Refer to the Figure

Refer to the figure.
The figure shows results of Steadman's study of bird species on the Pacific Islands. According to this figure, the study demonstrated that

A) humans have had an impact on ecosystems for thousands of years.
B) Earth's biota is becoming increasingly homogenized.
C) extinctions eliminate individual species but have little effect on ecological communities.
D) it is difficult to determine when a species becomes extinct.