Planet earth is home to almost 8.7 million (give or take a million species) different species, with 6.5 million species on land and 2.2 million species under water. Furthermore, it was stated that an astounding 91 per cent of all species under water and 86 per cent of all species on land are yet to be discovered and categorized (Census of Marine Life, 2011). Even as many of these species are labelled as threatening, there is another category of species that is posing a threat to the ecosystem around the globe, known as ‘Invasive Species’.
A plant, fungus or animal species is termed as an invasive species if it is not native to a specified location but has a tendency to spread to an extent that it can cause damage to the human health, economy and to other species and the environment. Invasive species, sometimes known as non-indigenous, non-native or introduced species can disrupt an environment by drastically multiplying to take over a region, particular habitat or wilderness areas. Invasive species pose a bigger threat in some areas by making non-existent the natural controls of herbivores or carnivores.
The extent of damage that an invasive species can cause can be understood by taking the example of Kudzu vine which is native to Japan. Kudzu was brought to the United States in 1876 for a feature at the Philadelphia Centennial Exposition as a fast growing vine. Since its introduction, Kudzu has spread to almost all parts of the country due to the extreme rates of growth of the vine. According to the US Forest Service, Kudzu is increasing at a rate of 2,500 acres a year. While it is not only overpopulating the ecosystem, it is also increasing ozone pollution as it grows (Hickman & Wu & Mickley & Lerdau, 2010).
Some other examples of invasive species include:
- Asian Tiger Mosquito: It is known to carry viruses like Dengue and West Nile and feeds 24 hours a day. The ‘Asian Tiger Mosquito’ is native to Southeast Asia but has spread to at least 28 countries outside its native range (Gonzalez, 2011).
- Brown Marmorated Stink Bug: Native to regions in Eastern Asia, the ‘Brown Marmorated Stink Bug’ is estimated to have arrived in the United States around the early 90s in shipping crates and has spread to multiple regions of the United States, the mid-Atlantic and the Pacific Northwest. Due to their ability to eat almost anything, the bugs destroyed almost one fifth of the apple crop in the Mid-Atlantic region in 2010 (McCarthy, 2015).
Fig: Brown Marmorated Stink Bug
Image Source: Flickr
• Solenopsis Invicta- The Red Imported Fire Ant: Native to South America, these insects are known for their excruciating stings, which gives them their name. The fire ant has spread across regions such as India, United States, Australia and Taiwan. To stop the invasion of the fire ants, scientists are working to introduce other non-native species to regions which are overflowing with these ants.
Numerous invasive species around the world are harming the ecosystems and the environment and preventive measures are being deployed to curb the overflow. Geographical Information Systems (GIS) can be used to collect, store, edit and analyse spatial data which can help in decision making for officials. There are countless applications of GIS and one of it is to understand the growth and density of invasive species in particular areas. A GIS can be fed data pertaining to invasive species and it can fabricate maps for the same. These maps assist in understanding the population density and severity of invasive species in target regions. Once the results are framed, preventive measures can be deployed as required. GIS acts as a decision support system for the government officials.
The Andaman Islands is an archipelago in the Bay of Bengal. Over 550 islands come together to form the Andaman Islands which are famous for their white sand beaches and tropical rainforests. The Andaman Islands are home to numerous invasive species including the ‘Spotted Deer’, the ‘Elephant’, the ‘House Sparrow’ and the ‘Giant African Snail’, which are harming the environment in miscellaneous ways.
A study was conducted to estimate the distribution of three major Synanthropic Invasive Species (SIS) of the archipelago; viz the ‘Common Myna’ and the’ House Sparrow’. The Myna was introduced into the islands in 1867 and the sparrow in the early 1880s (Lever & Gillmor, 1987) and have spread across the islands. While the Myna is known to compete with native birds for territory, nesting sites and food (Dhami & Nagle 2009), the sparrow fights with the native birds for the nesting sites only, moving away from conflicts of food due to their generalist diet (Gavett & Wakeley, 1986).
What does the output look like?
Fig: The site-specific occupancy estimation of the ‘Common Myna’ and the ‘House Sparrow’
Image Source: Nitya Prakash Mohanty et al, 2018
The above synoptic map displays the site-specific occupancy estimation of the ‘Common Myna’ and the ‘House Sparrow’, in columns A and B respectively. As per the map, it is clear that these invasive species have spread across the Islands of Andaman in different proportions. The data was collected from 88 sites on the Andaman archipelago. The best predictor of occupancy is the distance of site to the nearest major road for the common myna, and distance of site to the nearest port for house sparrow.
Resembling the state of countries around the world, India is also struggling with various invasive species which are harming the ecosystem of the country in one way or another. According to the ‘Invasive Species Specialist Group’, India is home to 242 invasive or alien species, many of which are doing severe harm to biodiversity in India. GIS is one of the many tools that are being used to understand and eradicate the danger of overpowering invasive species.
Nitya Prakash Mohanty et al, 2018. Using public surveys to reliably and rapidly estimate the distributions of multiple invasive species in the Andaman archipelago. BIOTROPICA.