From figure 1, we can see that the flow of invasive alien species is between developed countries. A possible reason for this may be that developed countries tend to have more marine trade between other developed countries. This means that species around the world can be easily transported between countries, and thus leading to invasive species in many ecosystems. There are number of ways that species can be transported around the world, as these are marine species, one likely method they can be transportation through ships. Animals such as mussels are able to cling to the hulls of ships and thus they are easily transported to different areas within the world and away from their native habitat. Another possible way marine species can be transported around the world would be through ballast water from ships. Marine animals can also be introduced in to native ecosystems deliberately due to scientific reasons. A reason why invasive may be not shown in the figure between poorest countries might be due the fact that poorer countries have minimal marine trade links between countries thus restricting the movement of invasive species.
There is significant damage that can occur from non-native species when they intrude ecosystems. This is because invasive alien species are well adapted to live in many habitats and therefore they can easily spread in to many ecosystems. As they are well adapted to live in habitats they are also able to reproduce in habitats that are not originally theirs, as a result their numbers within native habitats can start to increase rapidly and eventually start to dominate within the ecosystem. It is not only animals but invasive plant species can also disperse easily. Alien species have the ability to cause disruptions to many food webs within native ecosystems, this is because many alien species are capable of eating a variety of foods. The alien species’ better adaptations may allow it to out compete the native species for food as well as other resources. As a result, the native species within that trophic level can start to die out, and this would then continue disrupt the energy flow within the ecosystem. For example, if the native species’ population start to decline, any animal that feeds on will start to decline as well as their food sources are dying out. The number of alien species in the ecosystem will continue rise. The fact alien species lack native predators also increases their chances of survival.
Alien species affects native ecosystems through other methods and not solely by reproducing. The alien species that arrive in to native ecosystems can also bring diseases as well as parasites from where they originated from. The disease may not affect the alien species directly but can have drastic impacts on any native species whether it is a plant or an animal. The disease can start to cause animals and plants to die out over time and this is again reducing the population size of any native species whilst the invasive species continue to grow in numbers. As result of disease which can effect both animals and plants the ecosystem can collapse if all native individuals are effected. One example where a marine alien species has disrupted the ecosystem is the zebra mussel shown in the figure. The mussels are thought to have arrived by ballast water from ships, once in the great lakes, the mussels were able to out compete the native species and thrive as they lacked any native predators.
Another great impact that alien species have on native impacts is that they might be able to interbreed with species that are native to the ecosystem. One example of this occurring is between the Chinese salamander and the Japanese salamander. Here the two Chinese salamander, which acted as the alien species, was able to breed with the Japanese salamanders and create offspring; this example can be used to show the possibility of alien species, shown on the figure, breeding with native species. For example the zebra mussel interbreeding with any other species of mussel in the coast of USA.