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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Invasive species | 2/9 | https://en.wikipedia.org/wiki/Invasive_species | reference | science, encyclopedia | 2026-05-05T07:18:41.562467+00:00 | kb-cron |
Island ecosystems may be more prone to invasion because their species face few strong competitors and predators, and because their distance from colonizing species populations makes them more likely to have "open" niches. For example, native bird populations on Guam have been decimated by the invasive brown tree snake (Boiga irregularis). However, the geographical distance and open water characteristic of island ecosystems can also delay colonisation by invasive species. For example, island nations such as Australia and the Galapagos have a high proportion of their island ecology consisting of endemic species due to immigration of other species being limited by oceans and their geographical isolation. In New Zealand the first invasive species were the dogs and rats brought by Polynesian settlers around 1300. These and other introductions devastated endemic New Zealand species. The colonization of Madagascar brought similar harm to its ecosystems. Logging has caused harm directly by destroying habitat, and has allowed non-native species such as prickly pear (Opuntia) and silver wattle (Acacia dealbata) to invade. The water hyacinth (Pontederia crassipes) forms dense mats on water surfaces, limiting light penetration and hence harming aquatic organisms, and creating substantial management costs. The shrub lantana (Lantana camara) is now considered invasive in over 60 countries, and has invaded large geographies in several countries prompting aggressive federal efforts to control it. Along with island ecosystems, intensively managed fenced areas are more prone to invasion. One reason is that species can enter through ways that fences cannot block. In the case of many plant species, dispersal can occur through wind, water, and birds carrying seeds either internally or externally. Small animals or insects are sometimes also able to make it through fenced areas. Another reason is that intensive management methods create opportunities for these invasive species to thrive. When fenced areas are established, they are intensively managed through clearing vegetation, mowing, and disturbing the soil. This reduces competition from the native plant species in the area and exposes the soil so that invasive species can easily populate the area. The purpose of these fenced areas is often to keep unwanted herbivores out of the areas. Because there are no threats to the invasive plants that can take over intensively managed fenced areas, they can flourish without predatory threats. Finally, in general, invasive species have traits that favor their survival. Most invasive species are extremely resilient and have traits that favor their establishment in areas where they are not native. These traits, along with the intensive management of the fenced areas, create an ideal environment in which these invasive species can thrive. Primary geomorphological effects of invasive plants are bioconstruction and bioprotection. For example, kudzu (Pueraria montana), a vine native to Asia, was widely introduced in the southeastern United States in the early 20th century to control soil erosion. The primary geomorphological effects of invasive animals are bioturbation, bioerosion, and bioconstruction. For example, invasions of the Chinese mitten crab (Eriocheir sinensis) have resulted in higher bioturbation and bioerosion rates. A native species can also become harmful and effectively invasive to its native environment after human alterations to its food web. This has been the case with the purple sea urchin (Strongylocentrotus purpuratus), which has decimated kelp forests along the northern California coast due to overharvesting of its natural predator, the California sea otter (Enhydra lutris).
=== Species-based mechanisms ===
Invasive species appear to have specific traits or specific combinations of traits that allow them to outcompete native species. In some cases, these characteristics include rates of growth and reproduction. In other cases, invasive species interact with native species other more directly. One study found that 86% of invasive species could be identified from such traits alone. Another study found that invasive species often had only a few of the traits, and that noninvasive species had these also. Common invasive species traits include fast growth and rapid reproduction, such as vegetative reproduction in plants; association with humans; and prior successful invasions. Domestic cats (Felis catus) are effective predators of wildlife. They have become feral and invasive in places such as the Florida Keys. An introduced species might become invasive if it can outcompete native species for resources. If these species evolved under great competition or predation, then the new environment may host fewer able competitors, allowing the invader to proliferate. Ecosystems used to their fullest capacity by native species can be modeled as zero-sum systems, in which any gain for the invader is a loss for the native. However, such unilateral competitive superiority (and extinction of native species with increased populations of the invader) is not the rule.