What is the most efficient way to extract oxygen from the environment?
a. countercurrent
b. crosscurrent
c. uniform pool

1. in what ways have non-native species been beneficial? 2. what are some of the hypotheses for the collapse of honeybee colonies? 3. distinguish between regional and functional extinction. 4. why is it difficult to measure background extinction rates? 5. what three factors are most important in causing extinction rates to climb?