With reference to examples examine the impact of alien species on an ecosystem.

Alien species are animals or plants that are foreign to a certain ecosystem, an ecosystem is the dynamics of a certain habitat or ecological location. Once an alien species is immersed into its new habitat it can be both beneficial and negative. Alien species or invasive species can disrupt this dynamic as each trophic level will incur an influx or decrease for example the accidental introduction of the Gypsy Moth in 1869 caused a decrease in vegetation in forests on the East coast of North America as they ate the majority of the leaves, this has an impact on both the producer, as they decreased due to destruction and the trophic level one or consumer, as other animals were unable to use this food source.  Despite this example being accidental introduction, whereby alien species move unintentionally, species are sometimes introduced to provide a purpose usually to benefit its new ecosystem, however the outcomes are often difficult to predict. As the globe becomes more mobile and accessible, alien species are more common. With the introduction of aviation and ships species can be moved to a new environment and disrupt the balance of an ecosystem.

Alien species are sometimes referred to as invasive, this suggests a negative impact of the introduction of alien species. An ecological negative impact alien species can cause is the contribution of foreign disease that native species are not immune to, for example Starling birds were intentionally introduced to America in 1800’s, they brought with them pathogens which contributed to various swine diseases affecting the current ecosystem as diseases spread killing livestock. A further negative impact of the Starling birds was the displacement of native birds, as new alien species are introduced so is new competition for food and habitats, this caused native birds to decline, disrupting the food chain as level three consumers had less to eat. Another example of this is the accidental introduction of the Argentine Fire ant in 1891, this new invasive species spread rapidly and contributed to the reduction of ant species from fifteen to just five in Texas. This suggests alien species have a negative impact on the native, pre-existing species in an ecosystem, this can reduce biodiversity as one alien species can monopolise an ecosystem.

It may seem unusual that alien species can cause economic damage as they are not as influential as human factors such as deforestation or tourism. However the overpopulation of alien species can result in large economic costs for example Deer were introduced in the 1900’s to Angel Island in the San Fransissco Bay area for the purpose of a game reserve, however they quickly reproduced and outgrew the natural food supply, thus competing with native species but starving themselves. Tourists often fed the deer and thus repopulation occurred, the problem continued until the Government had to remove the deer in a lengthy project that cost over $60,000. Another alien species that was accidentally introduced is the Zebra Mussel which was imported from the Caspian sea to the United States in the 1980’s, this alien species began to clog waterways resulting in damage that it is estimated to have cost $5million. Alien species can cause negative impacts for the animals and plants in an ecosystem but also for humans on a local and regional scale due the economic damage caused.

Whilst many alien species can cause negative impacts on an ecosystem there are positive results of the introduction of new animals or plants. Honeysuckle is an alien species in the Happy Valley region of Pennsylvania, whilst considered invasive it is actually beneficial to the area as the bird communities and honeysuckle have formed a relationship. The honeysuckle provides a food source for birds creating biodiversity as species can survive, but also the birds provide re-pollination of the honeysuckle to allowing it to continue to spread, this mutual benefit for both trophic levels is aiding biodiversity and creating a thriving ecosystem due to the introduction of this alien species.

Alien species in their nature are unnatural to an ecosystem, they will disrupt or alter the balance and dynamic of an ecosystem whether it be negatively or positively. Invasive species can cause dramatic changes in the levels of biodiversity in certain ecosystems and cause damage financially, creating a problem for animals, plant and humans. Many species have been originally introduced intentionally for a purpose such as the Deer in Angel Island however the consequences are often not predictable or thought about beforehand creating these negative impacts which could have been prevented had the species not been introduced on purpose. Despite the multitude of problems an alien species can cause, as shown with the honeysuckle example, there can be benefits if both alien and native species adapt to co-exist.