What is the name
of the reigning
theory about the
origins of the
universe?

Sorry i dont understand the question can you rephase it?

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.