Question

1a. As part of a conservation team in the Pacific Northwest, we are tasked with studying population demographics of orca whales. Years of observations of orcas in the Juan de Fuca Strait show that the average female orca produces eight calves over the course of her life time. If we assume an even, 1:1 sex ratio between male:female calves, how many great-grandchildren will one female orca reproduce if all calves survive and reproduce? 1b. Observations of a different population of orcas, pelagic pods that inhabit the open ocean, show different demographic parameters. In these studies, females appear to produce an average of two offspring over their lifetimes. Assuming the same sex ratio as above, how many great-grandchildren will a single female orca in this population produce? 1c. Decades of data suggests that the population sizes of both the Juan de Fuca whales and the pelagic whales are stable (not significantly increasing or decreasing). What does this tell us about potential differences in the rates of survival to reproduction between these two populations?

Answer 1

Answer:

1)a):

• female orca whale produces about 8 calves in her lifetime.
• The male and female calves are in the ratio 1:1.

$\rightarrow$We need to determine the number of great grandchildren one female orca can reproduce if all calves survive and reproduce.

Solution:

• A single female will produce 8 progeny, out of which 4 will be female and 4 will be male (1:1 ratio) .
• In next generation, each of the 4 females will reproduce 8 progeny each, 4×8, or 32 progenies. There will be 16 females and 16 males. [ This is the grandchild generation]
• In the next generation, each of 16 females will reproduce 8 progenies each, for a total of 128 great grandchildren (64 females and 64 males).

$\rightarrow$Thus, one female orca will reproduce 128 great grandchildren if all calves survive and reproduce.

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