Uprooting the Food Web

Another problem attributed to invasive species is that of upsetting the food web of an ecosystem. When a new animal is added to an system, it needs to have something to eat and it needs a place on a trophic level. This can cause a large reshuffling in which population sizes can change, or possibly become extinct.

One classic example of an invasive species which caused problems is the Cane Toad (Bufo marinus) in Australia. The Cane Toad is a species of amphibian native to Central and South America. It was introduced several years ago in Australia as a way to eradicate Cane Grubs, which were small insects eating the roots of sugar cane being grown in Australia. But rather than getting rid of the bug infection, the Cane Toad ate anything else, and has now spread over about one-fourth of the country. This wide distribution is due to the fact that the toad is incredibly poisonous and it has nothing that can eat it where it is located. Several high-level predators have been found dead with dead Cane Toads in their mouths. So without a population control, their numbers exploded, and with more toads, Australia began to see a decline in the populations of animals that the toads were eating. This one species rearranged the whole ecosystem simply because nothing can eat them.

Another species that is slowly becoming invasive is the Lionfish (Pterois volitans), off the eastern coast of the United States and in warmer tropical waters. Like the Cane Toad, Lionfish are poisonous, so they do not possess any natural predators in the ecosystems they invade. It also preys upon native species in the Atlantic ocean, upsetting the natural sizes of populations. They mainly cause the same problems the Cane Toads cause in Australia, increasing in numbers with the only limiting factor being the amount of food available to them.

In the article on the Mediterranean sea, they examine a type of algae that has for the most part pushed all life to the fringes of their sprawling meadows. They spread rapidly and, as if sheer numbers was not enough, they secrete toxins that kill mollusks, fish, and sea urchins. They effectively take over a large area of water and once they spread, it becomes very difficult to get rid of it.

In short, invasive species can rearrange the food web of an entire ecosystem and alter it completely. Isn't that enough to deem it a problem?