It is the isthmus of Suez which is very narrow.
Answer:
The biosphere is made up of the parts of Earth where life exists.
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Below are the choices. the answer is C.
A) mass extinctions, leading to bottleneck effect
B) major evolutionary innovations, leading to rafting to nearby continents
C) a variety of empty ecological niches, leading to adaptive radiation
<span>D) adaptive radiation, leading to founder effect</span>
Mountain chains and river systems generally run North-South throughout the continent thus making for formidable barriers to East-West expansion.
