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72-530: Increasing snow melt from the Rwenzoris, overgrazing , and other alterations to the watershed have caused bank erosion and frequent changes to the course of the meandering lower reaches of the river. In some places, Uganda is losing up to 10 metres (33 ft) of land per year on its side of the river to erosion and silt from the Semliki is gradually filling in the southern end of Lake Albert. In other places, it

144-415: A planetary body after the former is introduced by a space probe or spacecraft , either deliberately or unintentionally. It has also been hypothesized that the origin of life on earth is due to introductions of life from other planets billions of years ago, possibly by a sentient race. Projects have been proposed to introduce life to other lifeless but habitable planets in other star systems some time in

216-559: A 70-year period, identifying overgrazing, global changes, and the ecological effects of megafauna extinction as key factors. Their findings shed light on the multifaceted drivers behind changes in savannah ecosystems. Echoing this theme of alternative strategies to combat overgrazing, Kriegisch et al. (2019) demonstrated how drift- kelp availability could reduce the foraging movement of overgrazing sea urchins, suggesting that alternative food sources may significantly influence grazing behaviors and aid in managing marine ecosystem pressures. In

288-830: A native of East Asia, has been introduced into parts of Europe for ornamental reasons. Many plants have been introduced with the intent of aesthetically improving public recreation areas or private properties. The introduced Norway maple for example occupies a prominent status in many of Canada's parks. The transport of ornamental plants for landscaping use has and continues to be a source of many introductions. Some of these species have escaped horticultural control and become invasive. Notable examples include water hyacinth , salt cedar , and purple loosestrife . In other cases, species have been translocated for reasons of "cultural nostalgia", which refers to instances in which humans who have migrated to new regions have intentionally brought with them familiar organisms. Famous examples include

360-437: A new region may escape from captive or cultivated populations and subsequently establish independent breeding populations. Escaped organisms are included in this category because their initial transport to a new region is human motivated. The widespread phenomena of intentional introduction has also been described as biological globalization . Positive Introductions Although most introduced species have negative impacts on

432-584: A novel environment (e.g.: in Europe , house sparrows are well established since early Iron Age though they originated from Asia ). Immigrant species are species that travel, sometimes by themselves, but often with human help, between two habitats. Invasiveness is not a requirement. Introduction of a species outside its native range is all that is required to be qualified as an "introduced species". Such species might be termed naturalized , "established", or "wild non-native species". If they further spread beyond

504-463: A parasite or herbivore with it. Some become invasive, for example, the oleander aphid , accidentally introduced with the ornamental plant, oleander . Yet another unintentional pathway of introduction is during the delivery of humanitarian aid in the aftermath of natural disasters. This occurred during relief efforts for Hurricane Maria in Dominica , it was found that the common green iguana ,

576-467: A population decrease. This was seen in the Atlantic Salmon population when high levels of escape from Atlantic Salmon farms into the wild populations resulted in hybrids that had reduced survival. Potential positive effects include adding to the genetic diversity of the population which can increase the adaptation ability of the population and increase the number of healthy individuals within

648-758: A population. This was seen in the introduction of guppies in Trinidad to encourage population growth and introduce new alleles into the population. The results of this introduction included increased levels of heterozygosity and a larger population size . Wide-spread introductions of non-native iguanas are causing devastating effects on native Iguana populations in the Caribbean Lesser Antilles , as hybrids appear to have higher fitness than native iguanas, leading to competitive outcompetition and replacement. Numerous populations have already become extinct and hybridization continues to reduce

720-470: A similar vein, the research by Cai et al. (2020) presents a stark example of the terrestrial impact of overgrazing, showing how the fertile island effect collapses under extreme conditions in shrub-encroached grasslands . This case study emphasizes the critical need for sustainable grazing practices to protect soil health and maintain ecosystem functionality, further illustrating the wide-reaching consequences of overgrazing across diverse habitats. Overgrazing

792-449: A species is considered "introduced" when its transport into an area outside of its native range is human mediated. Introductions by humans can be described as either intentional or accidental. Intentional introductions have been motivated by individuals or groups who either (1) believe that the newly introduced species will be in some way beneficial to humans in its new location or, (2) species are introduced intentionally but with no regard to

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864-458: Is a massive threat to the native species of flora and fauna, especially the native bushes which are often overlooked by invasive species looking for homes. Mustalids, rabbits, hares and possums often eat the plants that hold soil together. This makes the ground very unstable and crumbly. If soil is unstable, it is prone to collapse in extreme weather events such as floods and heavy rain. This is detrimental to farmers of crops and animals alike. 40% of

936-507: Is considered the main cause of woody plant encroachment at the expenses of grasses on a land area of up to 45 million hectares. In many arid zones in Australia , overgrazing by sheep and cattle during the 19th century, as pastoralism was introduced by European settlers, caused many long-lived species of trees and shrubs to give way to short-lived annual plants and weed species. Introduced feral rabbits , cats and foxes exacerbated

1008-528: Is highly variable. Some have a substantial negative effect on a local ecosystem (in which case they are also classified more specifically as an invasive species ), while other introduced species may have little or no negative impact (no invasiveness), and integrate well into the ecosystem they have been introduced to. Some species have been introduced intentionally to combat pests. They are called biocontrols and may be regarded as beneficial as an alternative to pesticides in agriculture for example. In some instances

1080-488: Is likely to cause economic or environmental harm or harm to human health". The biological definition of invasive species, on the other hand, makes no reference to the harm they may cause, only to the fact that they spread beyond the area of original introduction. Some argue that "invasive" is a loaded word and harm is difficult to define. From a regulatory perspective, it is neither desirable nor practical to list as undesirable or outright ban all non-native species (although

1152-493: Is seldom understood in the beginning, and many non-native ornamentals languish in the trade for years before suddenly naturalizing and becoming invasive. Studies have shown that introduced species display a greater likeliness of naturalizing when there is an appropriate environmental match, the plant species are short lived herbs or cultivate from seeds. Peaches , for example, originated in China, and have been carried to much of

1224-575: Is the European rabbit in Australia . Thomas Austin , a British landowner, had rabbits released on his estate in Victoria because he missed hunting them. A more recent example is the introduction of the common wall lizard ( Podarcis muralis) to North America by a Cincinnati boy, George Rau, around 1950 after a family vacation to Italy . Intentional introductions have also been undertaken with

1296-593: Is the seaweed Caulerpa taxifolia . Caulerpa was first observed in the Mediterranean Sea in 1984, off the coast of Monaco . By 1997, it had covered some 50 km . It has a strong potential to overgrow natural biotopes , and represents a major risk for sublittoral ecosystems . The origin of the alga in the Mediterranean was thought to be either as a migration through the Suez Canal from

1368-458: Is the DRC that is losing territory as the changing river course alters the apparent location of the border. The Semliki begins near Ishango , DRC, at the northern end of Lake Edward and soon enters Virunga National Park , through which it flows over much of its upper course. The A-109 road between Mpondwe , Uganda, and Beni , DRC, is on the right , sometimes nearby and sometimes at a distance, as

1440-859: Is the reintroduction of a species that has become locally endangered or extinct, done in the interests of conservation. Examples of successful reintroductions include wolves to Yellowstone National Park in the U.S., and the red kite to parts of England and Scotland. Introductions or translocations of species have also been proposed in the interest of genetic conservation , which advocates the introduction of new individuals into genetically depauperate populations of endangered or threatened species. Unintentional introductions occur when species are transported by human vectors. Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native. For example, three species of rat (the black, Norway and Polynesian) have spread to most of

1512-551: Is the small Indian mongoose ( Urva auropunctata ). Originating in a region encompassing Iran and India , it was introduced to the West Indies and Hawaii in the late 1800s for pest control. Since then, it has thrived on prey unequipped to deal with its speed, nearly leading to the local extinction of a variety of species. In some cases, introduced animals may unintentionally promote the cause of rewilding . For example, escaped horses and donkeys that have gone feral in

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1584-645: Is used as an example in the economic concept now known as the Tragedy of the Commons devised in a 1968 paper by Garrett Hardin . This cited the work of a Victorian economist who used as an example the over-grazing of common land. Hardin's example could only apply to unregulated use of land regarded as a common resource. Normally, rights of use of common land in England and Wales were, and still are, closely regulated, and available only to "commoners". If excessive use

1656-594: The American bison and the turkey are non-native species to North America. Collectively, non-native crops and livestock account for 98% of US food. These and other benefits from non-natives are so vast that, according to the Congressional Research Service, they probably exceed the costs. Other examples of species introduced for the purposes of benefiting agriculture , aquaculture or other economic activities are widespread. Eurasian carp

1728-536: The American bison of the Great Plains , or migratory wildebeest of the African savannas , or by holistic planned grazing. Overgrazing typically increases soil erosion . With continued overutilization of land for grazing, there is an increase in degradation. This leads to poor soil conditions that only xeric and early successional species can tolerate. A meta-analysis of 148 studies found that

1800-684: The Australian Dung Beetle Project in an effort to reduce the impact of livestock manure. The timber industry promoted the introduction of Monterey pine ( Pinus radiata ) from California to Australia and New Zealand as a commercial timber crop. These examples represent only a small subsample of species that have been moved by humans for economic interests. The rise in the use of genetically modified organisms has added another potential economic advantage to introducing new/modified species into different environments. Companies such as Monsanto that earn much of their profit through

1872-553: The Cuban tree frog , and potentially the Venezuela snouted tree frog were introduced with the former two becoming established. Most accidentally or intentionally introduced species do not become invasive as the ones mentioned above. For instance, Some 179 coccinellid species have been introduced to the U.S. and Canada; about 27 of these non-native species have become established, and only a handful can be considered invasive, including

1944-481: The Nile ). Overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves , or nature reserves . It can also be caused by immobile, travel restricted populations of native or non-native wild animals . Overgrazing reduces

2016-560: The State of Hawaii has adopted an approach that comes close to this). Regulations require a definitional distinction between non-natives that are deemed especially onerous and all others. Introduced "pest" species, that are officially listed as invasive, best fit the definition of an invasive species. Early detection and rapid response is the most effective strategy for regulating a pest species and reducing economic and environmental impacts of an introduction. Management of invasion pathways are on

2088-524: The cane toad and red fox in Australia , nutria in North America , Eurasia , and Africa , and the common brushtail possum in New Zealand . In Taiwan , the success of introduced bird species was related to their native range size and body size; larger species with larger native range sizes were found to have larger introduced range sizes. One notoriously devastating introduced species

2160-573: The Americas may play ecological roles similar to those of the equids that became extinct there at the end of the Pleistocene . The exotic pet trade has also been a large source of introduced species. The species favored as pets have more general habitat requirements and larger distributions. Therefore, as these pets escape or are released, unintentionally or intentionally, they are more likely to survive and establish non-native populations in

2232-697: The Indian subcontinent and is impacting a range of wild species including urban birds. Most introduced species do not become invasive. Examples of introduced animals that have become invasive include the gypsy moth in eastern North America , the zebra mussel and alewife in the Great Lakes , the Canada goose and gray squirrel in Europe, the beaver in Tierra del Fuego , the muskrat in Europe and Asia ,

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2304-433: The Mediterranean region, where it can form monocultures that threaten critical conservation habitats. Japanese knotweed grows profusely in many nations. Human beings introduced it into many places in the 19th century. It is a source of resveratrol , a dietary supplement. It can grow in building foundations, threatening their stability, and spreads quite quickly. Mesquite ( Prosopis juliflora ) has spread very widely across

2376-575: The Mongolian steppes, Liu et al. (2013) found that approximately 60% of vegetation decline could be attributed to climate factors, with the rest significantly influenced by increased goat density due to overgrazing. This points to a complex interplay between climate change and grazing practices in ecosystem degradation. Further expanding our understanding, Stevens et al. (2016) investigated woody encroachment in South African savannahs over

2448-681: The Red Sea, or as an accidental introduction from an aquarium. Another troublesome plant species is the terrestrial plant Phyla canescens , which was intentionally introduced into many countries in North America, Europe, and Africa as an ornamental plant. This species has become invasive in Australia, where it threatens native rare plants and causes erosion and soil slumping around river banks. It has also become invasive in France where it has been listed as an invasive plant species of concern in

2520-624: The Uganda town of Bundibugyo . Downstream of the road crossing, the river leaves the Virunga Park and runs along the west edge of Semuliki National Park , which is in Uganda. Here the river becomes the border between the DRC and Uganda, and it remains the border for most of the rest of the river's course. As the river leaves Semuliki Park, it nears Sempaya National Park and the Toro Game Reserve , both in Uganda. Over its last reach,

2592-436: The aim of ameliorating environmental problems. A number of fast spreading plants such as kudzu have been introduced as a means of erosion control. Other species have been introduced as biological control agents to control invasive species . This involves the purposeful introduction of a natural enemy of the target species with the intention of reducing its numbers or controlling its spread. A special case of introduction

2664-405: The biodiversity. Turning to the aquatic environment, Ling et al. (2015) have documented the phenomenon of catastrophic sea urchin overgrazing and its role in marine ecosystem regime shifts. Their study underscores the urgent need for effective management and conservation strategies to mitigate the profound ecological impacts of overgrazing, highlighting the issue's global scope. Similarly, on

2736-532: The broadest and most widely used sense, an introduced species is synonymous with "non-native" and therefore applies as well to most garden and farm organisms; these adequately fit the basic definition given above. However, some sources add to that basic definition "and are now reproducing in the wild", which means that species growing in a garden, farm, or house may not meet the criteria unless they escape and persist. There are many terms associated with introduced species that represent subsets of introduced species, and

2808-539: The economy. There have been calls from scientists to consider a species "invasive" only in terms of their spread and reproduction rather than the harm they may cause. According to a practical definition, an invasive species is one that has been introduced and become a pest in its new location, spreading (invading) by natural means. The term is used to imply both a sense of urgency and actual or potential harm. For example, U.S. Executive Order 13112 (1999) defines "invasive species" as "an alien species whose introduction does or

2880-585: The ecosystems they enter into, there are still some species that have affected the ecosystem in a positive way. For example, in New Hampshire invasive plants can provide some benefits to some species. Invasive species such as autumn olive, oriental bittersweet, and honeysuckle produce fruit that is used by a handful of fruit-eating bird species. The invasive plants can also be a source of pollen and nectar for many insects, such as bees. These invasive plants were able to help their ecosystem thriving, and increase

2952-473: The forefront of eliminating unwanted invasive species this would include preliminary steps; educating the public, cooperation from industries and government resources. In Great Britain , the Wildlife and Countryside Act 1981 prevents the introduction of any animal not naturally occurring in the wild or any of a list of both animals or plants introduced previously and proved to be invasive. By definition ,

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3024-586: The intentionally introduced Harmonia axyridis , multicolored Asian lady beetle . However the small percentage of introduced species that become invasive can produce profound ecological changes. In North America, Harmonia axyridis has become the most abundant lady beetle and probably accounts for more observations than all the native lady beetles put together. Many non-native plants have been introduced into new territories, initially as either ornamental plants or for erosion control, stock feed, or forestry. Whether an exotic will become an invasive species

3096-849: The introduction of common starlings to North America by the American Eugene Schieffelin , a lover of the works of Shakespeare and the chairman of the American Acclimatization Society , who, it is rumoured, wanted to introduce all of the birds mentioned in Shakespeare's plays into the United States. He deliberately released eighty starlings into Central Park in New York City in 1890, and another forty in 1891. Yet another prominent example of an introduced species that became invasive

3168-489: The invasive comb jelly Mnemiopsis leidyi , the dangerous bacterium Vibrio cholerae , or the fouling zebra mussel . The Mediterranean and Black Seas, with their high volume shipping from exotic sources, are most impacted by this problem. Busy harbors are all potential hotspots as well: over 200 species have been introduced to the San Francisco Bay in this manner making it the most heavily invaded estuary in

3240-680: The local ecosystem. Introduced species that become established and spread beyond the place of introduction are considered naturalized . The process of human-caused introduction is distinguished from biological colonization , in which species spread to new areas through "natural" (non-human) means such as storms and rafting . The Latin expression neobiota captures the characteristic that these species are new biota to their environment in terms of established biological network (e.g. food web ) relationships. Neobiota can further be divided into neozoa (also: neozoons, sing. neozoon, i.e. animals) and neophyta (plants). The impact of introduced species

3312-547: The native animal's chances of survival. Several introduced exotic trees served as nest sites for resident waterbird species in Udaipur city, India. Perhaps the most common motivation for introducing a species into a new place is that of economic gain. Non-native species can become such a common part of an environment, culture, and even diet that little thought is given to their geographic origin. For example, soybeans , kiwi fruit , wheat , honey bees , and all livestock except

3384-510: The native species of New Zealand have been wiped out by pests including humans. Introduced species An introduced species , alien species , exotic species , adventive species , immigrant species , foreign species , non-indigenous species , or non-native species is a species living outside its native distributional range , but which has arrived there by human activity, directly or indirectly, and either deliberately or accidentally. Non-native species can have various effects on

3456-459: The new environment. Adventive species are often considered synonymous with "introduced species", but this term is sometimes applied exclusively to introduced species that are not permanently established. Naturalized species are often introduced species that do not need human help to reproduce and maintain their population in an area outside their native range (no longer adventive), but that also applies to populations migrating and establishing in

3528-517: The number of native iguanas on multiple islands. In plants, introduced species have been observed to undergo rapid evolutionary change to adapt to their new environments, with changes in plant height, size, leaf shape, dispersal ability, reproductive output, vegetative reproduction ability, level of dependence on the mycorrhizal network , and level of phenotype plasticity appearing on timescales of decades to centuries. It has been hypothesized that invasive species of microbial life could contaminate

3600-506: The park, as do over 490 species of butterflies. Among the mammals in the park are elephants, leopard , African golden cat , buffalo, hippopotami , duikers , and pygmy scaly-tailed flying squirrels . Along its course, the Semliki falls about 300 m (1,000 ft) through a series of rapids, and this isolates Lake Edward 's fish species, many of them found no-where else, from those found downriver in Lake Albert (and consequently

3672-431: The place of introduction and cause damage to nearby species, they are called " invasive species ". The transition from introduction, to establishment and to invasion has been described in the context of plants. Introduced species are essentially "non-native" species. Invasive species are those introduced species that spread widely or quickly and cause harm, be that to the environment, human health, other valued resources, or

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3744-778: The populated world. Tomatoes are native to the Andes . Squash ( pumpkins ), maize (corn), and tobacco are native to the Americas , but were introduced to the Old World . Many introduced species require continued human intervention to survive in the new environment. Others may become feral, but do not seriously compete with natives, but simply increase the biodiversity of the area. One example would be Dandelions in North America , which have become an essential source of early season nectar for both native and introduced pollinators, and do not meaningfully compete with native grasses or flowers. A very troublesome marine species in southern Europe

3816-572: The potential for being beneficial or detrimental in the long run remains unknown. The effects of introduced species on natural environments have gained much scrutiny from scientists, governments, farmers and others. The formal definition of an introduced species from the United States Environmental Protection Agency is "A species that has been intentionally or inadvertently brought into a region or area. Also called an exotic or non-native species". In

3888-436: The potential impact. Unintentional or accidental introductions are most often a byproduct of human movements and are thus unbound to human motivations. Subsequent range expansion of introduced species may or may not involve human activity. Species that humans intentionally transport to new regions can subsequently become successfully established in two ways. In the first case, organisms are purposely released for establishment in

3960-464: The purposes of sport fishing and hunting. The introduced amphibian ( Ambystoma tigrinum ) that threatens the endemic California salamander ( A. californiense ) was introduced to California as a source of bait for fishermen. Pet animals have also been frequently transported into new areas by humans, and their escapes have resulted in several introductions, such as feral cats , parrots , and pond slider . Lophura nycthemera ( silver pheasant ),

4032-634: The river flows west of the international border and enters the southern end of Lake Albert at a point southeast of Bunia , DRC. The two main ethnic groups in the region are the Amba people (Baamba, Bwamba) and the Bakonjo (Konjo). People in the Semliki Valley include Batuku, pastoral cattle keepers whose herds graze on grasslands along the river. Small populations of Batwa (pygmies), who have traditionally been forest hunter-gatherers , also live in

4104-605: The river meanders through the park. Slightly southeast of Beni, the river passes under the A-109 road and continues north. At this point, the stream is west of Mount Baker (Kiyanja) in Rwenzori Mountains National Park in Uganda. Before leaving the park, the river passes under another road linking the DRC settlement of Oicha to settlements in the Semliki Valley west of the DRC–;Uganda border and

4176-519: The selling of genetically modified seeds has added to the controversy surrounding introduced species. The effect of genetically modified organisms varies from organism to organism and is still being researched today, however, the rise of genetically modified organisms has added complexity to the conversations surrounding introduced species. Introductions have also been important in supporting recreation activities or otherwise increasing human enjoyment. Numerous fish and game animals have been introduced for

4248-815: The surrounding land in Australia. In the Caribbean region, overgrazing is a threat to vegetation areas where there is livestock farming, which is an important source of livelihood and food security for many people. a combination of small scale livestock farming with small ruminants, and mixed farming is practised. However, livestock consume vegetation faster than it can be renewed and this leads to land degradation, loss of vegetative areas, and soil erosion resulting in poor quality feed and reduced livestock yields and income. Also, these grazing lands are critical in controlling carbon dioxide and mitigating risks against severe weather such as floods and droughts. Overgrazing weakens ecological conservation. In New Zealand , overgrazing

4320-628: The terminology associated with introduced species is now in flux for various reasons. Examples of these terms are "invasive", "acclimatized", "adventive", "naturalized", and "immigrant" species. The term "invasive" is used to describe introduced species that cause ecological, economic, or other damage to the area in which they were introduced. Acclimatized species are introduced species that have changed physically and/or behaviorally in order to adjust to their new environment. Acclimatized species are not necessarily optimally adjusted to their new environment and may just be physically/behaviorally sufficient for

4392-611: The threat to both flora and fauna . Many bird species have become extinct or endangered, and many of the medium-sized desert mammals are now completely extinct or only exist on a few islands of Australia . Overgrazing can also occur with native species. In the Australian Capital Territory , the local government in 2013 authorised a cull of 1455 kangaroos due to overgrazing. Maisie Carr (1912-1988), Ecologist and Botanist, undertook significant research and studies in overgrazing and established consequences on

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4464-693: The use of common land in England and Wales was a triumph of conserving a scarce resource using agreed custom and practice. There have been overgrazing consequences in the region Sahel region. The violent herder–farmer conflicts in Nigeria , Mali , Sudan and other countries in the Sahel region have been exacerbated by land degradation and overgrazing. See 2010 Sahel famine . Various countries in Sub-Sahara Africa are affected by overgrazing and resulting ecological effects. In Namibia , overgrazing

4536-442: The usefulness, productivity and biodiversity of the land and is one cause of desertification and erosion . Overgrazing is also seen as a cause of the spread of invasive species of non-native plants and of weeds . Degrading land, emissions from animal agriculture and reducing the biomass in a ecosystem contribute directly to climate change between grazing events. Successful planned grazing strategies have been in support of

4608-483: The valley. In Semuliki National Park, the forest resembles that of the Congo River basin. Cynometra alexandri , a tropical tree species, dominates but is interspersed with other trees and swamp flora. Annual rainfall in this tropical forest averages 1,500 millimetres (59 in). More than 400 bird species, including the forest ground-thrush , Sassi's olive greenbul , and nine species of hornbill frequent

4680-483: The value of most ecosystem functions declines with increasing grazing intensity and that increasing aridity weakens positive impacts of light grazing. Native plant grass species, both individual bunch grasses and in grasslands , are especially vulnerable. For example, excessive browsing by white-tailed deer can lead to the growth of less preferred species of grasses and ferns or non-native plant species that can potentially displace native, woody plants, decreasing

4752-619: The wild. Among the popular exotic pets that have become alien or invasive species are parrots, frogs, terrapins, and iguanas. Some species, such as the Western honey bee , brown rat , house sparrow , ring-necked pheasant , and European starling , have been introduced very widely. In addition there are some agricultural and pet species that frequently become feral ; these include rabbits , dogs , ducks , snakes , goats , fish , pigs , and cats . Many water fleas such as Daphnia , Bosmina and Bythotrephes have introduced around

4824-423: The wild. It is sometimes difficult to predict whether a species will become established upon release, and if not initially successful, humans have made repeated introductions to improve the probability that the species will survive and eventually reproduce in the wild. In these cases, it is clear that the introduction is directly facilitated by human desires. In the second case, species intentionally transported into

4896-427: The world as hitchhikers on ships, and arachnids such as scorpions and exotic spiders are sometimes transported to areas far beyond their native range by riding in shipments of tropical fruit. This was seen during the introduction of Steatoda nobilis (Noble false widow) worldwide through banana shipments. Further there are numerous examples of marine organisms being transported in ballast water , among them

4968-431: The world, causing dramatic changes in native freshwater ecosystems. When a new species is introduced, the species could potentially breed with members of native species, producing hybrids. The effect of the creating of hybrids can range from having little effect, a negative effect, to having devastating effects on native species. Potential negative effects include hybrids that are less fit for their environment resulting in

5040-603: The world. There is also the accidental release of the Africanized honey bees (AHB), known colloquially as "killer bees") or Africanized bee to Brazil in 1957 and the Asian carp to the United States. The insect commonly known as the brown marmorated stink bug ( Halyomorpha halys ) was introduced accidentally in Pennsylvania. Another form of unintentional introductions is when an intentionally introduced plant carries

5112-534: Was first introduced to the United States as a potential food source. The apple snail was released in Southeast Asia with the intent that it be used as a protein source, and subsequently to places like Hawaii to establish a food industry. In Alaska, foxes were introduced to many islands to create new populations for the fur trade. About twenty species of African and European dung beetles have established themselves in Australia after deliberate introduction by

5184-433: Was made of common land, for example in overgrazing, a common would be "stinted", that is, a limit would be put on the number of animals each commoner was allowed to graze. These regulations were responsive to demographic and economic pressure; thus rather than let a common become degraded, access was restricted even further. This important part of actual historic practice was absent from the economic model of Hardin. In reality

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