In these chapters, Marris discuss if invasive species are as bad as we believe them to be and ecosystems that have evolved after the introduction of “invasive” species. One example to disprove invasive species are bad is Rodrigues Island. There are three rare species that live on this island: two types of songbirds and a fruit bat. Almost all of them went extinct due to deforestation of the plants. However after the introduction of exotic species of plants such as timber specie, the species grew back in numbers. Now people are removing the plants to make room for native species that wouldn’t have been able to keep the song birds and fruit bat alive due to their growth speed. Marris states that most exotic species are not harmful but we deem most to be harmful which wastes money and resources to eradicate them. That’s not to say some aren’t harmful such as the zebra mollusk. The common argument against invasive species is that introduced species tend to destabilize ecosystems and reduce their diversity. Invasive species destroy the ecosystem leaving only a few types of species left.
Extinctions are actually almost never the cause of species extinction directly. Few bird extinctions come from new birds eating food sources but killing the birds. Invasive vegetation also doesn’t exist to the complete nonexistence of other plant species. Some evidence shows islands have increased diversity such as Easter Island who had 50 native species, lost 7, but then was introduced to 68 plants after humans came.
Introduced species may not automatically complete with or prey on natives. Exotics species may increase diversity in the future. To prove this, the term novel ecosystems are introduced. Novel ecosystems are defined as new human influenced combinations of species that can function as well or better than native ecosystems and provide for humans with ecosystems services of various kinds. Examples are water filtration and carbon sequestration to habitat for rare species.
Novel ecosystems are not usually under human management except in cases where it is intentionally changed and then left to change however, and some changed by humans from a distance unintentionally, such as climate change, extinctions. It is more common to see introduced and native species living together than exotics dominating an ecosystem.
Species seem to mellow out later after decades and the composition of the species become mixed. For example, zebra mollusks dominated at first, but then were eaten by ducks that later grew in numbers.
There are reasons to keep novel ecosystems which may seem to be ecosystems disturbed by invasive species. Novel ecosystems have proven to be useful for restoration of native species. Novel ecosystems can also provide habitat for native animal species. Novel ecosystems just show signs of evolution and if one believes in that, it should be kept as is. Although species might have to be introduced directly or indirectly due to humans, we could see novel ecosystems as natures’ response to humans.
