Factors Promoting Invasiveness

There are many factors that promote invasiveness and every alien species does not become invasive. It is believed that there may be some inherent features of species combined with some external factors, which promote invasiveness. Some of the factors that promote invasiveness are explained below: 

Disturbance of Habitat

Human induced disturbances include the removal of native vegetation for activities such as farming, forestry and mining. These then provide an open niche for alien invasiveness due to lack of competition and altered soil structure, availability of moisture (by irrigation), and nutrients (Randall & Marinelli 1996). Many species survive and are able to propagate very well in urban fringe environments (McNeely 1998). It is also possible that alien species exist in an area for a period of time and become invasive only after human-induced habitat disturbance. 

Frequency and magnitude of introduction

When species are introduced repeatedly in an area their chances of becoming invasive increase.

Ability to grow and proliferate

Some plant species have the ability to vegetatively propagate and produce large number of seeds. These species when fed to animals increases the chances of its invasiveness covering wider geographic areas. 

Lack of natural competitors and enemies in the new habitat

Generally, native species do not have the means to compete with aliens because they have not co-evolved with them. In some cases plant species produce substances, which are toxic to other plant species (allelopathy) or other organisms. In their own natural range, the invasive species must have survived with those plants and animals which had developed means to compete with them keeping their population in check. However the native plant species in a new habitat do not have the means to compete with them. Also, the native grazing animals or insect predators do not effect them due to their toxic metabolites. As a result these alien invasives generally form pure, continuous and thick populations.

Despite the above-mentioned factors, it is never possible to predict exactly which alien species would become invasive. Generally alien species need time to acclimatise with local conditions, and in some cases it may take decades to centuries for an alien specie to become invasive.