Earth Under Attack from Foreign Invaders: The Problem with Invasive Species
Updated: Sep 12, 2018
In this ever growing and constantly evolving world it’s understandable that over time we should see increasing diversity following the changes in different environments. With increased specializations, many flora and fauna have evolved mechanisms which allow them to take advantage of very specific niches in their biome. It is important for scientists to constantly invest time and effort into understanding these biological relationships in order to keep these beneficial interactions intact and develop new understandings for policy and medical advances (Sutherland, 2009).
In the tropics especially we see a great deal of diversity due to the highly variable and abundant resources packed into such a dense area. This natural process of diversifying and specializing allows for many different species of life to live together and create a self-sustaining system within their habitat. This process helps to preserve and promote the area’s diversity and allow for a sustainable structure beyond their biome, but in the overall life systems of predation, organic cycles, and natural selection.
Due to the extreme importance of diversity in the tropics, and the countless benefits it provides for sustaining life elsewhere is the world, the overall diversity of this area is under high surveillance. The most common culprit to the loss of diversity is human interactions with the natural habitats such as deforestation and spreading of pesticides (Markl, 2012). However another threat to the biological diversity of the tropics is on the rise, and it’s just as foreign to the tropics as most humans. The increased presence of Invasive Species in the tropics is seen to have correlations with the decreased diversity in areas with these invaders present (Bleach, 2014). If we were to lose a large amount of the biomass and fauna in the tropics an ecological effect would take place throughout the entire world due to the tropics key role in our biosphere. The importance of preventing and removing the presence of these invasive species from the tropics is a crucial conservation effort that will promote the growth and diversity of biological life in the tropics, and inherently the Earth.
In many areas of the tropics invading species put a stress on the environment itself as well as the native species inhabiting it. Invasive species tend to enter into communities and affect the behavior of the native species by creating an imbalance of the local ecosystem. In one study performed by Iris Bleach and her team, they saw the invasive species Cane toad enter into the Australian tropics, driving out many native frogs from their refuge sites. These sites are areas of high moisture and protection from the harsh environment that allow native frog species to thrive in times of dryness or high heat (Bleach, 2014). These native species are not occupying these Toad-inhabited refuges, and are encountering much harsher and less survivable conditions. While this is a problem for the frogs in the area, the larger scale problem is in the trophic levels. Since these native frogs preyed on local insect species and were preyed upon by local birds and larger predators, they were a key portion of the biological cycle of energy transfer. With these new toads entering the system and not filling out these roles previously occupied by the frogs, we get an increase in insects and a related effect in flora population, possible decrease in predators due to starvation and a mix up in the trophic system.
For plants, the limited number of nutrients used for growth makes partitioning of the resources so important. Certain plant species can thrive in certain conditions where the nutrient levels are just right to promote growth. The ability many invasive species have is one that permits growth even in less than desirable conditions. Since these invasive species have such a general need for nutrients, and since they are good at adapting to the environment they invaded they tend to out compete local flora for nutrients, and eventually space. A study done on the Eucalyptus plants in Brazil showed that individually the native and invasive plants grow fine, but once they were introduced into the same area, the invasive species simply out-competed the native species (Muller, 2016). This problem makes getting rid of invasive species so difficult, and is one of the main reasons why early recognition and prevention is crucial in stopping invasive species.
Brazil, however, as well as other South American countries harbor species considered invasive in other parts of the world, such as the Southern United States, Hawaii, and New Zealand. One such species is cortaderia jubata, a tall grass native to the Andes. This grass is incredibly dangerous when introduced to a new environment because it reproduces by apomixis, meaning its embryos develop without the need of fertilization. All members of this species are female and reproduce in the same way, meaning it can reproduce virtually uncontrollably. In a study conducted by Okada et al., it was found that the strains of C. jubata found in the Southern United States, New Zealand, and Hawaii originated from Ecuador (2009). It was also found that these individuals did not vary much genotypically, meaning a large founder effect was created when these species were introduced. With an increased knowledge of its genotypic variation, we have better hopes of finding a way to stop the species from proliferating.
The trouble with some invasive species is the difficulty in determining an origin, because often these species take on different phenotypes when adapting to new communities. So species can also hybridize, creating a massive problem in areas where a certain predator or parasite is already killing of a select species. Studies done in Brazil with native amphibian species show that 2 species of a fungus Batrachochytrium dendrobatidis were causing Chytridiomycosis in these species, an infection which builds up in the amphibians skin and prevents the transfer of nutrients, and also the ability to breathe (Jenkinson, 2016). The study showed that the two species had different areas of inhabitants, with the native species Bd-Brazil having a narrow range of inhabitants, and Bd-GPL which was an invasive form of the fungus. With the hybridization of these species, we now have a more resistant local fungus which can withstand certain environmental pressures it could not before, effectively making it harder to get rid of. This case is not uncommon and produces many hard to kill invasive species.
It’s easy to see in the environment how animals interact differently with one another, and how the substitution of a species can impact that ecosystem dramatically, but animals aren’t the only kingdom with unwanted visitors. Plants can also have uncommon or non-native species enter into their area, through means of chance, animal transport, or human manipulation. Usual human interactions with the forest such as deforestation, logging, and milling cause giant gaps in the forest. The obvious loss of an oxygen-producing life forms and loss of animal habitats is a huge concern, but even once the trees start growing back another problem may have started. Invasive tree species enter into large gaps easily due to the large opening for plants to start to grow and the increased sunlight made from the loss of the canopy (Benitez-Malvido, 2003). The soil disturbance caused by deforestation also prevents the native trees from growing because they will not be accessing nutrients the same way, another reason invasive species have an opportunity to grow (Joshi, 2015). Since invasive species are shown to be damaging to ecosystems and these invasive species are most easily found in areas of great forest disturbances, it shows that with less human interaction with the forests, we can help prevent these invasive species from impacting the ecosystem.
In 2001, an initiative in Panama was started to control the feral dog and cat populations within the country. Spay Panama, a volunteer organization that spans the country, spays and neuters feral dogs and cats in order to maintain and decrease their numbers. Now currently headed by Mississippi trained veterinarian Dr. Isis Johnson-Brown, the organization employs volunteers and veterinarians alike to help control these out-of-control populations. Feral dogs and cats are invasive to the Panamanian environment, and are dangerous because they can carry diseases like rabies, and can infect more endangered local species.
These feral animals can also cause a decline in native species due to predation. Domestic cats, for example, are excellent hunters, and have been known to cause huge declines in amphibian, reptile, small mammal and bird populations. Abandoned house cats are one of the most damaging species introduced to islands in particular, and are the primary cause of extinction for at least 33 insular endemic vertebrates. A meta-analysis of 72 dietary studies based on the stomach and scat contents of cats show at least 248 species from 40 islands worldwide were preyed upon by the feral felines (Nogales et al. 2013). Since the domestic cat has such a wide range of prey options, this could spell certain doom for many endangered and endemic species found throughout the world. A rapid decline in such primary consumers could cause and has been causing dramatic changes in ecosystem stability throughout the tropical mainland and islands especially.
As more invasive species are introduced to foreign areas, more creative methods of controlling and eradicating their populations must be employed. Bivalves are notorious for their ability to stick to any hard substrate – manmade or natural. Years ago, zebra mussels entered the Great Lakes via attaching to the hulls of cargo ships from Asia. Since then, they have dominated both the native species and the infrastructure of the lakes. Invasive bivalves can colonize the shells of native bivalves such as other mussels, clams, and oysters, sometimes to a point where they can’t even open them to feed, thus killing the native species. They also consume a large and vital portion of available zooplankton that native fish and other larval animals need to survive. In regards to infrastructure, these bivalves can clog water intake pipes and boat rudders with their rapid colonization abilities. Methods to dispose of these colonies are costly, and include pressure washing, thermal decontamination, desiccation, and on rare occasions chemical decontamination (NOAA 2016).
To approach this issue in a novel sense we must understand the mechanisms that invasive species use. Since we cannot eliminate those introduced by natural disasters, we need to take time as ecologically responsible people to check for our possible contamination of water systems with invasive species. Many programs are setup to help alert people to local invasive species, and lays out instructions on what to do if one finds or catches one. I feel more systems of education like this one can help combat the medium that most invasive species use: humans. Our commercial trade with other countries through water, air, and land opens so many paths for invasive species to come in, so understanding how to check for, identify, and eliminate invasive species is critical to preventing their effect on our biodiversity.
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