Decreased number of alveoli in the lungs leads to respiratory distress because:

Alveoli is the place where gas exchange happens between the air taken from your nose to the bloodstream.

Less number of alveoli = less efficient gas exchange = less oxygen reached to your cells for respiration/energy = more faster you body has to work to give the required amount of oxygen to your cells = more breaths per minute = more distress

If you remove all the lions from the savanna it will lead to a increase of gazelle and a increase of cheetahs becasue of no competition