•what's the minimum number of days you should exercise to improve cardiovascular fitness

 To improve overall cardiovascular health, we suggest at least 150 mins per week of moderate exercise or 75 minutes per week of vigorous exercise (or a combination of moderate and vigorous activity.) Thirty minutes a day, five times a week is a easy goal to remember. 

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