Reindeer Island: A look at Population increases and limiting factors
St. Paul Island is one of the Pribilof Islands in the Bering Sea near Alaska. It is approximately 106 km2 or 41 square miles in size and is more than 200 miles from the mainland. James Judge and Dr. Warren Evermann of the Bureau of Fisheries, with the cooperation of the Bureau of Education and the Revenue Cutter Service, introduced twenty-five reindeer (Rangifer tarandus) on St. Paul Island in 1911. By 1921, there were 250 reindeer on St. Paul Island, and by 1938, there were about 2,000 reindeer on St. Paul Island. Poaching, harsh winter weather and starvation due to overgrazing of the tundra caused the St. Paul herd to become severely depleted in the 1940s. In 1950, only eight reindeer remained at St. Paul Island.. In 2007, several hundred reindeer roam St. Paul Island. The reindeer are hunted by permit. The U.S. Department of Agriculture, Natural Resource Conservation Service, with federal, state, and local assistance, has developed a plan for reindeer management on St. Paul Island (USDA undated, ca. 2001).
Questions: With your team or by yourself (which ever your teacher determined) study the graph and information from above and answer the questions below.
1. What was the size of the reindeer population at the beginning of the study, 1911?
2. What was the size of the reindeer herd in 1920?
3. What was the difference in the number of reindeer between 1911-1920?
4. What was the average annual increase in the number of reindeer between 1911-1920? (Hint: how many years past?)
5. What was the difference in population size between the years of 1920-1030?
6. What was the average annual increase in the number of reindeer between 1920 and 1930?
7. What was the average annual increase in the number of reindeer between 1930 and 1938?
8. During which time period was the increase in the reindeer population the greatest; 1911-1920, 1920-1930, or 1930-1938?
9. When did the population of reindeer peek? What was the population at that year?
10. In 1950 only eight reindeer were still alive. What was the average annual decrease in the number of reindeer between 1938 and 1950? (Hint: how many died; in how many years?
Analysis:
1. What might account for the tremendous increase in the population of the reindeer between 1930 and 1938, as compared with the rate of growth during the first two decades, 1911-1920 and 1921-1930?
2. What factor or factors finally limited the growth of the reindeer population? Identify those listed as density-dependent or density-independent limiting factors.
3. What evidence is there that the number of reindeer on the island exceeded the carrying capacity of the island?
4. What does this study suggest about exponential growth of unchecked populations?
5. How might interactions between the reindeer and a predator have affected the growth of the reindeer population? How might interactions between the reindeer and hunters affected the population growth?
Part B: So what about resources?
In general, in order for individuals in a population to sustain themselves, the individuals must have food for energy. The amount of food available to each would depend both on the total amount of food available and on the total population at that time. If we know both of these things, then we can calculate the amount of food available per individual in the different populations.
1. Make a copy of the table into your journal and complete it by calculating the number of units of food available to each individual. NOTE: the total amount of food available is always 100 units. The first calculation has been done for you based on a population size of 2. For the population size of 2, the amount of food available per individual is 50 units (100 units/2 individuals).
2. Use the data table to create a graph of the relationship between the size of the population (x-axis) and the number of units of food available per individual (y-axis).
Population / Population size / Food allocation/ individualA / 2 / 50
B / 4 / ?
C / 8 / ?
D / 16 / ?
E / 32 / ?
F / 64 / ?
G / 128 / ?
Final questions:
Use the data table you completed and your graph to help answer the following question.
1. How does the amount of food available to each individual change as the population size increases? Be specific…don’t just say it increases or decreases.
2. Imagine that in order to survive individuals need a minimum daily requirement of 3.0 units of food. How would this minimum requirement affect the survival rates of individuals in population G? What about populations F & G?
3. Using the information from question 2, what is the approximate carrying capacity of the population?
Current Events:
June 5, 2012:
Stephanie Joyce, of KUCB in Unalaska, reports a dwindling population of free-range reindeer on St. Paul Island, Alaska, has locals on edge for the upcoming hunting season.
After a brutal winter on the island, the population has dropped dramatically. The pre-winter count of 500 animals is now estimated to be around 125. Islanders rely on a healthy reindeer population to supplement their diets.
The history of St. Paul, a remote island located in the Bering Sea, is a difficult one. The Privylovs, which including St. Paul, St. Peter and St. George, were uninhabited islands discovered in 1786 by Russian fur trader Gavrili Pribylov. In 1788 the Russian-American Company enslaved and relocated the native population of Atka and Unalaska to the Pribilofs. The only sources of food on the islands were seals, seabirds and some vegetation, so in the early 1900s reindeer were introduced. Reindeer remain a vital food source to the 479 residents, most of whom live a subsistence existence. Groceries, particularly other meats, are extremely expensive. Ground beef, for example, cost $7 a pound on St. Paul.
According to Joyce, The St. Paul Tribal Government, which has managed the herd since the 1980s, will attempt another count later in the summer. But it is not expected the numbers will be much higher.