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AQUATIC ECOSYSTEMS • The integrity of aquatic ecosystems is being challenged worldwide by invading species. • Affected aquatic ecosystems include estuaries, fresh water, marine and wetlands. • Species are introduced by means of ballast water, hull fouling, infrastructure (canals), aquaculture and many other pathways. http: //www. cajunimages. com/free%20 downloads %20 page%202. htm
FRESHWATER • Some examples include the Nile perch, sea lamprey, zebra mussel and brown trout. http: //www. solarexpert. com/fishing/catch-n -release 2. html • Tolerant of a wide range of environments, the brown trout continues to be stocked for recreational fisheries in rivers and streams in the USA. The species reproduces well, and predates or competes with many indigenous fish and amphibian species.
MARINE A significant invasive in Europe is Leidy’s comb jelly (Mnemiopsis leidyi). It was probably released from ballast waters. It feeds on zooplankton, and since there were no predators in the Black Sea, food webs were damaged, leading to the collapse of anchovy and other fisheries – a significant ecological as well as economic impact. http: //www. lksd. org/kongiganak/Continuous. Ed. Ca rnagie/Carnagie/Earth. Science/Ocean/Earth. Ch 5 Ocean 4. htm
BALLAST WATER • The US receives more than 79 million tons of ballast water from overseas each year. Ballast tanks carry a diverse community of organisms, resulting in many biological invasions. Pathogens are common in coastal waters and can also be transferred in ballast water (Ruiz et al, 2000). • Ballast water is surprisingly not the most significant pathway of IAS introduction for the US. Stocking and aquarium release are the most significant pathways for fishes, with baitfish and food importation close behind. Ballast water treatment technologies include: Ozonation treatment UV Irradiation Natural Product Biocide Deoxygenation
HULL FOULING • Barnacles, mussels, sponges, algae, sea squirts etc. attach themselves to the hulls of ships, fouling them. • Invasions can occur when these fouling organisms come in contact with structures in a new port or harbour, or release their larvae into new waters. http: //www. epa. qld. gov. au/environmental_manageme nt/water_quality_monitoring/projects/introduced _marine_pests/ • Historically hull fouling was considered a primary vector for transporting species. However, the modern use of metal hulls and anti-fouling paints, decreased port residency times and faster ship speeds, contribute to reduced hull fouling (Marine Invasions Research Lab).
WETLANDS • The invasion of water hyacinths in Zambia is choking lake, river and wetland systems such that local fishing economies are devastated and hydroelectric facilities have been damaged. http: //www. arc. agric. za/institutes/ppri/main/divisions/weedsdiv/hyacinth. htm
TERRESTRIAL ECOSYSTEMS • Most of the previously forested lowland systems on the drier sides of Hawaii are now dominated by the invasive fountain grass (Pennisetum setaceum). This grass has severely altered the ecosystem dynamics of these arid regions by suppressing native vegetation and promoting fires that have proved devastating to the native flora (Cabin et al, 2000).
TERRESTRIAL ECOSYSTEMS cont. • The rapid invasion and spread of alien trees and shrubs of Acacia, Hakea and Pinus species over large areas of fynbos in South Africa, threaten hundreds of native plant species with extinction. They change fire and nutrient-cycling regimes, and greatly reduce streamflow from watersheds (Richardson, 2001).
PARASITES AND PATHOGENS l Pathogens can undermine local food and livestock production, thereby causing hunger and famine. They often damage or kill indigenous species because these species have no defences against them. l Chestnut blight eliminated American chestnuts from approximately 180 million acres in eastern USA. Ten moth species that could survive only on chestnut trees also suffered. Currently another introduced microbe (Phytopthora sp. ) is causing the decline of most of the dominant hardwood forest species along the California coast.
PARASITES AND PATHOGENS cont. l Rinderpest was introduced from Asia to Africa in 1889. The disease travelled 5000 km in 10 years, killing more than 90% of Kenya’s buffalo population, (Daszak et al, 2000). l Some species populations still remain depleted or at risk. l Rinderpest also wiped out most of the cattle in several regions, leading to widespread famine, huge economic losses and social unrest. http: //www. americazoo. com/goto/index/mammals/384. htm
PARASITES AND PATHOGENS cont. l The bubonic plague spread from central Asia through north Africa, Europe and China using a flea vector on an invasive species of rat (Rattus rattus) that originally came from India. l The viruses carrying smallpox and measles spread from Europe into the western hemisphere shortly following European colonisation (Mc. Neely, 1996). l Cholera was introduced into Peru in 1991 from Asia, from ship ballast water. In this case it coincided with an algal bloom, and then a redtide outbreak (dinoflagellates, which are the intermediate hosts of Vibrio cholerae), and sickened more than 300 000 people. http: //azerimammals. aznet. org/azerimammals/Rodets. htm
INVASIONS AT THE GENE LEVEL Genetic bottlenecks l Colonization of introduced species often involves a population bottleneck because the number of initial colonists is often small. However, the loss of genetic variation through genetic drift and the inbreeding effect of small populations are thought to contribute to the increased extinction rate of small populations (Frankham and Ralls, 1998). l So, a newly established population is likely to be much less genetically diverse than the population from which it is derived. The reduced genetic diversity can have two consequences: http: //www. schneiderchildrensh ospital. org/peds_html_fixed/pe ds/infectious/
1. Inbreeding depression may limit population growth and lower the probability that the population will persist 2. Reduced genetic diversity will limit the ability of introduced populations to evolve in their new environments ? ? ? If population bottlenecks are harmful (often leading to extinction), then why are invasive species that have gone through a founding bottleneck so successful? (Allendorf and Lundquist, 2003). ? ? ?
CRYPTIC INVASIONS l l l Many species cannot be assigned to either indigenous or alien status because of their global movements and lack of data to support or dismiss movements of species. These are defined as cryptogenic species (Carlton, 1996). Over the last 150 years, Phragmites australis’ distribution and abundance has increased dramatically in North America. 11 halotypes were native to North America, 2 being widespread, with one of those being the most common (ancestral type). This type replaced native types and expanded into areas where historically P. australis did not grow.
http: //www. huh. harvard. edu/libraries/Robinson_exhibit/plate 49. jpg l Japanese red alga (Polysiphonia harveyi) occurs on North American coasts of the North Atlantic. It is regarded as an alien in the British Isles and Atlantic Europe. Two separate invasive halotypes of P. harveyi were discovered, which originated from two separate introductions.
HYBRIDISATION l Displacement of indigenous by invasive species through hybridisation is called ‘genetic assimilation’ The invasive taxon is integrated into the gene pool of the indigenous species (Petit, 2004). l Should hybrid plants resulting from the cross between an indigenous and alien plant be termed indigenous or alien? According to Petit (2004), hybrids that have at least one alien parent should not be considered as indigenous since they would not be present without human intervention. This is the anthropocentric view. If the biogeographical view were accepted, hybrid taxa would be termed indigenous. (Why? )
HYBRIDISATION cont. l The loss of native fish due to hybridisation between indigenous and alien species has been known for more than 20 years (Miller et al, 1989). l Other hybrids also occur e. g. between different alien species, between their ecotypes, and between previously isolated native species brought together by human activity. l The mallard duck was introduced into SA from Europe, and they are capable of breeding with most species in their genus. They have been known to breed with the yellow-billed duck, which compromises the yellow-bills’ genetic integrity (Dean, 2000). http: //www. petsforum. com/aquageo/Posters/im ages/E 05187. jpg http: //www. kenyabirds. org. uk/y-bill_duck. htm
HYBRIDISATION cont. l In the USA, the most abundant genotype of the alien Tamarix (which has invaded over 600 000 ha of riparian and wetland habitats) is a novel hybrid between two introduced Eurasian species (Gaskin and Schaal, 2002).
HYBRIDISATION cont. http: //www. wcrc. govt. nz/council/pests/spartina. htm l. Spartina http: //www. ew. govt. nz/enviroinfo/pests/plants/spartina. htm anglica represents an example of a fixed hybrid form. Spartina alterniflora from eastern America was introduced in southern England, where hybridisation with the local Spartina maritima resulted in a sterile hybrid. Chromosome doubling in this hybrid gave rise to a new fertile species, Spartina anglica, a vigorous and aggressive perennial plant that has actively been colonising British and western Europe salt marshes since its formation (Petit, 2004).
HYBRIDISATION cont. l. Siemann http: //www. lcsd. gov. hk/LEISURE/LP/gc/plantphoto/image/tree/sase 07 w. jpg and Rogers (2001) found that an invasive tree species, the Chinese tallow tree (Sapium sebiferum), evolved increased competitive ability in their introduced range. Invasive genotypes were larger than native genotypes and produced more seeds, but they had lower quality leaves and invested fewer resources in defending them. Thus, there a number of reasons why introduced genotypes may fare well even though indigenous genotypes may be locally adapted.
Chapter 1 Definitions Chapter 2 History, globalisation and GMOs Chapter 3 The human dimension Chapter 4 Pathways of introduction Chapter 5 Characteristics of invasive alien species Chapter 6 The ecology of biological invasions Next Chapter 7 Impacts of invasive alien species Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 I hope that you found chapter 6 informative and that you will enjoy chapter seven!