Population ecology provides a general framework for guiding restoration of endangered species and for predicting how their populations will respond during restoration. Gray wolf restoration provides a clear example of the utility of population ecology for managing endangered species.

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Genetic analysis gives environmental scientists essential tools for restoring endangered species populations. For instance, restoration of wolf populations in Yellowstone, Idaho, and along the Arizona–New Mexico border would require that founding populations have diverse genetics. That’s why, following the initial introduction of wolves into Yellowstone in 1995, an additional 17 Canadian wolves were brought in the subsequent year.

Compared with the wolves of the Northern Rocky Mountains, there is much less genetic variation among the small population of surviving Mexican gray wolves (see Figure 3.24, page 80), which are the descendants of three unrelated but highly inbred lineages. However, biologists discovered sufficient remaining diversity in these three surviving lineages to improve the chances of success by the population. By crossbreeding descendants of the three lineages, they have been able to more than double litter sizes from an average of 3.5 or 3.6 pups to 7.5 pups per litter (Figure 3.29). In addition, crossbred Mexican wolf pups also have an 18% to 21% higher chance of surviving to 6 months of age. Such positive effects of increasing genetic diversity are called genetic rescue.

The wolf population of the Northern Rocky Mountains Recovery Area grew quickly following their reintroduction to Yellowstone and Idaho. Conservation biologists set a restoration goal of 30 breeding pairs, defined as a male and female that successfully rear at least two pups which survive to the end of the calendar year. That goal was met in 2000 and was quickly exceeded (Figure 3.30a). By 2007 there were over 100 breeding pairs across the Northern Rocky Mountain Recovery Area, which includes parts of Idaho, Montana, and Wyoming, and the number of breeding pairs appeared to be stabilizing, a pattern suggesting S-shaped, or logistic, population growth (see Figure 3.11, page 69). Since generally only the dominant male and female in a wolf pack breed, the total number of wolves in the recovery area is far higher than the number of breeding pairs.

In fact, the population grew to over 1,700 wolves by 2011 (Figure 3.30b), then dropped slightly to 1,600 individuals in 2013. Looking at just one part of the range, the Yellowstone wolf population peaked in 2003 at 172, then declined to fewer than 100 by 2009, where their numbers have approximately stabilized since. Again, the growth of the restored wolf population appears to be following an S-shaped pattern at both regional and local scales, as we would expect from a highly territorial, K-selected species like the gray wolf.

Wolves remain a charged subject in Rocky Mountain states, where ranchers—and their supporters in state government—oppose their preservation. As a consequence of their dramatic recovery and pressure from state officials and interest groups, the U.S. Fish and Wildlife Service classified the gray wolf population of the Northern Rocky Mountain states as recovered and took them off the U.S. endangered species list in 2012. With delisting, responsibility for management of gray wolf populations was returned to the states of Idaho, Montana, and Wyoming, opening a controversial hunting season on the wolves. In September 2014, however, the Federal District Court for the District of Columbia restored wolves in Wyoming to endangered species status.