In our modern age of extinctions, islands qualify as biodiversity hotspots. They combine the high levels of unique biodiversity, recent species extinctions and of likely future species losses (Whittaker and Fernandez-Palacios, 2007). This therefore means that protection of these hotspots is required, as well as monitoring and observing species and species interactions to prevent extinction taking place, in effect acting to conserve local species. The following post provides examples of invasive alien species in Sri Lanka, how they have come to be present and potential methods to mitigate their impact as well as remove them from society and the area.
Sri Lanka has experienced over 500 years of colonial history, in which the accidental and facilitated introduction of invasive alien species (IAS) has grown through the horticultural and agricultural trade, slave trade and the colonisation of the island by European settlers. It is during this time that many of the invasions have taken place. Introductions during this time were entirely intentional (Marambe et al., 2001). Current trends however show that this observation has shifted from intentional introductions to unintentional. This perhaps reflects the change in IAS drivers over the past 50 years. The intentional introductions were for agricultural and forestry purposes and they have now become a cornerstone for the country’s economy. Such introductions include tea plantations, rubber trees, coconuts as well as timber plants and therefore the benefits have been huge for Sri Lanka’ economy. Aside from these intentional introductions, many other species have invaded natural ecosystems or spread rapidly in human-modified ones where the consequences have spanned not only from ecological issues but economic and social issues.
Between 1997 and 2001, 34 species of alien biota were present on the island, these consisted of 13 animal species and 21 plant species, 12 are aquatic and 22 are terrestrial. The reasons behind this high level of IAS have been associated with the macroeconomic policies that have introduced in the 1970s, for example the liberalisation of the financial sector, allowing market freedom (Marambe et al., 2001). More recently, efforts to diversify the agricultural sector have resulted in private institutes and NGO’s attempting to import alien organisms for agricultural purposes. Such introductions include the introductions of molluscs to meet increasing consumer demands (which have yet to be identified) and the Golden Apple Snail, whose introduction in 1980 has been associated with the aquarium trade, originally from South America. The Golden Apple snail has become a huge pest within rice farming communities, decimating rice crops across the country.
Traditional practices have also enhanced the establishment of invasive alien species. Traditional forms of weaving have encouraged the growth and preservation of alien reeds and grasses that are invasive species of fallow marshy land and wetlands.
Intentional introduction has taken place on Sri Lanka via the horticultural industry, introducing plants to the Royal botanical Garden at Peradeniva. Such cases include the water hyacinth (Eichhornia crassipes), this plant was introduced in 1905 and enacted in 1907. Even after enactment, the hyacinth became a major aquatic weed, having both environmental and economic implications, through ‘choking’ of water bodies and damaging irrigation systems. The plant has since been mechanically removed which is a long, intensive and tedious process, however in the 1980s biological techniques were employed to manage populations, however its effectiveness was not as great as expected. There still, to this day remains no alternative technique to mechanical removal.
Deliberate introductions have also taken place by other means. Plants such as the Salvinia (Salvinia molesta), were introduced in the 1930s for scientific interests, to purify water, but has now become a major aquatic weed. There is no current information on the levels of infestation but in 1988, 8000 ha of rice fields. An eradication scheme was initiated in 1957 but was abandoned in 1964 due to a lack of funding and so the populations have been able to increase since, unchecked.
The few examples shown in the case of Sri Lanka above highlight the changes in how invasive species are introduced and how our interest in scientific investigations and agricultural advancements has manipulated the pathways along which invasive alien species have moved. These introductions have led to the decline of more sensitive species and therefore more action is required. According to Marambe et al., (2001) there is a no policy-level initiative to control the spread of IAS, this is partly due to a lack of funding, however it is predominantly due to a lack of knowledge on the consequences of the presence of IAS in ecosystems. Sri Lanka therefore needs to improve current awareness and advance scientific knowledge and understanding in the field to prevent further extinctions taking place, contributing to the many already seen in contemporary times.
Whittaker, R J and Fernandez-Palacios J M, 2007, Island Biogeography – Ecology, Evolution and Conservation, 2nd Edition, Oxford
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