In accordance with Wilson and MacArthur's theory of island biogeography, the following equations represent the immigration and extinction rates of species of beetles on a small island. (I = immigration rate of species per month; E = extinction rate of species per month; S = number of species currently on the island.)
I = 9 ? 0.2S
E = 0.3S
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If there are 25 species on the island, the expected immigration rate is _______ species per month and the expected extinction rate is _______ species per month.
A) 1; 7.5
B) 4; 7.5
C) 7.5; 1
D) 7.5; 4