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• International trade and travel are believed to be the leading cause of harmful intentional introductions. • Most plant and vertebrate species introductions have been intentional for e. g. plants as ornamentals, mammals and birds as game, and fish for sport fishing. • Most invertebrates and microbe introductions have been accidental, often attached to other species introduced intentionally. • Agricultural weeds have often been introduced as contaminants or crop seeds.
DELIBERATE OR INTENTIONAL INTRODUCTIONS • Agriculture and forestry species • Plants for soil improvement and stabilisation • Ornamental plants • Hunting and sport (e. g. red deer in New Zealand, rainbow trout in Chile and New Zealand) • Food resources (birds, fish, mammals, crop plants – e. g. rabbit in Australia, pig in Hawaii) Gulley erosion caused by rabbits in Australia
DELIBERATE OR INTENTIONAL INTRODUCTIONS • Biological control (e. g. fox to control rabbits; giant toad to control cane beetles in Australia; mongoose to control rats in Hawaii) • Fishery releases • Pet trade • Fashion and aesthetics (e. g. songbirds in Hawaii, house sparrow and starling in North America and SA, and grey squirrel in Europe; possums for fur trade in New Zealand)
WHY INTRODUCE THESE SPECIES? – a closer look Comfort and familiarity (recreate “home”) Ignorance re use of native species Cultural and religious reasons Biological control and restoration Pets, sport, fashion, aesthetics Economic benefit Community upliftment (aid agencies) Most intentional introductions economic purposes (Mc. Neely, 1999). http: //www. midatlantic. net/8 x 10/ • • The general result of deliberate introductions has been termed the ‘Frankenstein Effect’ because so many well-intentioned introductions have had unexpected consequences, usually negative (Moyle and Light, 1996).
HORTICULTURE • Major pathway of invasive alien species introductions. • Horticulture includes not only species introduced for ornamental purposes, but also for agricultural, medicinal or aesthetic purposes, to botanical gardens, nurseries, culinary stores (herbs for cooking), pharmaceuticals (human and veterinarian medicines) and engineering companies (for land restoration, reclamation and stabilisation) (Reichard and White, 2001). http: //www. daylilyladies. com/ http: //www. garringer. net/foam/archives/images/NURSERY. gif
HORTICULTURE cont. • The Spanish were the first to introduce the peach to America. Later, apple, pear and cherry trees were introduced. • Other US examples include the Norway maple, Japanese barberry, English Ivy and Oriental bittersweet all of which have escaped from cultivation (Baskin, 2002; Harrington et al, 2003). http: //www. unc. edu/~pyzuo/teaching. html • Education is essential to controlling random import of species for cultivation (Harrington et al, 2003). The advantage of recognising this is that it is a potentially easy pathway to manage.
DELIBERATE FISH INTRODUCTIONS http: //www. pasarmalam. com. sg/~dragongate/images/photos/big-fish/nileperch 02 -l. jpg • In the 1950’s, colonial authorities began stocking Lake Victoria with the Nile perch. This has led to the disappearance of ± 200 native cichlid fish species (Lodge 2001). • Mosquito fish are still being released in some countries as biocontrol, even though it is an invasive alien and causes harm by predating on many indigenous species. It was initially introduced to reduce mosquito populations, and thought to consume large amounts of mosquito larvae, but discovered to be no more effective than native fish species.
POSSUMS http: //www. richard-seaman. com/Mammals/Australia/ Brush-tailed possums from Australia were introduced into New Zealand between 1858 and 1900 to establish a fur trade, but in New Zealand there were fewer competitors, predators and parasites than in Australia, so they have successfully spread and sometimes reached densities ten times that in Australia. These possums have caused considerable damage to native forests, through defoliation and elimination of preferred food plants (Mc. Neely, 1996).
PET TRADE The pet trade often introduces exotic species into novel areas. Many of these species can be selected and bought from catalogues over the internet. Many of these species are difficult to care for or simply can’t exist in these new areas, and are set free into the wild (some may escape) when people no longer can or want to care for them.
ROSE-RINGED PARAKEET The rose-ringed parakeet was introduced into Cape Town in the 1850 s as a caged bird. The feral population started after accidental escape or possibly liberated aviary birds. There are feral populations in many parts of the world and in SA they currently exist in Kwa. Zulu-Natal and Johannesburg. With increased introductions and increasing numbers, it can become a serious threat to crops and indigenous hole-nesting birds (Dean, 2000).
ACCIDENTAL INTRODUCTIONS FROM INITIALLY INTENTIONAL INTRODUCTIONS INTO CAPTIVITY • • Escaped species from zoos and botanical gardens Farmed animals and pet trade Aquaculture and mariculture Research
ACCIDENTAL INTRODUCTIONS • Contaminants of agricultural produce (seeds, plants, fruit and vegetables, wood, soil) • Soil-inhabitants • Species hidden on machinery, equipment, vehicles • Hitch-hikers in package material, cargo, mail, planes • Ballast soil and sediments • Ballast water and hull fouling • Debris • Tourists and their luggage or equipment • Diseases in animals traded for other purposes • Parasites, pathogens and hitch-hikers of agriculture & mariculture http: //www. soultravel. nu/2003/ 031010 -celebs-NDU/index. asp • Whereas purposeful introductions might be controlled by legislation or regulation, accidents may be far more important in the spread of introduced species and much more difficult to control (Mc. Neely, 1999).
VECTORS OF SPREAD AFTER INTRODUCTION • Spread from neighbouring countries • Human-made structures which enhance the spread of alien species (inter-basin transfers, canals) • Human alteration of habitats and changed in agricultural practices • Some species introductions have been facilitated by human activities, but have traveled under their own power to new areas. http: //www. photoatlas. com/pics 02/pictures_of_panama_74. html
VECTORS OF SPREAD AFTER INTRODUCTION cont. • Some have taken advantage of man-made corridors to cross previously impenetrable barriers. E. g. Sea lamprey was able to invade the upper Great Lakes where it decimated native populations of lake trout and white fish, after construction of the Welland Canal enabled it to bypass the Niagara Falls. • Similarly the Suez Canal has enabled the introduction of at least 30 fish species into the Mediterranean Sea from the Red Sea. • Clearing of forest and introduction of domestic livestock has enabled the cattle egret to colonize South America from Africa.
Chapter 1 Definitions Chapter 2 History, globalisation and GMOs Chapter 3 The human dimension Chapter 4 Pathways of introduction Next Chapter 5 Characteristics of invasive alien species Chapter 6 The ecology of biological invasions Chapter 7 Impacts of invasive alien species Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 I hope that you found chapter 4 informative and that you will enjoy chapter five!