Scientific explanation for the direct relationship between diversity and stability of an ecosystem could be as follows: Imagine a forest area, where diverse species of plants are growing. Plants harbour a variety of insects on which a lot of bird species would depend for their food.
If a specific plant species dies, the related insect population will be affected that would lead to food unavailability for the birds.
In addition, if the plant species was a nitrogen fixer, the death of these plants would mean no replenishment of soil with nitrogen. This will obviously affect the other ants as well. So, if the cycle continues, the whole abitateco system will be negatively affected.