As invasive species, how does the introduction of the feral pig and the water hyacinth impact an ecosystem?

They control the growth of native species, including those they consume, as well as those that consume them. This is just a hypothesis of mine, but is somewhat justified by the term "invasive" ...

Found in many parts of the world, the feral pig damages crops by trampling and "rooting." It attacks and feeds on livestock (mainly lambs) and causes the spread of weeds. It also spreads diseases such as leptospirosis and foot-and-mouth disease. Feral pigs feed primarily on plants but also on earthworms, insects, amphibians, reptiles, and birds. The water hyacinth spreads at extremely fast rates, in favorable conditions doubling its numbers in as little as 12 days. The plant, which floats on the water's surface, can cover large areas, thus limiting boat traffic, swimming, and fishing. By blanketing the surface, the plant also prevents sunlight from entering the water. Moreover, when it dies, the decaying plant matter robs the water of oxygen. The reduced amount of sunlight and oxygen in the water disrupts plant and animal life, adversely affecting the habitat's biodiversity.