We chose to study eight small herds of caribou located in Eastern British Columbia and Western Alberta (Figure 1). These herds are part of the central mountain population of caribou. These herds were chosen because both direct and indirect predation pressures are important threats for this population (COSEWIC, 2014).
Figure 1. A map showing the location of the eight study herds raging throughout the mountains in Eastern British Columbia and Western Alberta.
This study took place over a three month period in the spring. Firstly, a number of male and female adult individuals of each heard were tagged and weighed at the beginning of the season. Total number of calves was also recorded. We then applied the different management techniques to the herds. Two herds received predator control and supplemental feeding, two herds received only predator control, two herds received supplemental feeding, and two herds were left unmanaged as a control. We chose to use two herds for each treatment in order to have at least one replication of each management method. For the herds that received supplemental feeding, 50kg of nutritional pellets were supplied for each herd every day. These pellets were highly dense in nutrients and were made from a combination of wheat and barley. In the herds that were subject to predator control, wolf culls were implemented for nearby packs throughout the duration of the study. It is estimated that in these areas wolf populations were reduced by 60-80%. At the end of the season, the tagged individuals were weighed once more, and the number of calf births and deaths were recorded.
Statistical Analysis
We completed a two-factor analysis of variance with effect size statistics to compare the effect of predator control and supplemental feeding on population growth. This was chosen because it allows us to test multiple treatments (predator control and supplemental feeding). This statistical analysis allowed us to test if there was an interaction between our predictor variables, and if either variable had an effect on population growth. The effect size statistics allowed us to effectively determine the population gains we could expect for predetermined levels of certainty, for the different treatments.