A Study of Pikas in a Mountainous Region of California

A study of pikas in a mountainous region of California finds 50 discrete population patches.Counts of the number of individuals in each population are done every 5 years.These counts show that all populations are in decline.After 10 years, 7 populations have become extinct, and after 20 years, 21 have become extinct.None of the patches that went extinct at year 10 are populated again at year 20.This scenario illustrates

A) the rescue effect.
B) the benefit of corridors.
C) environmental resistance.
D) a typical metapopulation.
E) a lack of source and sink populations.