One of the most debated issues regarding biodiversity, nowadays, is that of introduced or invasive species. What is this all about?

Each species, be it plant, animal or microbial, has its own habitat and, through various trophic and non-trophic relations, it is part of an ecosystem. When it reaches a different ecosystem, it can adapt or not. If it adapts, it can cause lots of trouble, since native species are, often, incapable of adapting to the invader.

If this occurs naturally, why should it be a problem? Well, simply because the rate of such events has greatly increased due to human activities. Sometimes, humans deliberately introduce a new species in an ecosystem, usually for economic reasons, while, many times, they do it accidentally. These days, while you can quickly transport any kind of item to the other side of the world, by land, sea and air, carrying some invasive organisms is a common thing.

How Do Invasive Species Affect Biodiversity?

There are quite a few mechanisms. Here are the main ones, along with historical examples:

  • Sometimes, a new species can easily prey on local organisms, bringing them to extinction, simply because the natives have no defense means. This is how the brown tree snake decimated the native bird populations in Guam. But things can get worse, destroying many local species may cause a cascade of effects that turn the entire ecosystem upside down, just like the introduction of the Nile perch did to Lake Victoria.
  • In other situations, native species are not destroyed by predation, but by competition. When gray squirrels came to North America, they started taking the place of local red squirrels. They are simply more efficient in finding and getting the food. Natives have no other option than starvation.
  • Finally, the most severe threat to local biodiversity is when the invader changes the whole ecosystem. This is especially true for vegetal species. Acacia and eucalyptus trees from Australia, or staghorn sumak from North America were introduced to various other parts of the world. Not only that they grow quickly, taking all the soil resources, but they efficiently shade the ground beneath, deterring other plants from growing. Another example is that of the highly-flammable Australian paperbark tree that greatly increased the rate of wildfires in Florida?

The big problem with invasive species is that they can affect the local biodiversity in totally unpredictable ways, and that is why such events need to be avoided.