Potassium, 4 shells, 1 valence electron
Because these non native species can cause competition for the same food source as the native species thus making it harder for the native species to survive. Also the non native species could see the native species as food causing them to die out. As well as introducing new diseases that these native species don’t know how to defend themselves from
There are only so many resources that can be used and if all of them are used they don't have enough materials or food.
