The reintroduction of the gray wolf (Canis lupus) in Yellowstone National Park is one of the most successful examples among carnivores and provides a rare opportunity to study the population dynamics of a long-lived top-predator. The last pack of wolves in YNP disappeared in the mid-1930s after decades of private- and government-led hunting and trapping but were reintroduced in 1995-96 with the goal to restore natural conditions in the park. A total of 31 wolves (14 in January 1995; 17 in January 1996) were translocated from Canada to YNP, radio collared and released in 7 packs.
In a population biology class, I was a part of a team that studied the population growth rate of the gray wolf population that was reintroduced to Yellowstone National Park. In our study, we took advantage of the large amount of data collected on the Yellowstone wolf population after the reintroduction to assess which factors are more likely to influence the success of future wolf reintroductions. At the population level, we the rate of growth and tested for the presence of temporal trend. We also assessed which vital rates affected the population growth the most. At the pack level, we tested the relative importance of factors that affect annual pack growth, focusing specifically on the effect of pack composition, home range size, location with respect to the park boundaries, and habitat composition. Understanding the complex dynamics that control population growth is critical to implementing management practices that benefit wolf populations.
I used data regarding pack home ranges for the years 1995 to 2015 that were supplied by the Yellowstone National Park Wolf Management Office and calculated the percent of each land cover class contained within each pack’s territory in the years 2001, 2006, and 2011 using ArcGIS. For each of the 221 home ranges in the years 1995 to 2014, I calculated home range size in square kilometers and distance from the pack centroids to the Yellowstone Park boundary. Data for habitat analysis were obtained from the Multi-Resolution Land Characteristics Consortium’s National Land Cover Database which provides nation-wide land cover classification at a 30-meter spatial resolution for the years 1992, 2001, 2006, and 2011.
Our results showed that maximizing the survival probability of breeders is one of the key actions to increase the chance of success in establishing of a new reintroduced population and assure a high rate of population growth. Additionally, as smaller packs showed the highest rate of increase in the following year, we determined annual pack growth rate was strongly influenced by the pack size. In YNP, the maximum growth rate (λt=1.69) occurred in the first year following reintroduction; after establishment of the population, the rate dropped and fluctuated around 1.00 (+/- 0.18), ranging between 0.69 and 1.26 in 2000-2013. Lower values corresponded to years in which the populations were affected by disease outbreaks (e.g., canine distemper in 2005). The growth rate values in YNP fall within the range of values reported in a study based on long-term data on three different populations of wolves in North America (Mech and Fieberg (2015) in which growth rate ranges between 0.47 and 1.79 (Denali National Park: [0.71;1.49], Superior National Forest: [0.65;1.54], and Isle Royale National Park: [0.47;1.79]). We found that none of the habitat types considered showed statistically significant difference in prevalence between packs with increasing or decreasing growth rates. Preferred habitats of wolves has been a subject of recent debate, and our findings support the theory that habitat composition within pack annual home range does not impact pack growth rate.
The first poster is one that summarizes our entire study and was presented at the 2018 International Wolf Symposium in Minneapolis, MN. The second poster is one I created to specifically focuses on the work I did isolating habitat types within home ranges. Click to enlarge either image.
