The introduction of some nonnative species has been helpful. How can initially useful organisms become harmful to an ecosystem?

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Explanation:

The introduction of nonnative species in an ecosystem maybe both helpful and harmful. Initially, the introduced nonnative species maybe prove helpful in some ways.

As time goes on, the nonnative species begin to compete with the native species for resources in the ecosystem. The nonnative species may outdo the native species in such competition and entirely replace them. This may ultimately lead to a permanent loss of the native species from the ecosystem.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.