How could introduced species disrupt existing feeding relationships

It could mean that the new species eats the same food that the original species eats meaning that both populations would be forced to shrink. it could also mean that if the introduced animal eats one of the current inhabitants then the current predator of that species would deplete and the new species would thrive on the new food source. the food that the old species ate would also thrive without its predator.

It may wipe it out by eating the food the native species eats