Using the "placeholder" concept to reduce genetic introgression of an endangered carnivore
One of the most endangered species is the red wolf, Canis rufus. Reintroduction of the red wolf began in 1987, but in 1993 hybridization between coyotes (Canis latrans) and wolves was documented. To reduce genetic introgression, coyotes and coyote–wolf hybrids were captured, sterilized, and released as “placeholders”. Placeholders held territories until either displaced or killed by a wolf, or management personnel removed them before releasing a wolf. We evaluated the placeholder concept by examining the number of animals sterilized and released, likelihood of displacement by a wolf, factors influencing displacements, territory fidelity of placeholders, and survival rates and causes of mortality of placeholders and wolves. Of the 182 placeholders, 125 were coyotes and 57 were hybrids. From 1999 to 2013, 51 placeholders were displaced or killed by wolves, and 16 were removed by management personnel. Thus, 37% of the placeholders were displaced leading to occupancy by a wolf. Most displacements occurred in winter (43%) and were always by the same sex. Males were more likely to be displaced than females. Home range characteristics influencing the probability of displacement included home-range size (i.e., more placeholders displaced from larger home ranges) and road density (i.e., more placeholders displaced from home ranges with lower road density). Annual survival of placeholders was higher than wolves in 12 of 14 years, with cause-specific mortality similar among wolves and placeholders. Placeholders provided territories for wolves to colonize, yet reduced the production of hybrid litters, thereby limiting genetic introgression to < 4% coyote ancestry in the wolf population.
Gese, Eric M. and Terletzky, Patricia A., "Using the "placeholder" concept to reduce genetic introgression of an endangered carnivore" (2015). Wildland Resources Faculty Publications. Paper 2118.