Lack of hunters and predators are the two factors that affect the population of reindeer between 1930 and 1938.
EXPLANATION:
Initially, around 40 Reindeer's resides in the St.Paul Island in Alaska. The hunting was not allowed and there were means no predators for reindeer. This led to an increase in the number of Reindeer's as the death rate was low and the birth rate was high.
Thus due to this, the population growth of reindeer increases rapidly. Also, it increased the number of Reindeer's to 2000. But there was a decline in the number of Reindeer's at the end of the year 1938.
