Respuesta :
Answer: It became prey to certain organisms in the river.
It lacked adaptations suitable for that particular ecosystem.
Explanation:
An invasive species is the one which when introduced either accidentally or intentionally to a new ecosystem is capable of causing damage to the native species. Invasive species compete with the members of the native species for resources.
In the given situation, the population of the invasive species increased intially but decline later. This occurred due to two reasons.
1. It became prey to certain organisms in the river. : The invasive species could be used as a food by certain predatory species already present in the river.
2. It lacked adaptations suitable for that particular ecosystem.: Being new to the river ecosystem the invasive species could have adapted as adaptation favours the survival of the organism in unfavorable condition. This resulted in decline of the invasive species population.