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ENVIRONMENTAL PROBLEMS IN LONDON CITY CAUSED BY INVASIVE SPECIES
© Kholiavko T.*
Saint-Petersburg State University, Saint-Petersburg
In this paper the effects of invasive species on the environment in urban areas is investigated. A case study of three invasive animal species in the city of London is made, investigating their origins as well as the effects they have on the city. These species are the grey squirrel (Sciurus camlinensis), the rose-ringed parakeet (Psittacula krameri) and the oak processionary moth (Thaumentopoea processionea). Several ways to reduce the number of invasive animals are proposed.
Key words: invasive species, environmental impacts, Sciurus camlinensis, Psittacula krameri, Thaumentopoea processionea, London.
Due to human intervention species occur outside their natural range. Their introduction can be intentional, such as is the case for many ornamental garden plants of exotic origins. Individual releases cause stress on native species. For example, domestic cats (Felis silvestris) cause problems in the Pacific Basin because they replace native predators and transfer diseases [1]. Another example is the release of bait fish by anglers into waterbodies. The bait fish can be a vector for aquatic pathogens [2].
However, there are some non-native species unintentionally introduced into local ecosystems. Most invasive weeds and grasses are introduced by seed contaminants [3]. Some escaped from botanical gardens like the Oxford ragweed (Senecio squalidus). This weed is a diploid hybrid species cultivated in the Oxford Botanic Garden escaped and spread throughout the United Kingdom [4].
Not every introduced species will become invasive. Some introduced species are incidentally found these are the so-called casual species. When they are able to form long living, stable populations, they are called established or naturalized species. Once the non-native species spreads into a larger area distant from the original site of introduction it becomes an invasive species. They do not necessarily disrupt the native species or the original ecosystem, but this is a possibility [5].
Case study of three animal invasive species in London. Currently there is a very diverse range of invasive species and each affects the city in a different way. Therefore, this study will focus only on three animal species that have some sort of effect on the human population within the city. These species are the grey squirrel (Sciurus carolinensis), the rose-ringed parakeet (Psittacula krameri) and the oak processionary moth (Thaumetopoea processionea). Despite the fact that they are invasive and cause several problems for other animals, local citizens
Student.
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generally love the first two species. The caterpillar of the oak processionary moth can cause severe skin irritations for both humans and animals.
Grey squirrel. Grey squirrels were first introduced into the United Kingdom as exotic pets in country-house parks and private gardens; they were imported from the eastern United States in 1876 and then spread to the rest of the country [6]. Originally, the grey squirrel is native to deciduous forests in the United States of America.
In the United Kingdom they are common visitors to urban gardens where they frequently eat food left out for birds. The squirrels are popular animals to watch in their native setting and introduced habitat and are often fed by people [7].
Impact on London. As an invasive species, the grey squirrel causes several problems for the native flora and fauna. In the United Kingdom and in London it competes with red squirrels (Sciurus vulgaris) for exploitation of habitat and food resources, which may affect breeding rates of red squirrels and reduce their offspring. In addition, the grey squirrels act as a reservoir for a poxvirus, which does not affect them, but for the red squirrels this disease is considered to be a fatal threat. Besides indirect interspecific competition, the grey squirrel shows direct aggression to the native squirrel. Grey squirrels also cause economic loss by damaging orchards, gardens and parks through their bark-stripping behaviour, taking native bird’s eggs and nestlings and digging up bulbs [8].
Solutions. The invasive grey squirrel in London city mostly replaces the red squirrel. In the United Kingdom Biodiversity Action Plan Native, red squirrels are listed as a priority species for conservation [9]. The grey squirrel has been nominated as among 100 of the «World's Worst» invaders [10].
There are several options to control existing populations of the grey squirrel such as nest destruction, shooting, trapping and poisoning with Warfarin (anticoagulant) [6, 7].
Understanding the effects caused by the invasive grey squirrel populations is important for the conservation and continuation of native species, in particular native red squirrels [8].
Rose-ringed parakeet. The rose-ringed parakeet is recognized as an invasive species in the United Kingdom. The bird was first reported breeding in the United Kingdom in 1969, and its population increased to an estimated 5.800 birds by 2001 [10]. Currently, the majority of the population is located in the Greater London area and the Isle of Thanet, Kent.
Impact on London. Like many other parrots, rose-ringed parakeets nest in tree holes and other cavities, including recesses in buildings. Naturally, there is competition with native species for nesting spots. As a result, the number of native species is in decline [11]. In 2006 the rose-ringed parakeets were responsible for two bird strikes at Heathrow airport. A bird strike is the ingestion of birds by airplane motors. The incidents at Heathrow airport in 2006 cost £20.000 each [12]. Nonetheless, the observing of these exotic birds can bring enjoyment to their owners.
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Solutions. In 2009 and in 2010 the British government issued several licences to kill the rose-ringed parakeets in order to prevent serious damage to crops and preserve air safety and public health and to conserve native flora and fauna. Limiting the amount of food given to the parakeets by humans could be a useful measure to prevent their successful establishment [13].
One more measurement to stabilise the populations of parakeets was the introduction of a permanent ban on the importation of wild birds, put into effect in 2007 the European Union (Commission Regulation (EC) No. 318/2007). Since the population of parakeets in London was already widespread when the measure was implemented, this was not effective. In areas where the parakeet is not abundant this measure could be very helpful.
Oak processionary moth. The first time the Oak Processionary Moth (OPM) was seen in the United Kingdom was in 2005. The OPM originated in Southern Europe [14]. The caterpillars of OPM are considered pests due to their danger for oak trees, human and animal health. In London attempts are being made to limit its extent and effect.
The most distinctive feature of the OPM caterpillars is the motion like nose-to-tail, forming arrow-headed groups, with one leader and following lines including few caterpillars. They almost exclusively live in and nourish on oak trees and a large settlement can strip whole oak trees bare of leaves.
Impact on London. The white hairs of the OPM contain a protein called thaumetopoein. This protein can produce mass cell degranulation and subsequent allergic reactions. This effect of the hairs is used by the caterpillars as a protection mechanism, but causes itching, skin rashes and sometimes even sore throats, breathing difficulties or eye problems for humans or animals when touching [15].
Solutions. OPM nests were revealed in the London Control Zone in the summer of 2015. Nests which were discovered had been removed and destroyed before adult moths appeared. It was done with the purpose to eliminate new nests in public places of London such as parks and gardens since the risk of contact with humans and animals is increasing [14].
A new pheromone-trapping programme was launched along with the Woodland Trust. Approximately 900 pheromone traps were placed across the suburbs of the known invaded area to catch male adult moths when they show up from pupation. These traps are being monitored frequently for moth captures from early August until September [14].
Operations are outlined and implemented by a Project Board with the Forestry Commission and Defra representatives. An Advisory Group was established including representatives of local authorities from major land-owning and landmanaging organisations, Public Health England and regulatory authorities. These groups are advised by entomologists from the Forestry Commission’s Forest Research agency [14].
Proposed measures. As mentioned before, a lot of invasive animals are due to the release of pets into the wild. Pet owners do not always think that this has nega-
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tive effects on the ecosystem and, even worse, they assume that releasing the animals will provide an ecological benefit. Therefore, communication and education is very important in order to counter this belief and to prevent such actions [2]. However, the grey squirrel and the rose-ringed parakeet are already widespread. The OPM are present in specific sites, so for this species prevention of further spread is useful.
Other preventive measurements to decrease the spread and occurrence of the above mentioned invasive species are educational campaigns that will inform the population about the detrimental impacts and potential dangers of invasive species and increase awareness. Furthermore, preventive measurements to include restrictions to take any actions that can directly and indirectly encourage development of these species should be implemented.
Prevention is not always sufficient. In this case, when species are already present in such large numbers, other measures need to be taken to stop the spread and reduce the population number of invasive species. Early detection and rapid response are needed once prevention has failed. Caulerpa taxifolia is an example of this urgency. It was detected in California and the government of California reacted immediately after its discovery. After two years, the species was wiped out. In France, the government didn’t react. The result is that it spread for thousand hectares along the Mediterranean coast and it is now ineradicable [16].
These responses might include the reduction of the population or completely destroying the invasive species in the area. This can be done by killing some or all animals by mechanical, chemical or biological means. This would be done in a humane manner if possible, without making the dying animals suffer unnecessarily. This could be done by killing them quickly with poison instead of trapping them in painful traps.
The third step to tackle the invasive species problem is management through monitoring of the status and trends of spreading invasive species, reduction of negative impacts of existing invasive species and recovery of native species and restoration of natural habitats that have been changed by invasive species [6].
Conclusions and recommendation. It has been found that the three invasive species analysed in this case study cause a wide array of problems. These range from health issue for both humans and animals to the destruction of ecosystems and property. Some of the animals might be pleasant for recreational purposes, but the positive effects do not compensate for the negative effects.
Therefore, several solutions have been proposed to reduce the effects of the invasive species. The solutions range from preventing them from entering the area to eliminating the already present animals with several different methods. In general, when combatting invasive species, it is advised to combine all these proposed measures to deal with the invasive species, in order to get the best results.
For the three invasive species in this case study, it is recommended to drastically reduce the population number of the species. This is because they pose se-
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vere problems to the native ecological system, human health and the economy. After the invasive species are brought under control, preventative measures can be taken in order to stop them from returning.
The grey squirrel can be removed from London by professional pest control officers using poisoned food, trapping, and the destruction of the nests. These methods are already tested in the area. This would allow the red squirrel to return to their original numbers in its natural habitat and remove the economic damage to the parks the grey squirrel causes.
Also the rose-ringed parakeet needs to be reduced in number due to its economic impact and competition with native species. The most effective way this can be done is by shooting them, which might not be entirely safe nor wise in the middle of an urban area. Therefore, other ways of eliminating the parakeet might be preferable considering the public opinion. Catching by hand or with nets is another possible solution. The caught birds can be kept in cages or eliminated in a humane way. Removal of the nests is another option to reduce the population.
The amount of OPM has been reduced significantly in the past in London due to efforts of the local government authorities to act quickly and remove the nests It is suggested that these practices continue in order to keep the population low and prevent new outbreaks.
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