Invasive species or exotic species or introduced species are organisms that are non-native to a geographical region that disrupts the ecological balance of the system it colonizes. The reason behind their widespread reproduction and rapid colonization of habitat is the absence of a natural predator in the region that they have invaded. Therefore, there are seemingly no obstacles in their path to proliferation. Invasive species may not necessarily be the first thought that comes to mind when talking about conservation, but their widespread significance and impact is one that needs to be understood. In the last two decades, researchers have studied invasive species, their life history traits, genetic properties, and overall impact on biodiversity. These not only reveal the role they play in the decline of native wildlife population, but also other issues like economic crisis brought on the colonized geographical region due to large scale damage, as well as spilling over of diseases to otherwise healthy animal and human populations.
Invasive species pass through some significant stages before being capable to survive in new terrain. These species on reaching foreign land, have firstly survived adverse transport conditions, after which they are able to establish themselves in the new location. They undergo a lag phase where they acclimatize themselves to the new geographic conditions, undergo modifications if required and synthesize necessary cell material. On finishing the lag phase, they enter a log phase, where there is widespread colonization which results in measurable ecological impact.
Examples of Invasive Species
Invasive species can work in different ways in an ecosystem. It can cause effects through competitive exclusion, niche displacement and extinction of native species. The Gray squirrel (Sciurus carolinensis) of North America, has displaced the Red squirrel (Sciurus vulgaris) in almost all of the deciduous and mixed woodlands of Britain. This led to food competition among the species and a simultaneous decline in tree population. They also eliminate species almost completely by Competitive Exclusion. In a detailed study in Texas, it was found that the invasive fire ant reduced the population of the native fire ant by 70% and total fire ant population by over 90%. These phenomena can be due to varying reasons like better genotypic and phenotypic traits or higher resource-use efficiency. Some highly invasive species can bring about complete extinction of native species or functional extinction wherein the number of species is too small to possess any ecological significance or role. Historically, one of the most famous examples of invasive species is the introduction of Nile Perch into Lake Victoria in 1954. The introduction was done to provide an economic boost to the fishing industry. While this goal was achieved, it brought along with it, exponential decrease of more than 200 native cichlid fish species. This resulted in changes in the ecosystem of the lake and variations in flora and fauna found subsequently.
How do such species get introduced?
Globalisation has led to increase in trade, transport, and tourism to different parts of the world. This overall boost has facilitated formation of bridges by which invasive species enter non-native habitats naturally or with human intervention. Some of the major ways by which invasive species are introduced by human sources, are contaminated cargo shipments, restoration or shipping development projects and infected instruments or gear brought to the area. Other pathways include intentional displacement and introduction of species for biological control or pet trade. The survival of these species is affected both positively and negatively due to climate change considerations, some species are able to utilise all available resources in a more feasible manner.
Recently, an invasive species Senna spectabilis has caused large scale disruption of natural habitat in the Nilgiri Biosphere Reserve. In a study done by Ferns, a nature conservation society, and the Kerala Forest Department, it has been revealed that this plant has destroyed the habitat of deer, tigers, elephants and gaurs. The leaves that are shed from the plant lead to release of certain chemicals that change the soil composition preventing the growth of naturally occurring trees. The forest floor has been rendered almost completely bare, therefore depriving herbivores of their food source. This invasive species found its way into Wayanad in the 1980s, where it was initially grown in nurseries and planted as avenue trees. 25 years later, its rapid regeneration was observed. By this time it had already spread to Bandipur and Nagarhole Tiger Reserves of Karnataka and Mudumalai and Sathyamangalam Tiger Reserves of Tamil Nadu.
Managing Invasive Species
How can we manage invasive species and mitigate its detrimental ecological impact? Early detection and immediate response are ideal as compared to managing an existing massive infestation. Complete eradication of species is not always possible, hence other control methods are employed. Biological control involves manipulation of invasive species using natural pests like bacteria, fungi or pathogens that selectively affect these species. Chemical control employs the use of herbicides, pesticides and insecticides. Cultural control is also practiced wherein habitats are modified to increase the mortality of the invasive species or limit their spread. This can include growing of pest resistant crops, changing the planting dates and use of winter cover crops. Mechanical control is employed wherein methods like girdling, chopping, hoeing, and tilling can be used. As much as these control methods are important and integral to non-native species management, awareness about the same in the public is crucial to avoid further such incidents. Educating and informing not only conservationists but also the layman can bring about a sustainable solution to this problem.
Written By- Nallur Manasa Ramesh
References:
- https://www.jstor.org/stable/2678643?read-now=1&seq=5#page_scan_tab_contents
- https://www.pnas.org/doi/10.1073/pnas.091093398
- https://www.invasivespeciesinfo.gov/
- https://www.adfg.alaska.gov/
- https://www.thehindu.com/
- Images- https://www.wikipedia.com
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