Introduction of exotic species: causes and consequences

The exotic species (introduced, non – native or foreign) are those species that have been introduced in an area that is not within its natural range.

Its establishment is not always easy due to the characteristics of each ecosystem, which in themselves represent a set of filters that the new species must overcome in order to settle in it. They can only achieve this if they are able to reach these new areas, survive these ecosystem filters and reproduce.

Once the filters have been overcome and settled, these species may or may not cause damage to the ecosystem they have recently accessed, that is, exotic species do not have to pose a problem per se . An example of this are potatoes or corn, originating from America and that do not cause an environmental impact. In the case in which a species causes alterations in the habitat of the autochthonous species (inhabitants of that area naturally) it becomes an invasive species .

Invasive species can be both exotic species and indigenous species . They become invasive when the increase of their individuals produces changes in the ecosystems to which they access, both at the composition and structure levels and at the level of the processes that occur in it.

What happens with invasive species is that the species present prior to the invasion, not having co-evolved with them, are not capable of competing for resources, and may end up displaced or, in extreme cases, dying and becoming extinct. Therefore, these invasive species can be detrimental by endangering the biodiversity in that particular area.

It would be the result of the combination of the two previous sections. An invasive exotic species is, therefore, a species introduced artificially, accidentally or intentionally in an area that does not belong to its natural distribution and that finally overcomes the filters of the ecosystem by adapting to it and managing to invade it. Generally, invasive alien species have a negative connotation since they tend to be very harmful to the ecosystem , being considered one of the main causes of the loss of biodiversity worldwide.

Alien species can be introduced for a variety of reasons and ways. The main reason is the trade in exotic species , but tourism and transport are also among them, such as the zebra mussel, transported in the hull of the boats without their presence being noticed.

On the other hand, they can be accidentally or intentionally introduced to be used in activities such as hunting or sport fishing (an example of an animal species used for this purpose is catfish), gardening, their use as pets, which are later they abandon and reproduce successfully (such as Argentine parrots, raccoons or Florida Galapagos tortoises ), in fur, scientific reasons …

The introduction of invasive alien species (we make this distinction because, as we have said, alien species do not have to be a problem in themselves) causes major disturbances in the biota of ecosystems, which is aggravated by other environmental problems such as be deforestation , contamination of soils and aquifers or transformations in the territory. What this produces is that the imbalance that causes the mobilization of all these species in the ecosystems cannot be corrected naturally due to the speed of the process.

Not all introduced species will wreak great havoc on relationships between other species, since many will not be able to adapt to the new environment and will not survive. However, those with a greater adaptive capacity will do so , even causing the denaturing of the ecosystem and the loss of biodiversity due to the death of fundamental indigenous species that are displaced by new arrivals. As a result, an ecosystem is obtained in which the species have no relationship with each other.

There is another damage more associated with the economic level. There are serious direct effects on agricultural activities and public health (for example, the Asian wasp , Vespa velutina or the tiger mosquito, Aedes albopictus ). Invasions are difficult to control and eradicate, being costly and not always possible. The best solution is to identify possible invasions of these potential invasive species to prevent their growth from becoming a problem.

In Spain there are many invasive species from all kingdoms of living beings (plants, animals, protists, fungi …). All of them are listed in the ” Spanish Catalog of Invasive Alien Species “, approved by Royal Decree 630/2013.

Some examples of invasive animal species in Spain are:

• Tortuga from Florida ( Trachemys scripta )
• Bullfrog ( Lithpbates caestbeinaus )
  
• Gray or Argentine parrot ( Mylopsitta monachus )
• Kotorra de Kramer ( Psittacula krameri )
• Mapache (Procyon lotor)
• American mink ( Neovison vison)
• Red crab (Procambarus clarkii)
• Siluro (Silurus glanis)
• Greek partridge ( Alectoris graeca )
• Common carp ( Cyprinus carpio )

On the other hand, some of the invasive plant species in Spain are the following:

• Ailanthus ( Ailanthus altissima ), which is found in the vicinity of roads as an “ornament” and which has great destructive power.
• Cane ( Arundo donax )
• Common water hyacinth ( Eichhornia crassipes )
• “Duster” species (of the genus Cortaderia )
• Black bamboo ( Phyllostachys nigra )
• Calendula ( Arctotheca calendula )
• Chumbera ( Opuntia ficus-indica )
• Mimosa (Acacia dealbata)
• Eucalipto (Eucalyptus globulus)

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