Non-Native Species --- A Brief Account
Table of Content
Aim of Website
"Humans are omnipotent. This thought is not to be encouraged, but here we stand, above all the other fellow organisms in the world. We do not know how many species of organisms there are, but we do know a few particularly well. And we have been particularly kindly in bringing them around the brave new world to travel and experience all of this novelty --- not to mention the dear price some of these have to pay. But we have been generous captains, chauffeurs and pilots. And we did not refrain from being most charitable. We have shown ourselves to be fulsome imbeciles that have muddled up reality, turning it into an imbalanced fairy tale of destruction."
This sketches how the non-native species have come by. In this website, we will investigate the crooked path through which non-native species trample upon in the forest of life, the alien vessels in which they travel, and answer the 'what's, 'how's, 'who's and 'now what's about these fellow inhabitants of the beautiful planet we are living in, finally leading us into the practical actions we should be taking unless we want to watch this beautiful planet's vitality succumb to a giant tangible mob of involuntarily defected brethren. The problem of non-native species is subtle as well as blatant, far-fetched as it is related to our daily lives, and somehow direr than we may be led to think. We will soon see why this is so, and explore possible solutions to the problem, which in turn will lead us back to the appreciation of the severity of the problem itself as many attempted measures of dealing with the ongoing crisis with non-native species have culminated in disappointment.
Introduction to the term Non-native Species
A Non-native Species (NNS) is generally defined as an organism peculiar to a specific area, which can cause environmental, ecological and economic impact with their introduction; or alternatively an organism occupying places beyond its historic range, colonizing ecosystems from which it has been absent all along. This is roughly synonymous to the terms exotic species, introduced species, self-sustaining feral species or naturalized species. The non-native species that are, in effect, particularly active and voracious in displacing indigenous ones, being capable of outcompeting them, are termed invasive --- which in many cases turn out also to be agricultural pests causing substantial economic loss, viruses that threaten public health in periodic outbreaks, or invisible predators that leave us with little wildlife in the countryside ultimately. We will emphasize on the environmental and ecological aspects of such introductions, pointing out how these introductions affect the effective functioning of ecosystems and how these affect humans and the world as a whole.
It is worth pointing out that the negative connotations of the term are quite well grounded for reasons that will present themselves in the following sections. Non-native species can be either beneficial or malevolent, but most have a status that is largely ambiguous; most crops and livestock that have circumglobal ranges are non-native species, and are economically beneficial to humans. In this case the introduced species are largely domesticated and modified, so that they could be nowhere like the original form --- wheat, banana tree, domestic fowl and pigs are good examples. In this case it is important to realize that most of the ecological impact can be attributed to human use, and not to these keystone goods of the economy. Therefore it is sensible to take non-native organisms in the specific sense, dealing mainly with the invasive species that merit immediate concern, as the scale of the current problems are unprecedented --- we shall see why presently. Under all conditions the criteria for an organism to be exotic to a particular area are clearly defined, and will be expanded in the next section.
# Whats and Whys
What is a non-native species?
Non-native Species are not found naturally and are "foreign". You may ask what it is meant by that, for it simply sounds esoteric the first time the phrase is came across --- for when due consideration is given to our definition, we find that individuals can be peculiar to a place but it is hard to imagine a whole species of organism being so --- at least, not for widespread species like the Barn Swallow, House Mouse and Mackerel, which seem to be so abundant that their range cannot be definitively stated. What makes a non-native species non-native? The question is certainly complex, but as we attempt to delineate the key criteria here, it will become apparent that the ambiguities must be taken into consideration when the problems associated with non-native species are to be dealt with.
This is exactly why we must consider two important concepts to clarify the definition of non-native species. These are natural range (and how this is defined) and means of dispersal --- which leads directly into our central area of concern, the unconscious generation of the non-native species concept. More of this will be discussed in the ensuing section.
Ecologically, there are two extreme roles an organism could adopt in their struggle towards survival, and the human society could be seen as working on a similar principle. In our society we have professionals on one hand, which specializes in one job and usually focuses on perfecting their professional skills. Some people will have changed several jobs before they eventually settle, and some keep on shifting their occupations, widening their scope of adaptations and gaining certain levels of proficiency in many professions. In nature, a graduation of ecological specialization exists, though the range is far more radical and dramatic, while the forms are subtler than that in our society, so obscure that biologists are still a long way from understanding some of the basic mechanisms of how these stratifications come into existence. Specialization and generalization determine the natural range of many species and correlates with the topic of NNS rather intimately. The diversification of organisms in the world in adaptation to their environment, which includes both the physical conditions such as temperature and rainfall, and biotic factors --- by which is encompassed all the other organisms coevolving with that in concern, is termed niche specificity. Generalists are the constant job switchers, straddling a number of available niches --- though not reliably attributed to a specific role, the catholic choice of habitats and food sources characterize these species, and often proffer them auspicious opportunities in times of severe crisis owing to their adaptability. They are not confined to narrow niches but are more open to radical changes in the environment, and are more likely to survive in new environs and alien territories, in many cases establishing themselves --- outcompeting the established tenants as introduced species.
Specialists by contrast have confined niches, which can be effectively seen as analogous to professional fields in human terms. They tend to show unique adaptations that are not easily transcended by other latecomers to the habitat that possesses equally special conditions, either due to the seclusion of their environment from the outside world, or that the presence of many distinct niches have enabled the development of specialist organisms that fill these niches. For example, some hummingbirds of South American rainforests have coevolved with heliconia (a flowering plant) that produce their favourite nectar, and many pairs of these have become so mutually specific in that the plant relies solely on the hummer for pollination, as special shapes of petal tubes allow only certain species of hummers with a complementary bill shape to exploit their nectar while acting as pollen vectors simultaneously. When the food source of specialists is removed, the chances of their survival are drastically reduced. Therefore specialists are generally less adaptable to changes in the biotic composition of communities in their habitat and are vulnerable to non-native species invasion.
The difference between the two broad roles is exemplified by the difference in natural ranges, or distribution, of the organisms. We can infer from the last example that the hummingbird species that live particularly on the nectar of one species of heliconia occur only with the flower, and it follows the range of the hummer is restricted by that of the flower. There are organisms that live nowhere else but in narrow habitats in which particularly special physical conditions prevail, like the blennies and bacteria that live around the hydrothermal vents in the depths of the Pacific. Range restrictions can therefore be so extreme that in the case of some, like the Stephen Island Wren in New Zealand, from an island that has an area of only 1 square mile, the range is too tiny to allow breathing space for the species when alien invasions occur, as indeed transpired --- the species was wiped out by a single cat.
Too much about the victims; in general the range of all species are defined roughly through mainly geographical barriers, control and competition from other organisms, and such physical factors as climate, elevation, salinity, temperature, and the like. The world is divided into several belts, or biomes, in which the dominant vegetation prevails. This determines to a great extent the fauna found in that biome, both on land and in the sea. The vegetation type is mainly determined by the mean temperature and climate of the region concerned: the cold, dry polar areas are denuded, while further towards the equator, as the temperature rises, the vegetation changes from tundra, savanna, taiga forests, deciduous broadleaf forests and tropical rainforests, roughly. The ocean also varies by region in productivity, species diversity and type of vegetation (algae) and this is ultimately linked to the temperature and other conditions of the environment. Organisms are more or less suited to a few of these regions individually, and they have different ranges according to their life requirements. Geographical barriers are more easily envisaged as fences that mark the viable territory of a species as an entity. Barriers could be ill-defined, such as patches of unsuitable habitats shunned as a rule, considering rainforest specialists that find it hard to cross exposed roads that bisect some of their home ranges Amazonian Marmosets (small ornate primates that live in the canopy) cannot cross some of the larger tributaries and have especially narrow ranges, as they are so dependent on their homeland that they could not bear the stress of breaching their limits to seek out other possible haunts. The Pacific is the end of the world for many endemic islanders, apparently, and it is not hard to see that though birds and insects are endowed with the power of flight, many island species have lost the aptitude in this respect as flight became fairly redundant in predator-free habitats. Mountains and deserts are apparent blockades to the pioneers.
What this all lead to is that every species on earth has a natural range. This is not a static boundary restricting physically the movements of organisms as is sometimes thought, but rather a dynamic region in which the organism could normally be found in its natural state, which is defined by factors briefed above. Organisms are supposed to thrive only in their natural range due to the presence of favourable habitats, regular food supply, or the fact that in many cases other similar havens are inaccessible beyond the barricades that impede a species from emigrating and establishing themselves in these foreign lands to which there already are a set of rightful inhabitants. City-dwellers may find it difficult to cope with the featureless, uneventful life in the countryside; those living in the rural areas could be daunted by the stress and clamour of city life, and adaptation to such may be unfeasible for them; more radically speaking, the indigenous people of remote African tribes would be doing the exceptional to be successfully tackling with the pace, style and demands of life in modern civilizations. Yet the cream of the crop do --- adaptive organisms, and let us say NNS, stand a much better chance in the race of evolution, but it is not without the instigative efforts of humans that they could put other organisms out of existence. It is the presence of order that allows disorder to take its toll --- and this is what the NNS problem entails.
Means of Dispersal
The diverse plethora of life on earth has been interacting with the environment they are living in for billions of years. Today we are fortunate to witness this dynamic diversity of life at play and it is particularly miraculous to play a part in this dramatic panorama. However, the very differences, exhaustive to name, amongst these organisms serve to constrain most of them to specific habitats. There are less obscure criteria than habitat preferences and biotic interactions that determine the natural range. Effective physical barriers often delineate the range of some species by the direct blockage of dispersing individuals, for example deserts, mountain ranges and rivers. Species that have a vast natural range either have fortuitously crossed from continent to continent in times of severe gales, utilized drop in sea level that exposes land bridges, or in times of climatic change happened to possess certain characteristics that enabled it to outcompete many of its congeners, allowing it to proliferate. For oceanic species it is even less obscure as the continuity of the seas leads to free dispersal, and the range of oceanic species is determined mostly by their physical tolerance of water temperature. Circumtropical and circumglobal distributions of many Whales and some Sharks illustrate this point. Introduced species seldom applies to the vast ocean, but local shorelines can be prone to infestation, as many organisms thrive in estuaries and tidal zones, and are restricted largely to these areas that are comparatively tiny in area to the ocean.
How do land species disperse? We may note that naturally organisms disperse, and their ranges are ever changing. To colonize new sites the fluctuations in environmental conditions must favour the spread of the organism to previously unpalatable places, and such has happened with Crows that seem to be spreading in the Malay peninsula, presumably due to more scavenging opportunities with the increase in human population, and thus, rubbish dumps; the end of the last glacial period 10000 years ago have enabled trees to recolonize the boreal lands after a period of coldness that saw ice sheets expanding down to Central Europe. For migratory birds and insects the ranges are ill defined --- their extreme mobility and propensity to travelling often causes vagrants to turn up in unexpected places, but these do not normally turn sedentary afterwards and is hardly called dispersal. The idea is that every species, plant and animal alike, have their own levels of mobility and interactions with the environment, or rather dependence on certain habitats, that natural dispersal is limited. Under normal conditions no species could occupy every single spot in the world (with inconsequential exceptions) though some achieve cosmopolitan range --- not meaning that they have penetrated every ecosystem available. There remains inaccessible environments thus for every species of organism, which either are unsuitable to their survival, or not so, but nevertheless physically inaccessible. Plants in the Pacific Islands can disperse with seeds that float on water and travel around the island groups, yet not many succeed in germinating, for the soil conditions where they bump into solid ground may be deterrent. The limitations spelt in the previous section thwarts natural dispersal.
Humans are special. It can scarce be denied that for the single ability of him to transport goods on a global scale merits the claim. We have sighted ourselves as distinct from other animals, and have viewed them as goods. With technology from steam-propelled ships to aeroplanes, we have taken the flow of necessities and amenities to such a scale that could not find rivals across the globe. These transport vessels breach almost all barriers, and previously inaccessible, rich habitats are made available to the travellers that used us, or those which are use by us. Human-aided dispersal defies all natural boundaries, and may be direct or indirect. Direct transport explains itself; but in the process of altering the environment through agricultural development, changing forests into plantations, constructing concrete banks around the rivers, and other activities as such, man also indirectly cause habitat changes --- forests are cleared into huge tracts of arable land, heaths are burnt down to create farmland, wetlands are drained to give pastures, and so on. This enabled some organisms to expand their range exponentially and push others to the brink of extinction. The eviction of natives by generating habitats favourable to others can augment the population of the protégées to pest proportions --- this is particularly true in introduced agricultural pests in places where monoculture has taken place. There are also instances where introduced animals change the landscape so much that natives are driven into isolated patches of relatively untouched habitats, and the remaining is colonized by other introduced species as a result. Grazing animals such as Goats can easily denude islands of their native vegetation, reducing habitats for native species while enabling other introduced species, such as Rabbits and Weasels, to infest upon the plains that have been opened up. The insidious effects never cease until the introduced species are eradicated.
Causes of NNS Establishment and Spread
It is wise to learn from history, and the extent of non-native species problem cannot be underestimated as before. Humans may not be aware of this centuries ago when widespread introductions began with the explorers that poured out to Oceania and the New World --- in fact Europe has already been under tremendous pressure from introduced species then, but the effect was not as apparent as that of habitat destruction, attributed again to an introduced species homo sapiens. We have two main focuses here: one is why NNS have turned up where they should not have in the first place; the second is why have they have spread, and not been eradicated by other organisms in the introduced range or degenerated to oblivion on themselves.
We have seen the advancement of transportation in the past centuries, and in the packs and freights of our crafts have been found many hitchhikers indeed. This is what accidental transfer of organisms are all about --- many of the hardiest invaders have gained access to the remotest island and other continents through human transportation for no reason, and amongst all the Rats must be mentioned, which have been spread throughout the Pacific Islands in this fashion, especially the Black Rat, alternatively named Ship Rat, for its ability to cling to ropes and hide under decks in ships. A researcher in Massachusetts accidentally released Gypsy Moths that he transported there to conduct studies upon, and we may safely assume that it would not be a single incident. Accidental introduction have spread the most pernicious NNS around, as any organism likely to survive the long journeys, scarcity of food and physiological stress of the alien environment are likely to be the most adaptive of all, and when they parachute upon pristine habitats, they and their avaricious descendants can tip the balance of the local ecosystems with stunning swiftness.
Most introductions, however, are not accidental.
It is surprising that how many species are introduced from the affection of humans towards animals. As it turns out, many of the pets are not kept at home, and the nostalgic urge of many colonizers to the Australasian area have brought along European birds and mammals with them, resulting in effects as serious as transformation of some parts of the landscape. Cats, Dogs, Rabbits, Starlings, Goldfinches and Slider Turtles have been introduced for this reason, and when let loose, have presented dire challenges to the lives of many of the fragile ecosystems whose collapse we have witnessed.
Many plants such as orange, banana, potato, rubber tree and the like originate from the tropical countries. Plantations in those countries are simply insufficient to satisfy the world demand for these important crops and some of the food crops have been introduced to the developed world and intensive farming methods are adopted to wring as much yield as possible. Livestock such as goats, sheep, cattle and pigs are also widely introduced into ranches created out of prairies in the Americas and tropical forests in the Pacific Islands, so that a few are virtually denuded. The benefits of such introductions gave rise to the pillars of modern economy, and who could say what the world would still be like without the widespread cultivation of potatoes, wheat, rice, and the rearing of livestock as cattle and sheep?
3. Control of pests
Biological control agents are organisms that are deliberately introduced to control pests. They are highly predatory, usually specializing in feeding only on a narrow range of prey species, and are preferably efficient in keeping the population of the pest species at a low level through natural predation.
Ignorance about the biology of certain introduced controls have unleashed some of the most invasive exotic species as these predators, if non-discriminatory in taking prey with generalist feeding habits, can reduce the numbers of many keystone members of the ecosystem as these may not be accustomed to this novel source and mode of predation. Rats are known to kill Albatrosses, which are large seabirds growing to 90cm in length for medium-sized species, alive when the birds are incubating on islands; native marsupials of Australia have little defense against the introduced foxes that prey on them, while the foxes had been expected to control the burgeoning rabbit populations; the list can be expanded for sure. Successful attempts of biological control are scant, but the method is currently widely explored and researched as a potentially far more effective alternative to applying pesticides to crops badly affected by uncontrollable pest infestations. Good biological controls only eat the pest naturally, and can be effective in preventing large-scale crop loss to pests and use of toxic pesticides that pollute the environment.
4. Environmental Improvement
It is awkward that this should become a category as often this encompasses the rectification of problems caused mostly by humans, and the appeal of many plants to our aesthetic sense. Many tropical plant species like orchids are introduced as pot plants, and the sausage tree (native to Africa) and pencil tree (native to Asia) have been introduced widely as ornamentals. Some widespread ornamentals have turned out to be a great nuisance as they begin to displace native plants by competition. The Brazilian Pepper Tree (Schninus terebinthifolius) has been introduced to South Florida for use as a landscaping plant, and since have been dispersed so widely by birds that feed on their berries, they have jostled many native species out of place. Australian Ironwood (Casuarina sp.), mistakenly purported to be capable of draining flooded swamps to yield available farmland, have also been introduced to Southern Florida and they turn out to be shallow-rooted and despite having been spread widely they collapse easily around coastlines and expose the fragile shores to cyclone, causing similar degrees of trouble as many other introduced plant species.
Present agricultural methods have caused soil erosion in many places as after harvesting, and the stabilizing ability of their roots on the soil is sporadically deprived of. Kudzu trees (Pueraria lobata) and many others have been grown around such agricultural areas, reputedly to alleviate the effects of soil erosion, as their roots are perhaps more efficient in soil retention than most other species --- but in terms of survival skills they are certainly superior. The deep-rooted Tamarisk tree (Tamarix mannifera) helps combat soil erosion, but its displacing effect on local plants is also great, causing radical changes in the species composition of the new habitat, and with the local plants are gone the animals that depend on its fruits and various other ecological services for survival.
Having seen the main causes for introducing new species into an environment, our second question would be how the NNS are allowed to spread. Certainly to an organism's survival some factors must hold true; the physical conditions of the new habitat must be allowed within the range of physical tolerance exhibited by the species, or rather, extremely competitive individuals. Once the invaders have gained a toehold, it is usually not difficult for the more adaptable species to continue spreading. The habitat type available determines the success of introduced species; if there are large tracts of disturbed tropical forests, vines can find their way in easily if natural predators are not present (some mites and thrips specialize in feeding on the vines, but these are found in the native rainforests only), and the freshwater systems that are in essence equivalent to counterparts across the Northern Hemisphere have allowed many Eurasian freshwater fish to infest upon the Great Lakes, where similar habitats occur; the North American Largemouth Bass (Micropterus salmoides), in turn, have found the habitats of Lake Titicaca in the highlands of Bolivia and Lake Atitlán in Guatemala quite idyllic --- these lakes are notorious for the loss of biodiversity through habitat destruction and the introduction of freshwater species that endangers the other inhabitants, mainly predatory fish as the Bass We must mention some of the failed introductions to exemplify the fact that not all attempts as such are successful. The Chinese Bamboo Partridge has been introduced to Hong Kong but efforts did not produce viable populations that can sustain themselves.
Disturbed ecosystems are prone to invasion. This is a general rule, and may be too general, but it can be imagined that with the increase of pollution and disturbance to the New World and some remote tropical countries or islands that picked up speed in the last century, species not used to the dominance of men may find it exceedingly difficult to maintain original population sizes as the resources and space are reduced from competition with humans. They can be more prone to NNS that have considerably adapted towards lifestyles that allow them to coexist with humans. They are more open to human disturbance and have evolved corresponding measures against decimation but the natives have not, having also been weakened by direct human influence. This is why the NNS problems often come hand in hand with alteration of the habitat, clearance of forests, and various human activities that degrade the environment. However, conventional wisdom about introduced organisms has proved tenuous in a way, as researchers have found that even healthy ecosystems are prone to invasion. The traits that certain ecosystems exhibit may be encouraging to invaders, with plenty of excess resources for the introduced species to utilize, and not many competitors to curb the spree of the raiding alien species.
Even if predators and competitors are present, those NNS that we see with self-sustaining, or ceaselessly multiplying, populations tend to possess certain weapons that help them parry assaults or even launch powerful counterattacks. One of them is high fecundity, which is the ability to reproduce profusely or rapidly, or both. Mice are fast breeders; their populations can expand tenfold in several weeks, given a surplus of food and enough shelter, which habitats altered by humans often offer. In many cases the NNS that have established themselves are those who can grasp any opportunities of reaching food sources, and are, as mentioned, generalist feeders, meaning that the total amount of food (to put it simplistically) available for the species within a given period of time exceeds that of its competitors, giving the NNS a comparative advantage. As a result they are hard to eradicate due to the sheer numbers present. Resistance against predators is, last but not least, one of the common characteristics of successful invaders, as they either produce toxins, like some Toads and Plants, or are unpalatable with inaccessible nutritious parts, perhaps exploited back where their origin lies but not in the heavenly colonies into which they have poured, where the new neighbours have yet to learn how to tackle them.
The reasons that some non-native species become established in certain areas only are still largely in mystery, but certain factors must be limiting their range in the foreign lands under the same set of natural rules that govern the range of species in their natural conditions.
# Species Accounts
The problem of non-native species has been rated the second most important threat to biodiversity, after habitat destruction by humans, according to the IUCN. There is no doubt that many introductions have resulted in disasters and unwelcome homogenization of so many valuable ecosystems that altogether works to maintain a diversified, multi-functional world of life with intrinsic, practical and aesthetic values.
Human have been such a successful vector of exotic organisms that the populations of many of our commensals have become globalized, and there are no countries that could be exempt from the adverse effects of the phenomenal immigration of these organisms. Many cities are now invested with Pigeons whose excrement pollute the cityscape; outbreaks of mice were not uncommon at the turn of the last century, and the silent onslaught of garden birds, depleted fish stock in lakes, patches of noxious weeds choking out other plants and the familiar fauna of urban areas in Honolulu are just a few examples of the increasingly discernible presages of more serious effects of ecological imbalance as the new millennium shines through the clouds to find us amidst the most disastrous of acute environmental catastrophes in millions of years.
We will present a selection of the most influential NNS in this section to give a picture of what the situation is like and how the invasion is getting on. The species portrayed in this section are the soldiers of an army stampeding across the world, having crossed the gangway of vessels we have captained onto uncharted territory of milk and honey. Representative species from all major vertebrate groups feature in these profiles, as well as other less conspicuous species, which nevertheless contribute to no less disastrous effects than the 'mega fauna' of the present day --- humans, who had had them teleported to the wrong universe in the first place.
Please choose from the following catagories:
1. Animals > Vertebrates > Amphibians
2. Animals > Vertebrates > Birds
3. Animals > Vertebrates > Fishes
4. Animals > Vertebrates > Mammals
5. Animals > Vertebrates > Reptiles
6. Animals > Invertebrates > Insects
7. Animals > Invertebrates > Others
9. Protoctists > Algae
10. Microscopic Organisms and Viruses
11. Human as a non-native species
Positive Effects of NNS
There are widespread indications of how introduced species have ameliorated the standard of living of humans throughout the historic ages, and propelled agricultural, social and even technological advancement of the human race. Without proliferating the domesticated food species that are transferred widely around the world to suitable regions for cultivation, the human population could not have risen exponentially, and as our population is still exploding the marginal drawbacks of this advancement is becoming increasingly alarming. In the historical times, wars would not have been fought in such a large scale if horses were not introduced through to Southern Asia and China from Europe; in the colonial ages of America, horses were introduced to North America and have since played large part in the daily life of people there as had been the case in Europe and beyond. Most ornamental plants found in temperate developed countries originated from tropical countries, and apart from bringing their beauty to close within reach, they can be sold for a fair price, and some are economically important crops, as are many cash crops, including rubber, as an example. Including Chrysanthemum, Tulips and Orchids, ornamentals are more or less controlled so that they cannot spread much away from where they are nurtured. Emancipated NNS are another matter.
Negavitve Effects of NNS
1. Ecological Impact
The single most important negative effect of NNS is their impact on the natural environment. It may not sound a great deal, but it is tantamount to leaving a daughter to a strange man's care. The capability of these introduced organisms does not seem to receive full appreciation even nowadays, and people keep shuffling the inhabitants of the world around at will, and sadly in many cases inadvertently, without taking heed of the damage they are inflicting upon the environment potentially.
Resources are limited, and bounteous as they look, natural resources are more limited in supply than you may think. To maximize the use of a resource, organisms have evolved special strategies. Different species usually have marginally discrepant niches if they are closely related, just like, say, your taking to chocolate milk, and your brother to strawberry-flavoured milk only, so that resources are neatly divided between species, and the productivity of an ecosystem is fully utilized. However if an elder brother takes both flavours at large plus skimmed milk, he is always well fed enough to compete with his brothers for the remaining milk. Generalist NNS either compete with the native species that share similar food sources, or explore other sources as well so that their numbers are sustained at higher levels, thus taking a larger percentage of resources available particular to the survival of some specialist natives, plunging the communities into a vicious cycle from which the native species could not easily liberate themselves in succumbing gradually to the NNS. Introduced trees and noxious weeds that threaten native vegetation crowd out other plants through growing leaves earlier in the season and many have a faster growth rate. That way the available light early in the season will be absorbed by the non-native species rather than the natives, and by the time the maximum growth period of the natives is reached the NNS have reached such a large size, with advanced foliage systems to catch sunlight, that the natives are outcompeted. In America as many as 500 exotic plants have managed to sustain themselves and a few have reached such population sizes that an area exceeding that of Texas is covered by introduced plants. And animals can be worse. Intricate food webs link the organisms dependent on green plants as food source to one another, and many animals cannot withstand large tracts of unfamiliar vegetations, which may not fill the ecological roles some native plants represent. Many fire ant species are unpalatable to Horned Lizards, which feed on native Ants that are displaced on a large scale by their vicious cousins. Species counting on the displaced natives for food perish as a result, and the cascade effect ensures that not just a single species is affected when the NNS directly competes with that species. Whole food webs can be disrupted by such invasions, and the supporting links of the ecosystem can be severed as a result, leading to ecosystem collapse.
Resources are much more than just nutrients. Birds must have a site for reproduction, and many American birds are hole-nesting species. Introduced birds may compete with them for nest sites and reduce breeding success in many native species. Air may be a luxury on land but in badly oxygenated water, any reduction to the oxygen level can spell disaster to native fish that may not be so tolerant of such an unprecedented environmental change. Introduced water weeds may reduce the oxygen level in water and threaten native fish in this way. Any NNS that knocks on the environment for more natural resources can threaten the neighbours' livelihood.
Direct predation falls squarely into this discussion. In an isolated environments such as islands and notably Australia, the modes of predation on the "mega" fauna is limited and native herbivorous Mammals and Birds are not prepared in any way for the radical changes brought about with the introduction of a single Cat, Fox, or several Rats that may not look anything more significant than being filthy and repulsive. They are repulsive to nesting songbirds, land birds and sea birds that lay their eggs conspicuously on the ground. Previously free of potent natural predators, many birds of the Pacific Islands and Hawaii have been eradicated by introduced Rats as they feed on adult and young birds alike. The last few centuries have witnessed just fewer than 70% of all terrestrial vertebrate species of Hawaii perish, and more than 90% of land birds endemic to Hawaii have embarked upon the pathway of extinction. The Po'ouli (Melamprosops phaeosoma), one of the thirty species of Hawaiian Honeycreepers that survived into the historical times, have only 3 existing individuals known and is following the footpaths of its relatives that had gone extinct over the last few centuries --- the main culprit are Pigs that uproot and degrade its understorey habitat on Maui, where once the understorey was lush and impenetrable. Mauritius has lost the Dodo back in the 15 th century to Rats, and many native birds are still highly endangered, as in many of the islands of the Western Indian Ocean. Australia have had many of their native Marsupials decimated from predation by Foxes, Cats, and competition for food with Rabbits; the latest, in particular, have drastically reduced the number of burrows available for small subterranean Marsupials such as Bilbies and Bandicoots. Foxes hunt medium-sized Marsupials such as Hare-wallabies and Rock Wallabies that cannot escape into burrows, and have significantly reduced their numbers. Up till now 19 of the small marsupials native to Australia have been wiped out mainly by the NNS. The Australian fauna is under siege, but the flora fares no better, as more than 10% of the plant species in Australia are NNS; this unique ecosystem is doing well not being vanquished at all, but many of the endemics would not have survived without conservation efforts. Guam and many of the South Pacific Islands have introduced Rats, and the former has had its whole endemic forest bird populations wiped out by a single species, the Brown Tree Snake. The Guam Broadbill (Myiagra freycineti) was one of the unique species that have evolved in Guam's tropical rainforests, and was lost around 1974 to snake predation. Numerous examples as such can be cited. Due to the fragile nature of island ecosystems, in which many small vertebrates have become accustomed to predator-free environments, and birds have turned to ground nesting or lost the defensive mechanism towards nest-raiders, any introduction of potential predators end up as ecological disasters.
2. Habitat Degradation
When a species has its population above astronomical levels, it is destined to have an effect on the outlook of the environment in which it lives, and the effect is most likely to be negative as a monopoly of the resources offered means that the necessary gradations and trophic levels to a healthy ecosystem are absent, and the original functioning of the ecosystem is bound to suffer disruptions and distortions. Noxious weeds can overgrow and turn healthy pastures into practical wastelands that are nevertheless not the required habitats for the natives; some water plants and Mollusks clog up waterways and canals, and make rivers and streams too cramped to accommodate certain fish species that require more open water, whilst water transport is also deterred. Algae overgrowing in favourable areas can foul fishnets and block water discharge chutes, damaging fisheries and creating unsightly patches along the shore, deterring wildlife and people all the same from using the area. Rabbits, Goats and Cattle are renowned for stripping pastures bare in places where the grass species are not hardy enough to stand such grazing pressure as what the large mammals presented, and Australian plains have progressed into a dust bowl of desert patches in addition to the extensive Great Victorian due to the NNS; the Big Island of Hawaii, much to its chagrin, have hosted goats and other grazing livestock that were relentless in feeding efforts, and many native plants are under the dual pressure from human clearance and overgrazing. The landscape is changed forever as the grass dies and the land turns derelict, not suitable for pastures and farmland alike as soil erosion drains away the nutrients needed for life and turns the land barren, with little recovery possible as long as the NNS persist. More direct effects of animals on the environment includes population explosions that infest cities and villages, such as the Cane Toad that grew completely out of control on the feast of defenseless native insects.
As a tolerably stable habitat is important for the survival for all organisms, radical changes to the basic physical conditions can be lethal to some of the more sensitive species. Often the ecosystem is traumatized from the bottom up, and the effect shows up most rapidly in the top predators as the number of preys available drops disproportionately more as we go up the energy pyramid. The top predators my then be called indicator species, meaning that their decline is indicative of underlying problems in the ecosystem that may not be apparent at first sight.
3. Economic Loss and Diseases
Figures speak for themselves. The United States suffer an economic loss of a minimal $137 million annually due to NNS. Within that $80 million are spent in dealing with noxious weeds and exotic plants that threaten the local ecosystems, which is 60% more than the annual income from agricultural exports, at around $50 million. In Australia, the agricultural damage caused by Rabbits alone amount to $20 million annually, and the controlling measures combined cost far more than this. It is estimated that pests eat almost 40% of all the crops grown worldwide, and amongst those pests many are NNS that have found no natural predators in the abnormal havens abound with food. They are allowed to multiple with the superb food source provided often by monoculture, which excludes all but the preferred food source of the pests --- care has been taken to remove weeds, pesticides have been sprayed to kill off large predators and deter any predators that may immigrate in search of food, but small insect pests do not have much difficulties escaping from the toxic substances by hiding in the foliage, and with the further reduction of enemies they are literally thrown into heaven, with unlimited food supply and no population control. Disastrous loss of crops is bound to ensue, and culprits include insects such as scale insects, aphids and other sap-feeding ones, and plant viruses that infect and kill large cash crop species such as the Banana Bunch Top Virus that attack banana trees.
Pathogenic outbreaks that have caused important socioeconomic mayhem are to a certain extent related to the non-native species problem. Many pathogens are themselves NNS, with viruses causing West Nile Fever, Hepatitis, Smallpox, Rabies, and other infamous diseases having been spread so thoroughly amongst the human population worldwide that infections occur quite frequently in places and outbreaks are not uncommon. Evidently a recent example of introduced viral pathogen is the Corona Virus causing the Severe Acute Respiratory Syndrome (SARS), which has clearly been demonstrated to have taken advantage of the air traffic and has been transported accidentally from Southern China, the original source of the outbreak, to remote places as Canada and other countries in the Oriental Region. In a similar way many of the less harmful viruses have already been spread as far as the human concentration stays above certain levels that the viral population is sustained. Viruses that affect wildlife are also encouraged with increasing pet trade and introduction of all sorts of NNS that may have been infected with the virus already. Bacteria are dispersed in the same way, and invariably these consist of more that have an effect on humans than on other animals in general, as the transport system approaches consummation within the bounds of prevalent technology. Bacteria that affect livestock are also commuted around the world where farms are situated, and losses from epidemics can be appreciated from the anthrax outbreaks earlier; food-and-mouth disease, caused by viruses, can kill hundreds of cattle in one go, and the approximate cost of vaccinating all the livestock may exceed $1 billion. In the outbreak in 1968 more than 430000 animals are slaughtered. Recent Avian Influenza outbreaks, which have spread from South-western China to Vietnam and beyond, have claimed the lives of tens of thousands of domestic fowl, and the supply of their meat is severely disrupted, and farmers have to bear the loss square in the head --- the estimates have yet to be publicized, but the effects are apparent.
NNS vectors have facilitated largely the killing spree of such diseases. Rats and Mosquitoes rank amongst the most efficient pathogen-transmitting organisms as many viruses and bacteria have life stages within these specific hosts, and their introduction has allowed the pathogens to roam free and wide. In the Hawaiian Islands, Mosquitoes have spread the Avian Malaria wherever they went and as native birds have zero resistance against this new disease whose efficiency in killing is astounding, epidemics have been maintained as one of the most important causes of decline of Hawaiian Birds. Malaria itself takes its toll on human circumtropically, and introduced Malaria Mosquitoes are keen distributors of this disease. The effect of novel pathogens can be extremely acute on humans that have never been brought into contact with the disease, but certain complications exist --- the idea holds, regardless, that NNS have caused huge threat to public health and the general well-being of wildlife as well.
The apparent difficulty in solving the NNS problem is that the relevant methods are hard to implement, and the targets are mostly too abundant to be effectively annihilated. However the successful examples of eradication are encouraging, and now the efforts of the governments, general public and individuals of many countries are determined to focus on combating NNS. Having also briefly introduced the practical methods of curbing the disaster of exotic species in their individual accounts, we will expand these solutions in detail through classifying the solutions into several main streams.
There are several aspects to this, namely removing the invaders directly, hunting the NNS or marketing them so that the general public has more incentive to assist in the removal of the species. Physical removal is slow and time-consuming, but it does not affect the natives we are trying to save negatively. There has been large-scale shooting of Rabbits in Australia, manual removal of the ubiquitous Pacific Sea Star from the South Australian Harbours by volunteers, and various traps designed for catching introduced Rats on the Pacific Islands, but none are extremely successful. Physical control can be useful in selectively harvesting introduced predatory fish, for example the Pike, Brown Trout, Largemouth Bass and those palatable, marketable species in order to keep their numbers down. In conjunction with other methods, physical control can be effective in the sense that the removal can be more thorough in special cases, but in most it can readily be apprehended that success is at any rate limited, as the manual clearing of overgrown weeds and Mikania vines exemplifies.
Pesticides, herbicides and poisons are quick and effective in killing off the NNS if applied properly. Important herbicides include glyphosate, Sonar, Weedar and Copper sulphate. They are rather easily applied to large and small areas alike, penetrate keep into the aquatic environment where it is frequently applied in places, and are inexpensive in many cases relative to other controls. The universal poisoning effect, however, affects not only the target organism but tends to kill all others in the path of the poison. When the plants are killed by herbicide, bacteria that initiate their decomposition use up a lot of oxygen in the water and the fish in the habitat can be killed as a result. Poison baits used to kill Mice, Foxes and Cats may be ingested by other terrestrial mammals; pesticides can kill off predatory arthropods that may otherwise have controlled the introduced pests better than the pesticide could accomplish. Poisonous substances can also leach away from the applied area and affect localities miles away, polluting the ecosystems around. These contaminate drinking water and sometimes affect human health, and it would not deviate much from the truth in saying that it is equivalent to chemical weapons that hit the wrong targets, leaving behind unsightly scars in the face of the environment. The last thing that the planet has not got enough of is the release of noxious chemicals that affect all life in its path without exemption.
Nature has the superb design that encompasses organisms in a certain area, and the rules are that they are intricately inter-dependent as in departments within a factory, which is why severing links do not allow the rest of the system to work terribly well. Biological controls are usually organisms known to feed or parasitize on a specific (range of) NNS, and as they are the natural predators of the target NNS, they purportedly do not feed on other native species we are striving to allow some breathing room for. The Cactus Moth from Argentina has been introduced in 1925 to control the Cactus Opuntia Stricta (see Species Accounts) and the success was unprecedented and inspiring, as the Prickly Pear numbers plummeted to virtual oblivion before a decade had passed. The Beetle Lebia grandis have saved the potato plantations in Southern United States as they have been discovered to be the indigenous natural predator of the Colorado Potato Beetle Leptinotarsa decemlineata, as the adult Lebia Beetle devours the larvae of the Potato Beetle quite happily when the former is introduced into infested zones.
Problems surface when we consider such species as the predatory Mite Euseius tularensis, which feeds on a variety of pests in Citrus tree plantations, such as Citrus Thrips, Scale Insects, Red Mites, as well as sap and pollen of the plants on a small extent. This generalist feeding behaviour does not ensure that its introduction will keep the numbers of the pests down, and the control may not be successful with this lack of specificity in the relationship between the non-native pests and the predator. However, if conditions that ensure optimum growth of the predator are achieved, it is not difficult for the parasitic wasp Eretmocerus eremicus to reduce introduced whitefly populations ( Trialeurodes sp. ) to extremely low levels, with the whitefly mortality within 8 weeks of application of the parasitic wasp as a biological control exceeding 98%. Given the susceptibility of the parasitic wasp, and many other species, to pesticides that in general are non-discriminatory between different insect species, it is inferred that chemical control is to a certain extent not compatible with biological control. When appropriately applied, biological controls are very effective and eco-friendly, provided that the predator is specific. Fiascos could take place as in the Cane Toad introduction to Australia to deal with Cane Beetles. Despite the titular similarity the Cane Toads are not confined to cane fields and have not been found to specialize on Cane Beetles, but they ate anything in their path as they spread from the plantations into the wild, raging all across Northern Australia. Applying biological control does require a lot of research before hand so that the biology, food preference, environmental requirements and tolerance are known and provided for in schemes that involve the use of their natural aptitude.
Other strategies that have been employed in terms of biological methods include the release of sterile males of a NNS that are expected to mate freely with the females of the introduced populations, causing sterility in the offspring they produce and thus interfering with the continuity of the species in its introduced range. This method has been quite effective, but is limited by the reproductive biology of the NNS under concern. Some plants reproduce largely vegetatively and it is conceivable that this strategy is not applicable.
Prevention and Quarantine
Pre-emptive measures, as the problem is ubiquitous nowadays and remedies have proved demoralizing, are enacted widely across the globe. Quarantine is useful for preventing a wide range of accidental introductions through the gateways and ports, and some deadly viruses such as the West Nile and anthrax have been found during routine immigration checking. Imports of livestock that may carry microorganisms that can cause an epidemic outbreak in the farms are in many places restricted and strictly quarantined. The invasion history of many NNS and their subsequent impact have shown to us how important it is to take all necessary precautions in thwarting the initial entry efforts, and stowaways such as the Brown Tree Snake, other possibly invasive Serpents, Rats, various types of insects that could rapidly establish themselves as agricultural pests, and perhaps the planktonic larvae of some invasive marine organisms contained in the ballast water of trans-oceanic vessels should be quarantined as appropriate in the future.
The applicability of quarantine varies a lot from different target organisms, as many NNS are difficult to pick out while others may readily succumb to such efforts. Nevertheless it is of the utmost importance that the screening is strictly carried out in order to minimize the chance of such a problem occurring over and over again. The cost-effectiveness of this approach simplifies a lot of subsequent hubbub about relevant measures, as the NNS is not established in the first place. Early detection of the invasion allows the related bodies to react quickly and annihilate the NNS whilst the scale of introduction is small enough that complete removal has not become impossible as in many documented cases.
Education and Government Regulations
What many conservation groups are doing at present is trying to make the public aware of the most pressing problems that are occurring to the fundamental entity we are all dependent on --- the environment that we live in. To a great extent, what it is defines what we are and what we could and could not do. A deprived, lifeless environment is depressing to the mind; the presence of wildlife strikes a chord within us, though the level of harmony varies. It must be realized after all though, that our lives are strictly dependent on environmental health. We have seen the effects of NNS on our environments and that we have caused it as a species implicates our obligation in trying to rectify the problem. Education about the non-native species problems is the expansion of this concept, the promotion of an awareness of the need to be pragmatic but contrite towards the issues related to the whimsical displacement of natural organisms with respect to their surroundings, and why this is so with a final word about how the situation could be reversed.
The solution of this problem relies on the joint effort of the government and people. In 2003 as many as 20 Acts about the tackling of NNS has been raised in the American Congress, and many of these regulations aim at reduction, prevention, and assistance towards the recovery of the affected ecosystems, notably the Great Lakes, the Hawaiian Islands and Florida. Worldwide, NNS hotspots include Australia and the surrounding islands, the Pacific Islands, South Africa, and parts of China. Most of these Acts raise awareness towards the NNS problem and initiate the flow of funds towards measures that help to alleviate the currently observed effects. Improved funding can be a great help to research on NNS that allows more of the biology of these successful species to be learnt and investigated, and databases of these species to be created in facilitation of public reference and for subsequent efforts to have a sound scientific support.
Wise management of the Environment
Humans are the stewards of the world, so says the Bible. Many people have not realized how much wisdom is contained in these lines. The integrity and health of an ecosystem, as that of a healthy body, can resist attack on its own. It is the debilitated ecosystems that are now unfortunately all over the world under the continued harassment of the human race --- overexploited ones, that are susceptible to introduced species, not to mention the isolated, fragile ones. What humans can do instead of adding to the planet's plight is to manage the environment wisely and sustainably. Restoration of the original environment after invasions have occurred will reinforce the native species and ensure that they have a firm grip on the natural resources, leaving little for the NNS to seize --- indeed studies have shown that intact ecosystems are less prone to invasion than those from which certain ecologically important species have been lost.
The fate of the planet is literally in human hands. It cannot be conjectured whether the NNS problem will be solved within our lifetime, but we hope that you have enjoyed using this site and have learnt much from the information.
# Test your knowledge~
# Click here to download the questions.
# Click here to download the answers
# Our Site
This is a team of the cream of the crop, no less in the eyes of the colleagues than in ours as advocators.
How the three teammates consummated their acquaintance would be too much to be portrayed in several lines, but they will be introduced to you. Ivan is a painter; his designs have an air of elegance and mystery about them, and he, on top of all, is keenly aware of the changing natural environment, portraying this phenomenon in several of his works that have been circulating amongst the students. Koel is a birdwatcher, and is basically enraptured when he hears of the topic, holding that this is a good opportunity for a knowledge boost about this worrying global crisis. Tony is a meticulous expert on computers and is positive that applying the joint knowledge to form an educational website would be one of the best ways to solve the practical problems, as the whimsical introduction of organisms to foreign areas can be regarded as an ill-informed, ignorant decision. With their skills, interest and foresight they make a concrete team that has produced a website to which the word satisfactory could not yet apply satisfactorily.
We hope you enjoy the website, whilst learning more about the topic, which is worth all the concern.
School: Abingdon School, Oxfordshire, UK
Hometown: Hong Kong
Hobbies: Playing badminton, painting, chatting on the phone
Ivan designed the frame of the website and the frontpage. He also helped making up some questions for the Test your Knowledge~ section, and contributed much to the layout and aesthetics of our website.
School: Abingdon School, Oxfordshire, UK
Hometown: Hong Kong
Hobbies: Birdwatching, playing piano, reading
Koel is the researcher and the content manager. He did most of the research and wrote most of the content in the website. He also made up most of the questions for the Test your Knowledge~ section.
School: Abingdon School, Oxfordshire, UK
Hometown: Hong Kong
Hobbies: Computer programming, playing piano, playing table-tennis
Tony is the web editor. He did all the technical bit in the website, incorporating and transforming all the information and designs into the webpages. He also programmed the search engine and made the game program for the Test your Knowledge~ section.
We would like to pay special thanks to our coach, Mr. Forster, who is our personal tutor at school. His inspiring guidance throughout the whole process of the website production strengthened our confidence and was very important in maintaining the team spirit. He constantly checked our progress in our meetings and most importantly reminded us of the deadline of the competition so that we could finish it on time!
# Links and References (Information and Photos Resources)
Australian Museum Online
|3.||Animal Diversity Web
|5.||Earth Crash Earth Spirit
|6.||US Geological Survey
|10.||The University of York
|13.||Fort Collins Science Centre Online
|14.||Non-Native Aquatic Species in Gulf of Mexico Region
|15.||Union of Concerned Scientists
|16.||Patuxent Wildlife Research Centre
|17.||Pacific Island Ecosystems Research Centre
|18.||College of Agricultural Sciences
|19.||Communications for a Sustainable Future
|20.||Student Ambassador Program
|21.||Natural Science Research Laboratory
|23.||Nonindigenous Aquatic Species
|24.||Cornell Lab of Ornithology
|26.||Australian Government Department of the Environment and Heritage
|27.||Gulf of Maine Aquarium Educate Concene Research Build
|29.||California Academy of Sciences
|31.||U.S. Environmental Protection Agency
|34.||University of Minnesota Department of Horticultural Science
|35.||National Council for Science and the Environment
|36.||College of Agriculture & Life Sciences
|37.||Emagazine.com The Environmental Magazine
|38.||Western Kentucky University
National Parks Conservation Association
Invasive species threaten national forests
Minnesota Department of Natural Resources
Ashland Fishery Resources office
Ecology of the Santa Margarita River - Non-native species
A State of the Nation's Ecosystem
Photo showing cowbird parasitism
Photo of Brown-headed Cowbird by Stephen O. Muskie
Photo of Brown Rat
Fish of the Great Lakes - Northern Pike
Zebra Mussel Information
Department of Fisheries - Introduced Marine Aquatic Invaders - North Pacific Sea Star
Environmental News Network - Cactus Moth eating its way South
Africanized Honey Bee best profile
Asian Longhorn Beetle
Pest Alert: Asian Longhorn Beetle
On Asian Longhorn Beetle eradication efforts
Columbia University in the City of New York
Information on Water Hyacinth
Invasive Non-indigenous Plants in Florida
Wisconsin Department of natural resources
Article on European Buckthorn
Caulerpa taxifolia factsheet
Green Algae of the family Caulerpaceae
Noxious Wildland Weeds of California
Prickly Pear invasion history (http://www.northwestweeds.nsw.gov.au/prickly_pear_history.htm)
Photo of Mozambique Tilapia
Photo of Nile Perch
College of veterinary medicine
|71.||Information Systems for Biotechnology
Control of Invasive Species
|73.||Image search on Google