If a new specie is introduced into the ecosystem which is already in balance condition, the whole ecosystem is disturbed. It is because that the new specie feed on the organisms present in that particular environment and decrease occurs in the food availability for other species. It also decreases the population or sometime full extinction of that specie.
The invasive species would disrupt the balanced environment because the only way the islands environment is balanced is because it has the same constant species reproducing and living there. I’d a new species colonized it would corrupt the whole thing, making it unbalanced and possibly killing off a significant part of the food chain.
