Thinking Questions

1. In the 1940's, two brothers – Adolph and Olaus Murie – studied the Dall's Sheep (among many other mammals) in what is now Denali Nat'l Park in central Alaska. By estimating the age at death from the size of horns they found as they hiked throughout the park, the Murie brothers constructed the life table we used in Discussion (see Problem Set #4)

(a) This is a static life table – What assumptions are associated with this type of life table?

(b) An important ecological question in the 1940’s was, "What is the typical life expectancy of a Dall's sheep in Denali?" Life expectancy is often expressed as the youngest age at which at least 50% of the individuals die. Using the life table data above, what was Adolph and Olaus Murie's answer?

(c) Mardy (Buecher) Murie was one of the most eloquent and influential proponents of Alaskan wilderness preservation. An important conservation question she was interested in at the time was, "Are most Dall's Sheep dying as a result of hunting, or are they dying of 'natural causes'?" Most hunters prefer to shoot sheep when they are most healthy (providing the best meat and most impressive horns) – this is typically between the ages of 6 and 9 years. In contrast, most natural mortality occurs either when the lambs are either (a) very young (i.e., 0-1 years) when they occasionally fall to their deaths from high rock cliffs by slipping or being pushed off by attacking golden eagles, or (b) when the sheep are very old (11-15 years) and unable to find sufficient forage to survive the long bitter Alaskan winter. Using the life table data above, what might Mardy Murie conclude about the severity of hunting Dall's Sheep in Denali? How would you expect the life table to change if hunting were discontinued in the park?