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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Invasive species | 4/9 | https://en.wikipedia.org/wiki/Invasive_species | reference | science, encyclopedia | 2026-05-05T07:18:41.562467+00:00 | kb-cron |
Many marine organisms can attach themselves to vessel hulls. Such organisms are easily transported from one body of water to another, and are a significant risk factor for a biological invasion event. Controlling for vessel hull fouling is voluntary and there are no regulations currently in place to manage hull fouling. However, the governments of California and New Zealand have announced more stringent control for vessel hull fouling within their respective jurisdictions. Another vector of non-native aquatic species is ballast water taken up at sea and released in port by transoceanic vessels. Some 10,000 species are transported via ballast water each day. Many of these are harmful. For example, freshwater zebra mussels (Dreissena polymorpha) from Eurasia most likely reached the Great Lakes via ballast water. The mussels outcompete native organisms for oxygen and food, and can be transported in the small puddle left in a supposedly empty ballast tank. Regulations attempt to mitigate such risks, not always successfully. Climate change is causing an increase in ocean temperature. These changes to the environment in turn cause range shifts in organisms, creating new species interactions. For example, organisms in a ballast tank of a ship traveling from the temperate zone through tropical waters may experience temperature fluctuations as much as 20 °C. Heat challenges during transport may enhance the stress tolerance of species in their non-native range, by selecting for genotypes that will survive a second applied heat stress, such as increased ocean temperature in the founder population.
=== Effects of wildfire and firefighting === Invasive species often exploit disturbances to an ecosystem (wildfires, roads, foot trails) to colonize an area. Large wildfires can sterilize soils, while adding nutrients. Invasive plants that can regenerate from their roots then have an advantage over natives that rely on seeds for propagation.
== Adverse effects == Invasive species can affect the invaded habitats, communities, and ecosystems adversely, causing ecological, environmental, and/or economic damage.
=== Ecological === The European Union defines "Invasive Alien Species" as those that are outside their natural distribution area, and that threaten biological diversity. Biotic invasion is one of the five top drivers for global biodiversity loss, and is increasing because of tourism and globalization. This may be particularly true in inadequately regulated fresh water systems, though quarantines and ballast water rules have improved the situation.
Invasive species may drive local native species to extinction via competitive exclusion, niche displacement, or hybridization with related native species. Therefore, besides their economic ramifications, alien invasions may result in extensive changes in the structure, composition and global distribution of the biota at sites of introduction, leading ultimately to the homogenization of the world's fauna and flora and the loss of biodiversity. It is difficult to unequivocally attribute extinctions to a species invasion, though for example there is strong evidence that the extinction of about 90 amphibian species was caused by the chytrid fungus (Batrachochytrium dendrobatidis) spread by international trade. Multiple successive introductions of different non-native species can worsen the total effect, as with the introductions of the amethyst gem clam (Gemma gemma) and the European green crab (Carcinus maenas). The gem clam was introduced into California's Bodega Harbor from the US East Coast a century ago. On its own, it did not displace native clams (Nutricola spp.). However, in the mid-1990s, the introduction of the European green crab resulted in an increase of the amethyst gem at the expense of the native clams. In India, multiple invasive plants have invaded 66% of natural areas, reducing the densities of native forage plants, declining the habitat-use by wild herbivores and threatening the long-term sustenance of dependent carnivores, including tigers. Invasive species can change the functions of ecosystems. For example, invasive plants can alter the fire regime (e.g., cheatgrass, Bromus tectorum), nutrient cycling (e.g., smooth cordgrass, Spartina alterniflora), and hydrology (e.g.,Tamarix) in native ecosystems. Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species. For example, hybridization with introduced cordgrass threatens the existence of California cordgrass (Spartina foliosa) in San Francisco Bay. Invasive species cause competition for native species, and because of this 400 of the 958 endangered species under the Endangered Species Act are at risk.
The unintentional introduction of forest pest species and plant pathogens can change forest ecology and damage the timber industry. Overall, forest ecosystems in the U.S. are widely invaded by exotic pests, plants, and pathogens. The Asian long-horned beetle (Anoplophora glabripennis) was first introduced into the U.S. in 1996, and was expected to infect and damage millions of acres of hardwood trees. As of 2005 thirty million dollars had been spent in attempts to eradicate this pest and protect millions of trees in the affected regions. The woolly adelgid (Adelges tsugae) has inflicted damage on old-growth spruce, fir and hemlock forests and damages the Christmas tree industry. Chestnut blight (Cryphonectria parasitica) and Dutch elm disease (Ascomycota) are plant pathogens with serious impacts. Garlic mustard (Alliaria petiolata) is one of the most problematic invasive plant species in eastern North American forests, where it is highly invasive of the understory, reducing the growth rate of tree seedlings and threatening to modify the forest's tree composition.
Native species can be threatened with extinction through the process of genetic pollution. Genetic pollution is unintentional hybridization and introgression, which leads to homogenization or replacement of local genotypes as a result of either a numerical or fitness advantage of the introduced species. Genetic pollution occurs either through introduction or through habitat modification, where previously isolated species are brought into contact with the new genotypes. Invading species have been shown to adapt to their new environments in a remarkably short amount of time. The population size of invading species may remain small for a number of years and then experience an explosion in population, a phenomenon known as "the lag effect".