People often fail to acknowledge the distinction between simple exotic species and invasives. There is generally a negative impression associated with all exotics as being invasive and people often go on great lengths to eliminate them. According to Ch 6 in Rambunctious Garden, the words exotic and invasive are often interchanged. Most people believe that simply because a specie was introduced from a foreign habitat it makes it invasive. However, considering a proxy which fills in a missing niche and a feral cat which eliminates an entire bird on an island is too simplistic and foolish. As stated by Marris, the general impression of most exotics remains quite negative– a species invades and the ecosystem collapses, species go extinct and the complexity and diversity are replaced with a monotonous and weedy landscare dominated by invaders. However, such a point of view is quite primitive and is only valid for only a certain instances. Exotic species come in a variety of different form, and only some of them are malignant invasives.
In other cases, exotic species often increase the biodiversity of the place, help an endangered species recover or provide food for the native population. I am quite surprised that Marris does not make a distinction between invasives and exotic species. She presents examples of instances where invasives are beneficial, as well as talks about the ecological and economic consequences caused by invasives such as zebra mussels and yellow crazy ants. By definition an invasive species is the one that results in malignant consequences, therefore invasives will most likely not have any positive influences. Foreign species that help can not be classified as invasives, they are simply exotic.
Nevertheless, invasive species are a major concern and result in significant economic and ecological losses. Government agencies around the world are trying to combat the threat and have taken several steps towards hindering the movement. However, often times invasive species inadvertently find their way into foreign habitats and wreck havoc–like the brown tree snake in Guam, but most exotics often fail, die off or the natives evolve and become accustomed to them.
Another key idea Marris introduces is that of novel ecosystems– a place where exotic species have formed new ecological relationships and have become important or even keystone species. Several novel ecosystems are often a result of inadvertent human activities, but not maintained by humans. Proponents of the idea, support the involvement of exotic species and argue that they function just like or even better than native systems.
I believe the idea is practical and focuses more on the function rather than the identity of the species. Baselines and pristine wilderness is hard to establish, exotic species are present in almost every ecosystem and have become an integral part of them. Nature and the environmental process should not be interfered with. If exotic species go through natural selection and help form a balance then we should not consider them any less than the natives, and let them fulfill their respective niches.
