The first thing which I understood from reading chapters six and seven in, “Rambunctious Garden: Saving Nature in a Post Wild World” is how Marris wants to elaborate on when a species is introduced to an environment the species can either be an invasive species or an exotic species. Furthermore the introduction of species into a new environment is the main cause of modern species extinction. Although they may be the leading cause of modern extinction, invasive species tend to lead to an increase in the local biodiversity, while also causing a decrease in the global biodiversity. The main thing that one has to think about when talking about introducing species to an environment is how there were natural filters that have to be kept in mind. The first filter which is what humans bypass when they add a new species into the environment is the Geographical filter. This filter refers to Rivers or Oceans, in other words something thats preventing that Species X from moving from Location A to Location B. The next filter is the survivability filter, in other words can the species survive in the environment it has been placed in, is the temperature too hot? The third filter is the competition filter, in other words can it adapt well to this environment or will the native species just be too much competition for the new species to handle.
Regarding the case of exotic species, this is what normally occurs when a species is introduced to an environment. Basically what this means is that the species will live in the environment and no drastic changes will occur to the environment. It will just live peacefully in the environment. In fact it might live so well that in some cases they may just be surrogates for old species which may have previously gone extinct.
However, invasive species are the ones that everyone hears about. This is when a species is introduced and it leads to great changes in the environment. For one thing the invasive species tend to have a faster growth rate and a higher fertility rate. This allows them to reproduce faster and thereby increase their population exponentially. Furthermore they are also used to having to compete so they’re good at it. Also, these new species don’t have any of their predators around to hinder there growth and if they are predators themselves the native population doesn’t know that they should fear this new species, not at first anyway.
Marris brings an example regarding brown tree snakes as an invasive species, she says “The brown tree snake, native to Australia and nearby countries, has killed off ten of twelve native forest-dwelling birds on the island of Guam after arriving as a stowaway in cargo ships.” She is clearly showing here how it had a huge negative effect on the environment. However, she also provides us with an example of where invasive species helped the environment such as on Rodrigues Island where two species of birds and a species of bat were dying off due to deforestation. But, they replanted the forest with an invasive tree that helped these species avoid extinction. In fact, if the trees they had planted were native they would have grown too slow to save these species, so here the invasive species played a beneficial role in helping the environment.
So, regarding invasive species they are not always bad for the environment, however due to certain prejudices that people have about ‘invasive species’ they are often not looked at with such a positive outlook. So, when it comes down to it, you really just have to see if the new species is hurting the environment, helping the environment or not effecting the environment. The problem with this view however is that if it does end up hurting the environment, it might be too late to do something about it.
