doi: 10.1111/1749-4877. 12141
Abstract
The world’s tiger (Panthera tigris, Linnaeus 1758) range countries agreed to double tiger numbers over twelve years, but whether such an increase is biologically feasible has not been assessed. Long-term monitoring of tigers in Sikhote-Alin Biosphere Zapovednik (SABZ), Russia provided an opportunity to determine growth rates of a recovering population. A 41-year growth phase was followed by a rapid decline in tiger numbers. Annual growth rates during the growth phase averaged 4.6%, beginning near 10% in the earliest years but quickly dropping below 5%. Sex ratio (females per male) mirrored growth rates, declining as population size increased. The rapid decline from 2008 to 2011 appeared to be tied to multiple factors, including poaching, severe winters, and disease. Reproductive indicators of this population are similar to those of Bengal tiger populations, suggesting that growth rates may be similar. Five conclusions relevant to tiger conservation are: 1) tiger populations likely in general grow slowly – 3-5% yearly increases are realistic and larger growth rates are likely only when populations are highly depressed, mortality rates are low, and prey populations are high relative to numbers of adult females; 2) while more research is needed, it should not be assumed that tiger populations with high prey densities will necessarily grow more quickly than populations with low prey densities; 3) while growth is slow, decline can be rapid; 4) because declines can happen so quickly, there is a constant need to monitor populations and be ready to respond with appropriate and timely conservation interventions if tiger populations are to remain secure; and 5) an average annual growth rate across all tiger populations of 6%, required to reach the Global Tiger Initiative’s goal of doubling tiger numbers in 12 years, is a noble but unlikely scenario.