Invasive Species and Its Effects on The Entire Food Chains

Introduction

An invasive species is any kind of organism that enters into a new ecosystem and begins to negatively alter the region. Such negative consequences of invasive species include harm to the surrounding ecosystem and alterations to the habitat of the organisms already living there. Native species are generally well armed to handle the defense against other native species; when an invasive species comes along, however, native organisms are not prepared to handle unfamiliar competitors. Even worse than harm to the environment, invasive species can wreak havoc on the economy and even the health of humans. As stated by the National Wildlife Federation, a species is labeled as invasive if they “grow and reproduce quickly, and spread aggressively, with potential to cause harm”.

Immediate threats that follow the arrival of an invasive species include preying and competing with native animals, causing or carrying disease, and preventing native species from reproducing. Indirectly, invasive species may also alter the food web by destroying or replacing original sources and consequently providing little to no food source for the wildlife.

Invasive Species

Asian Carp

Some invasive species are brought into new locations to serve a purpose, like the Asian carp, but eventually become a species that is invasive. Asian carp is a common term for a group of fish that include bighead, silver, grass, and black carp. These fish were originally brought to the Southern United States to clean out algae and vegetation from aquaculture ponds and sewage lagoons in the 1960s. Environmental causes such as floods were reason that these fish were able to escape into the wild where they began to eat plankton that many other fish needed as food. As noted on the New York Invasive Species website, “Asian carp can consume 5 to 20 percent of their body weight per day… and can reach 110 pounds… dominating native fisheries in both abundance and in biomass”. Severely impacting the food web, these carp easily outcompete native fish for fish. Even further, the elimination of plankton-feeding fish takes away prey important to predatory fish in such waters. Today, the Mississippi and Illinois River systems are now made up of more than 95% of the biomass in some areas of the Mississippi Basin.

In contrast to the accidental flow of Asian carp into the wild, most invasive species are spread accidentally through human activity. The goods we use travel around the world very quickly, and these goods will often times carry species from other places into new regions. Generally, aquatic organisms travel in ballast tanks of ships and on the propellers of smaller boats. Insects can travel in the wood of shipping palettes and crates, and some invasive species start as nothing more than intentionally or accidentally released pets. Higher than average temperatures and changes in the rain and snow patterns will also enable some invasive plant species and mountain pine beetles to move into new areas.

Mountain pine beetles

The mountain pine beetle is a small bug that only grows to become about 4--7 millimeters in diameter and spreads through the movement of firewood and other wood products. Mountain pine beetles’ key to survival in parts of North America are warm summers and mild winters; this ensures that the insect not only survives, but a continuation of infestations that lead to outbreaks. These beetles affect mainly lodgepole and ponderosa pine trees, but are not shy to other pine species as well.

Mountain pine beetles affect pine trees by laying eggs underneath the bark of the tree. With the entrance of beetles under the bark, they also introduce blue stain fungus into the sapwood that prevents the tree from repelling killings the attacking beetles with tree pitch flow. Tree pitch flow happens in infected trees; “they convert a large amount of starch to sugar, which causes a flow of water from the soil into the tree by osmosis” (Kimmerer, 2014). The blue stain fungus also blocks water and nutrients from being transported throughout the tree. On the exterior of the tree, large masses of resin, called “pitch tubes,” form where the beetles have entered. Between the mountain pine beetle larvae feeding on the tree and the fungal colonization, the host tree is dead within a few weeks of an attack.

Earthworms

Another example of an invasive species is earthworms. “All of the earthworms… in the Great Lakes region are exotic; most are European” and were brought here by settlers in the mid-1800s. Today, earthworms are continually transported through the dumping of unused fish bait, the movement of compost and mulch, and any other movements of soil. Recently, researches have collected data on the dramatic changes in native hardwood forest ecosystems that have been invaded by exotic earthworms. These changes include losses of native understory plant species and tree seedlings, changes in the soil’s structure, and a decline in the availability of nutrients that the soil offers.

Because of the mixing and breaking up of the soil, earthworms are able to directly alter the soil’s chemistry. In areas that were previously free of earthworms, fallen leaves and other forest litter were taken care of by fungi and bacteria, a process that is much, much slower than the that of earthworms. This build up on the forest floor serves as a home to “thousands of microorganisms, spiders, insects, and fungi that all support the unique plant communities in these forests” (Hale, 2013, p. 5). Also important, this layer serves as perfect grounds for the seeds of plant species, most of which take up to two years to fully germinate. However, when earthworms are introduced, they eat through this layer, taking out this spongy forest floor and making it more difficult for plants to lay down roots. As a result, the diversity and population of native forest plant communities can decrease dramatically. Animals are also affected my earthworms: the loss of the forest floor takes away habitats and food sources for animals such as “nesting birds, small mammals, amphibians, reptiles, insects and spiders”. In areas with high populations of white-tailed deer, plant regeneration from feeding deer is slow and earthworms only worsen the issue.

Mussels

Another invasive species includes the quagga and zebra mussels, which are aquatic invasive species native to eastern Europe; they originated in the Ukraine and Russia, respectively. Ballast water tanks from transoceanic ships are thought to be responsible for the extended spread of quagga and zebra mussels. These mussels have caused great amounts of suffering to the ecosystems they have entered. To begin, these organisms only grow to be the size of about a fingernail. However, they clog water intake structures like pipes and screens, greatly increasing the cost of maintenance for water treatment and power plants. Ecologically, quagga and zebra mussels can potentially kill native freshwater mussels by attaching to their shells and killing them and by outcompeting the native mussels. As these mussels encrust the bottoms of lakes and rivers, native aquatic arthropods that need soft sediments for burrowing are displaced; this has even “lead to the collapse of amphipod populations that fish rely on for food and the health of fish populations has been severely affected”.

These mussels have also been associated with avian botulism outbreaks in the Great Lakes. Birds are infected with their own type of botulism, Botulism type C, which is concentrated in aquatic invertebrates that filter feed sediments or water. This has caused the death of tens of thousands of birds.

Cane toads

Intentionally introduced to Australia in 1935 to help fight against cane beetles killing off sugar cane crops, cane toads have become to be known as an invasive species. Failing to regulate the cane beetles, these toads instead began to hunt native insects. There was an initial release of 3,000 toads into the wild, but the populations in Australia have grown to be in the millions. They are now also found in south Florida and throughout the Caribbean.

In addition to eating and decreasing the population of native insects, cane toads are poisonous throughout their entire lifecycle; predators of the toads are vulnerable and die rapidly after ingesting these toads. While their predators die quickly, the cane toads are quickly reproducing. Females can lay 8,000-30,000 eggs at one time, and these eggs hatch within two to three days. In comparison, most native Australian frogs lay about 1,000-2,000 per year. As the cane toads become adults, they may compete with native animals, particularly for shelter. “A 2004 study showed that cane toads ruined one-third of nest attempts of ground-nesting rainbow bee-eaters by usurping their nest burrows and preying upon their eggs and young nestling” (“The Cane Toad,” 2010). There is unlikely to ever be a large-scale method available to control the invasive cane toad population across Australia.

Conclusion

In conclusion, invasive species enter into unfamiliar regions and take over the existing ecosystem in a way that affects entire food chains. Through both intentional release and unintentional transport, these species enter into natural habitats and take over. For native species, this means the loss of food supply, shelter, and nutrients, and over time, a permanent change in what was once known.