INVASIVE SPECIES

Jayantha JAYAWARDENE

FORCED SETTLERS: Every country has its own unique array of fauna and flora. Sri Lanka too has its own indigenous or native fauna and flora. Not all the native species are endemic to Sri Lanka though they are indigenous.

Some of these species are found in other countries as well. Whatever species found only in Sri Lanka are deemed to be endemic.

From time to time various species of fauna and flora have been brought into the island. Some of these introductions have been deliberate and others by accident. Such species are termed " introduced".

An introduced species, also known as an exotic species, is an organism that is not indigenous to a given place or area and instead has been accidentally or deliberately transported to this new location by human activity.

The deliberate introductions were to serve a particular purpose. For instance, flowering plants and ornamental trees were brought in so that their beauty would enhance the gardens and parks here. Some species of plants were brought for their food value, and some for scientific research.

Plant introductions include the best of fruits, flowering and shade trees, major vegetables and good fodder for cattle have been introduced into the country from time to time. Fauna or animals were introduced as pets, ornamental species and food species.

Some of the exotic flowering plants we have are the Bougenvillae, Croton, Frangipani etc. Over hundreds of years these plants have been propagated but at no stage have they multiplied profusely and taken the place of an indigenous species.

The earliest introductions of fauna seem to be the donkeys (Equus africanus) brought in by the Arab traders who sailed into this island many centuries ago.

With the capture of the maritime provinces of this country by the Portuguese followed by the Dutch and finally the British, they too brought in many species of fauna and flora.

They were called exotics because they did not belong to this country originally. In addition , a number of species have made their way into the island without our knowledge. They have come in accidentally mixed with other species, with seeds, in containers etc.

A species is regarded as invasive if it has been introduced by human action to a location, area, or region where it did not previously occur naturally i.e. where it is not native, but soon becomes capable of establishing a breeding population in the new location without further intervention by humans, and spreads widely throughout the new location.

They take over the habitats and other resources of native species by increasing their populations drastically. They are of two categories, the native and the alien.

When an exotic or alien species of fauna or flora multiply profusely and take the place of a local species, it is deemed to be an alien invasive species.

These alien species are the ones that become invasive In rare instances, native plants or animals become invasive when a change of environmental conditions or some other factor cause their ordinary population to multiply drastically and thereby suffocating the other species.

The introduction of new species can be intentional or accidental. Sometimes agriculturalists seeing successful cultivation of certain species in another country, introduced these species to this country expecting the same success story.

Unfortunately they do not look closely at the ecosystem to see what keeps these species in that country from growing to be invasive. Since this country did not have that controlling factor, they are free to multiply and become invasive.

On the other hand, they can be brought in deliberately to cause damage and problems. In other instances they can be brought in to serve a purpose and once that purpose is satisfied the introduced species continues to multiply.

A good example of this is the Salvinia (Salvinia molesta), which was originally brought in for scientific research in the 1930s.

However during the last world war larger quantities were brought in to cover our waterways so that the Japanese hydroplanes could not land. After the war they continued to multiply and choke up all the irrigation structures and irrigation canals.

Alien species are able to survive under a wide range of climatic and soil conditions, reproduce and spread at an alarming rate across the region.

This is mainly because they are free from the threats of natural enemies that keep them under control in their original habitats. They grow and increase at the expense of certain indigenous species, which as a result, die out.

In many instances these invasive species cannot be consumed as the other species and therefore the food available to the food chain is greatly reduced. This in turn degrades and reduces the habitats of many species.

In other words the term invasive is applied to species that are not indigenous or which have been introduced to the area or country, grows and increases its population to the detriment of the existing species.

Naturally invasive species would not have occurred naturally in the places into which it has been introduced. It establishes itself and increases its population.

Invasive species can change the ecological balance of an area. It can alter the economic value of an area where it has started or dominated the ecosystem and changes the manner in which it functions. Some invasive species can be hazardous to the health of the people in that area.

Once a species becomes invasive it causes four types of alterations in the ecosystem; a) the invasive species itself changes genetically as well as morphologically (in appearance ) to be more suitable for the new environment, b) it changes the species composition of the ecosystem or community it has been introduced to, c) it changes the physical features of the invaded environment through altered eco system processes and d)also makes some of the native species in the environment to change their own characteristics.

The majority of introduced species do not increase their populations significantly enough to cause much ecological change or environmental harm.

Most of these are where they exist primarily in habitats already subjected to intensive human alteration; such species are not really 'invasive'.

Species invasion has been identified as one of the major causes of the extinction of biodiversity and it is regularly discussed at the highest global levels. In countries like Australia, the introduction of cats, dogs, rabbits and pigs has caused the extinction of a number of native species.

Invasive species of Sri Lanka

A global survey of invasive species in Sri Lanka has identified 70 such species. This includes alien species as well as some native species although only few of them are well known for their invasive nature in Sri Lanka. This list includes plants, insects, mollusks, fish, mammals, birds etc.

Flora

Some of the invasive flora in the island are (Eichhornia crassipes) known in Sinhala as Japan Jabara. This species has been first introduced into this country in the 20th century by the Royal Botanical Gardens. It may have been to enhance the collection of plants there.

Unfortunately it has escaped along the Mahaweli River, which runs along the boundary of the gardens, and has multiplied unhindered. It became such a problem that in 1909 a Water Hyacynth Ordinance was passed to control the spread of this species.

The Giant Mimosa (Mimosa pigra) is a relatively new invasive species. It was found along the banks of the Mahaweli River in 1995. Now there is a thick cover for over 25 kilometers along the banks of this river.

In Kandy sand, which has been collected, from this river, for a housing project on the top of Hantane Hill, has contained dormant seeds of this species. These seeds have now germinated and the giant mimosa is spreading rapidly down the hill.

Invasive species in our protected areas

One of the major problems faced in the management of protected areas are the invasive species that are present in these parks. Different parks have different invasive species.

Invasive species are species that are not normally found in these areas but which have been brought in by accident or design and which have grown to proportions where they are difficult to control.

In Bundala NP there are two invasive species. (Proposis Juliflora called Kalapu Andara in Sinhala.) Katu Andara being the species that was there all the time. It is still debatable whether there are two different species or whether the single species has suddenly been able to proliferate at a rate it did not do before.

These thorny trees are spreading across the Hambantota and Bundala landscape like wild fire. In Bundala it has been found that all the Palu trees close to which this species has grown, are dying.

The other species is a cactus (Opuntia dillenii). Under the ADB Project this cactus is being cleaned out but it is not an easy task since we are dealing with very long and sharp thorns.

However some species like the Opuntia, that is causing serious problems in the Bundala National Park, were brought in to adorn ornamental cactus and succulent gardens. It has proliferated and is a serious problem in this park. It is very difficult to remove because of its thorns.

In Uda Walawe NP Lantana (Lantana camara), called Gandapana in Sinhala, is an invasive species that has taken over large extents of the park and has choked out the indigenous plants.

This specie is propagated by birds, which consume the berries and drop the seeds all over, which germinate fast. Here too under the ADB Project an attempt is being made to rid the park of this menace.

The Royal Botanical Gardens have introduced over 10 species of plants to Sri Lanka, which have now turned invasive.

It is spreading fast and choking the gorse bushes, which are the habitat of the endemic Pigmy Lizard (Cophotis ceylanica), called Kurubodiliya in Sinhala. The streams in the Horton Plains and other up country streams were stocked with Rainbow Trout (Oncorhynchus mykis).

The members of the now defunct Ceylon Fishing Club used fish in these waters for the introduced trout. Most of the trout in these streams have been caught or have died out. However, they have now bred in the Horton Plains and are found in the fast flowing Belihul Oya and the Agra Oya.

The Bellanwila-Attidiya Marsh Sanctuary is another area which has suffered as a result of a number of invasive species taking over there.

Invasive plant species Japan Jabara (Eichhornia crassipes), Wel-attha (Annona glabra), Podi Singho Mamram (Eupotorium odoratum), Salvinia (Salvinia molesta),Rata tana (Panicum maximum) and the Lantana (Lantana camara)

Fauna

In Sri Lanka the number of faunal species that have been introduced is not large. Three large mammal species have been introduced to the island.

As I mentioned the Arab traders brought in donkeys to the island. They were used by these traders to carry their wares to the interior of the country. The remnant of these donkeys can still be seen in the Kalpitiya and Mannar areas.

A domestic species of water buffalo has been introduced a long time ago and has now invaded most of our forest areas and mated with the real wild buffalo. Now we are hard put to find a truly wild buffalo. The only possible herd seems to be in Block 2 of the Yala National Park.

However, this has yet to be established through DNA testing. The water buffalo (Bubalis bubalis) is found in almost all the national parks. As mentioned, in Yala NP especially, it has bred with the native wild buffalo to the detriment of the truly wild buffalo.

The feral buffaloes pose a threat to the large native herbivores such as deer, sambur and elephant by competing for limited food resources, especially in the dry zone habitats.

The wallowing habit of buffaloes in water makes the aquatic habitats muddy, thereby deterring other animals such as elephants, which come to drink water. Another interesting species is the Hog Deer (Axis pornicus). There are three theories with regard to the origins of this deer.

One is that it was brought here by the Dutch in their ships, as food on the hoof, to sustain them on their sea journey. The excess animals were let off inland and made their home in these marshes. The second theory is that they were brought by the British to breed so they could be hunted for sport.

For one thing there are records of this deer before the advent of the British and the second is that this being a marsh loving deer, I cannot see the hunters suffering in boggy areas just to shoot this small deer. This theory may have come about as a result of the fact that the Hog Deer were shot by British sportsmen in India.

There are also records of two species of rats that have been introduced to this country. Introduced is too nice a word.

These rats are supposed to have come abroad some ships that have docked in Galle, Colombo or Trincomalee. They have somehow or other come ashore and bred, a thing which rats are good at.

W.W.A Phillips says that the two species of exotic mammals (R. rattus and B. bubalis) have become agents of hybridisation, where they have interbred with indigenous sub-species.

Three sub-species of the house rat (R. r. rattus, R. r. alexandrianus, and R. r. rufescens) have been accidentally introduced to Sri Lanka by ships. These have now interbred with the two local sub-species (R. r. kandianus, R. r. kelaarti) to form mixed populations.

A number of fish have invaded our fresh water reservoirs , the Clown Knife Fish (Chitala oranatus), the Tank Cleaner Fish (Ptrygoplichthys multiradiatus), the Cat Fish (Hypostomus plecostomus), Thilipia (Oreochromis mossambicus) being the most invasive amongst them.

The Thilipia was introduced as a source of food due to its high nutritional value, for the benefit of the rural poor. However it bred very fast and there was so much Thilipia to be harvested that it started the fresh water fish industry.

In Sri Lanka we have three terrestrial turtles. One is the Soft or Flapshell turtle. These soft shell turtles are also called terrapins. The other two are sub species of the hard shelled turtles, the Sri Lanka Black Turtle and Parker's Black Turtle. The Sri Lanka Black turtle is endemic.

We also have one land tortoise (Geochelone elegans). Some of the Red-eared Slider Turtle have been released into our waterways and have bred profusely. It is fast taking over from the other turtles we have.

Some of the species mentioned above and others have become agricultural pests. Five species of alien invaders are agricultural pests throughout the island.

The house rat (R. rattus) is a major grain feeding pest of rice, while the giant African snail (A. fulica) is a pest of agricultural and horticuItural crops. The feral buffalo (Bubalus bubalis) also causes damage to various agricultural crops, mainly in the dry zone of Sri Lanka.

The aquatic invasive plants Salvinia molesta and Eichhornia. crassipes are weeds in rice fields. It is possible that two others Pomacea. Canaliculata, a fresh water snail with a voracious appetite for water plants,. and Mimosa pigra, a plant that produces buoyant seed spread by water, could reach the level where they are considered pests in the near future, If we are to halt the march of these invasive species, there must first be an awareness amongst us of the serious consequences of the growth of invasive species.

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