Fertility is the measure of the ability to become . What one word completes the sentence

Would really appreciate it, i have an idea but not completely sure

What term describes a doctor who becomes a specialist by meeting standards beyond those of getting a license and passing a test in the specialty area?

Which of the following is an example of competition a. the leaves of a tree prevent a small shrub from getting sunlight. three species of birds feed a different heights in the same tree. b. three species of birds feed at different heights in the same tree c. zebra and giraffe’s feed on different grassland plants d. cats living in two different homes eat the same brand of cat food.