What is invasive species?

Organisms in the natural world are constantly migrating and dispersing. Frequent human activity has caused many organisms to break through geographical isolation and expand into other environments. Organisms that occur outside their natural range as a result of migration, dispersal or human activity are collectively referred to as invasive species. Some of these are deliberately introduced by man from one place to another for their intended use and are known as non-native species, such as the American cherry and wild soybean. Most of these species require human care to survive and do not harm the environment.

However, some non-native species, including invasive species, escape into the environment and become wild after being introduced. In a new environment, without the control of natural enemies, combined with vigorous reproduction and strong competitiveness, the invasive species can invade, eliminating native species, disrupting the ecological balance of the area and even adversely affecting the human economy. Such non-native species are often referred to as invasive species, examples of which are the Brazilian tortoise.

Human use of the oceans, including fishing, aquaculture, trade in aquatic products, scientific research, navigation and shipping, can lead to the introduction, intentionally or unintentionally, of new species that would not otherwise exist locally. These species are known as invasive species, and if the local environment is suitable for their survival and reproduction, then the increase in the number of invasive species and the gradual expansion of their range constitutes an ecological invasion.

What are the dangers of invasive species?



Invasive species can lead to the decline and extinction of native wildlife and changes in native vegetation. Local ecosystems may be disturbed by invasive species eating and destroying the flora and fauna that originally inhabited them. Competition takes away and exterminates native organisms with similar food and habitat. In addition, genetic interference can occur if invasive species mate with native species and produce hybrids. Many surveys of specific wildlife may also be significantly affected.


Not only the ecological community, but invasive species can also have a significant deleterious effect on human society. This is particularly true for agriculture, where many invasive species have caused very significant losses. In addition to this there is the fishing industry, where the invasion of invasive species, for example, is another factor in the disappearance of freshwater fish.

The American Fisheries Society (AFS) states that in 68% of cases in North America, invasive species are cited as an impact factor. Invasive species can prey on native fish species, compete with them for food and breeding areas, disrupt the food chain and even introduce new diseases. Invasive alien species are a global problem, due to the growth of aquaculture, shipping and trade. The problem of invasive invasive species continues to worsen in all environments, but particularly in aquatic environments. Whether they are introduced intentionally or unintentionally.


How are invasive species managed?

What are the three principles of non-native species damage prevention?

1. 'Do not allow in': 'Do not allow in' non-native species that may have a negative impact from their natural distribution areas to non-distribution areas.

In Okinawa and Amami Oshima, there are examples of mongooses introduced in the hope that they will kill hubbies and rats, but which have eaten rare animals such as the Okinawa rail and the Amami rabbit, driving them to extinction. In addition, largemouth bass and kokuchi bass (both a type of black bass), which were released into Japan to be used as fishing fish, have been found to drastically reduce the number of native fish that serve as bait in many areas.

Alien species that are expected to have a negative impact are already regulated by law, but even non-native species may have unforeseen negative effects. It is important not to bring in alien species unnecessarily.

2. 'Do not abandon': properly manage non-native species that are kept or cultivated and 'do not abandon' (including not letting them escape, release or stray).

Green turtles are cute turtles seen at fairs, etc., but they are technically called 'loggerhead turtles'. When grown, the loggerhead turtle's shell can exceed 30 cm and it can live for several decades.

They are often seen in ponds and rivers, but are not originally from Japan. It is thought that they were abandoned because they could not be kept and bred.

As the loggerhead turtles released into ponds and rivers feed on them, native fish species are decreasing and native turtles, deprived of food and habitat in Tokyo, are causing damage to the ecosystem as they face extinction.

When keeping animals, it is important to always consider their size when they grow up and when their offspring are born. Also, never release animals into the open during the course of their lives.

3. 'Do not spread': If a non-native species is already living, growing and reproducing in the open, care must be taken not to introduce it to other areas. It is important not to spread the species further from where it is currently living and growing.