Within these next two chapters, Marris discussed the opposing views regarding exotic species. The argument that many ecologists and scientists agree with is that exotic species are invasive species–they take over, the ecosystem collapses, species go extinct, and complexity and diversity is diminished. Ultimately, that exotic/invasive species dominate over native species and deteriorates the native ecosystem. Regardless of whether or not exotic species are useful or beneficial, like the exotic tree species that were reforested on Rodrigues Island and revived native bird species, proponents of this argument fight for legislation and action against “enemy” species. Governmental and non-governmental efforts come at a high financial cost, though. Like Rita Beard, strikers against invasive species believe it is not a matter of aesthetics, but a matter of “saving the plant communities that have been here historically. It is also about maintaining ecosystems that can withstand the ecological changes that will inevitably occur” (101). Charles Elton’s theory states that invasive species take over native niches, as opposed to finding their own niches elsewhere, causing detrimental effects.
The opposing argument states that exotic species are truly not as devastating to native ecosystems as they’re made out to be. Dov Sax found that certain oceanic islands had increasing overall diversity due to the outnumbering of invasions over extinctions. And, “extinctions are almost never the result of introduced species” (104). Ecologist Mark Davis argues in favor of exotic species, stating that “change is the order of the day in all ecosystems, and that species move around constantly, on multiple scales” (104). Disturbance is thought to make resources–food, nutrients–more available in time. Invasive species are often times more beneficial to their new environments. Ariel Lugo found that “the exotic-dominated ecosystem was functioning better than nearby native forest, if function is measured as brute production of biomass” (113). So what really makes people go against exotic species? Marris poses the question, “More broadly, when we attack ‘invasive species,’ are we acting out of prudent caution to avoid likely extinctions, or do we merely fear and dislike any change?” (107).
Ultimately, the baseline of either argument is human interaction with nature. Anthropogenic change is either direct, as in species movement, or indirect–climate change. “Exotic pests and pathogens are introduced to control undesirable exotic species” (109). Ecologists like those who use non-native species to control other non-natives, who are against exotic species but in favor of assisted migration, are hypocritical. It boils down to the initial argument over humanity’s hand in the natural world. Once it’s accepted that man is inevitably affecting the world’s ecosystems forevermore, then the argument over exotic species seems more clear. We humans are apart of the natural world, as well. Whether some take actions like introducing non-native species or indirectly affecting areas, it is all apart of natural evolution. I am an advocate of, considerably, a “laissez-faire” environment, which does not exclude human interaction. “As the planet warms and adapts to human domination, it is the exotic species of the world that are busy moving, evolving, and forming new ecological relationships” (109). Novel ecosystems are not under active human management, but still defined by anthropogenic change. Essentially, Marris sums up my opinion of these two chapters when she says that, “We may have introduced the various parties to one another…but the rhythm of life they take up and the interplay of selection pressures they produce on one another are all up to them” (121).
