Invasive Species

Introduction

Defining biological invasions is challenging due in part to the proliferation of terms, especially among biological disciplines, that usually describe a set of ranging and different concepts. Depending on the author, a species in the invasion might be referred to as: alien, exotic, invasive, non-indigenous, imported, weedy, introduced, nonnative versus naturalized, endemic or indigenous. Some of the terms employed evoke anthropocentric concepts such as aggression, assault, and attack, which have normative implications. These implications and the lack of consistent uses of terms contribute to confusion (Crosby, 68).

Invasive species in general are defined as species that occupy or are in the process of occurring in regions where they have not been present historically. Specifically, invasive species are defined by their origin and distribution. An invasive species might spread into native plant communities and cause environmental harm by developing self-sustaining populations and disrupting the structure and functioning of the system. What characterizes invasive organisms is the ability to take hold of a habitat and become aggressive and dominant. It could be that either invasive species have extraordinarily wide distributions around the world, or that they are distributed locally with very high population densities affecting the endemic biota of specific regions. Invasive species are usually alien species, meaning they are able to reproduce outside their native ecosystems, and whose introduction is more likely to cause environmental harm (D'Antonio, 22).

Plants and insects are the most common orders in terms of their invisibility. From a population biology point of view, invasive plants tend to produce reproductive offspring, often in very large numbers (e.g., seeds, spores) and disperse them at considerable distances from parent plants. Invasive species also spread successfully through the use of roots or rhizomes (for example, more than 2 meters/year for taxa spreading), and such strategies enable them to spread over a considerable area. This definition also concerns species that have spread previously but not currently because of competition. These species are still considered invasive species because once local competition disappear, it may lead to re-invasion.

Massive Extinction Looming

Polls of biologists, environmentalist, naturalists, environmentalists, and other scientist report great concern that numerous species are not only threatened with extinction, but that a massive extinction is under way. Some have estimated that 20 percent of all species could disappear by 2040, with some estimtes as high as 50,000 each year. Many biologists expect species extinction rates to remain high for at least the next 100 years. Estimates are that 20 percent of the birds, reptiles, and mammals will disappear by the year 2100 (Elton, 85).

The single major cause of massive species extinction is widely believed to be human activities. These activities include the thinning of the ozone layer, global warming, hunting, farming, mining, pollution from industry, deforestation, logging, the introduction of invasive species, habitat loss, and degradation. Critics charge that the claims of massive extinction are exaggerated and alarmist overestimations derived from extrapolations based on the destruction of rainforests or other rich habitats. When asked in opinion polls, great numbers of lay people do not ...