第一句修改如下:
In other words,the less diverse it is,the less stability the ecosystem has,because the productivity can be seen as an indicator of the ecosystem's health and balance.
第二句没看懂,试着帮你改为如下：
The extinction of hummingbirds will cause the domino effect,which means the birds' extinction will make other species more vulnerable to extinction as a result of the food chain disruption.
其实你英语基础还不错,就是逻辑关系上还要进一步理顺,不要急着堆砌文字,还要避免不必要的重复.