Many scientists have been asked this question and have sought 
response among invasive species in different areas. However, the information shows that there is no single explanation, but it depends on both the ecosystem and the species involved. Still have also detected some general patterns that seem to recur in different parts of the world. Among the reasons behind the success of the invaders, we differentiate between those that are related to the characteristics of the receiving ecosystem and those that are typical of invasive species.
features of ecosystems that house a higher proportion of invasive species. Although no ecosystem on Earth that does not have invasive species from their biological bitter, it is also true that there are areas with higher proportion of exotic species than others. For example, island ecosystems are considered "fragile" where the introduction of exotic often has more drastic consequences on the continents. Also disturbed environments are more likely to hold alien species than those stable and well maintained. Two hypotheses help to explain this pattern:
The empty niche hypothesis posits that some ecosystem functions may not be performed for any species because phylogenetic and biogeographic constraints. For example, treeless ecosystems such as temperate grasslands of South America. But this does not mean that no tree can live there but trees neighboring regions have not been able to colonize the territory. However, recently introduced several species of exotic pines (Pinus halepensis as and P. radiata), which not only fully support the environmental conditions, but spread rapidly due to the absence of other trees with to compete.
The hypothesis of the absence of enemies postulated that the success of some invasive because they invade the ecosystem there are no predators, parasites or diseases, able to halt its spread. The poverty of the island's characteristic species or caused by disturbance reduce the likelihood that an invasive species found resistance from competitors, predators or diseases in these environments.
intrinsic characteristics of invasive species.
1. High rates of growth and reproduction. Both characters lead to an effective monopolization of resources and displacement of native species by competitive exclusion. For example, some invasive trees and ditch banks, such as ailanthus (Ailanthus altissima ), the black locust (Robinia pseudoacacia ) or maple box elder (Acer negundo ), grow rapidly, produce abundant crops of seeds every year and / or generate abundant vegetative regrowth. In animals, example, the ability of parthenogenesis is a great advantage (a female can have children without being fertilized by a male), eg in the case of small aquatic snail Potamopyrgus antipodarum from New Zealand, which has spread great success in Australia, Europe and America, the arrival of a single female into a river or lake can result in a large population, because their reproductive rate is very high.
2. Flexibility and phenotypic plasticity. Several authors have suggested that invasive species are able to acclimate more and better than native species to new or changing environmental conditions. This capacity for acclimatization may be due to a high phenotypic plasticity, where a particular genotype gives rise to very different phenotypes in response to the environment, or a functional flexibility, ie, the phenotype may vary over time in response to environmental fluctuations. Moreover, phenotypic plasticity can vary not only between invasive and noninvasive, but between populations within a species that show different invasiveness. Such is the case of the indigenous relict of hornbeam (Rhododendron ponticum ) in southern Spain, showing a low phenotypic plasticity compared with invasive populations of this species in central European cities, whose plasticity is very high .
3. Facility for hybridization. Some species have very easy to hybridize with each other, allowing them to increase their genetic variability. This ability may confer a potential invader, as it encourages the establishment of stable populations in new areas from a few individuals introduced. As an example, include the case of the Ruddy Duck (Oxyura jamaicensis ), a species introduced in England in the forties, which has been hybridized with our native species, the White-headed Duck (Oxyura leucocephala ). The hybrids are fertile and can cross each other and with parents, contributing to expansion of the ruddy duck at the expense of a loss of the original characters of the indigenous species.
response among invasive species in different areas. However, the information shows that there is no single explanation, but it depends on both the ecosystem and the species involved. Still have also detected some general patterns that seem to recur in different parts of the world. Among the reasons behind the success of the invaders, we differentiate between those that are related to the characteristics of the receiving ecosystem and those that are typical of invasive species. features of ecosystems that house a higher proportion of invasive species. Although no ecosystem on Earth that does not have invasive species from their biological bitter, it is also true that there are areas with higher proportion of exotic species than others. For example, island ecosystems are considered "fragile" where the introduction of exotic often has more drastic consequences on the continents. Also disturbed environments are more likely to hold alien species than those stable and well maintained. Two hypotheses help to explain this pattern:
The empty niche hypothesis posits that some ecosystem functions may not be performed for any species because phylogenetic and biogeographic constraints. For example, treeless ecosystems such as temperate grasslands of South America. But this does not mean that no tree can live there but trees neighboring regions have not been able to colonize the territory. However, recently introduced several species of exotic pines (Pinus halepensis as and P. radiata), which not only fully support the environmental conditions, but spread rapidly due to the absence of other trees with to compete.
The hypothesis of the absence of enemies postulated that the success of some invasive because they invade the ecosystem there are no predators, parasites or diseases, able to halt its spread. The poverty of the island's characteristic species or caused by disturbance reduce the likelihood that an invasive species found resistance from competitors, predators or diseases in these environments.
intrinsic characteristics of invasive species.
1. High rates of growth and reproduction. Both characters lead to an effective monopolization of resources and displacement of native species by competitive exclusion. For example, some invasive trees and ditch banks, such as ailanthus (Ailanthus altissima ), the black locust (Robinia pseudoacacia ) or maple box elder (Acer negundo ), grow rapidly, produce abundant crops of seeds every year and / or generate abundant vegetative regrowth. In animals, example, the ability of parthenogenesis is a great advantage (a female can have children without being fertilized by a male), eg in the case of small aquatic snail Potamopyrgus antipodarum from New Zealand, which has spread great success in Australia, Europe and America, the arrival of a single female into a river or lake can result in a large population, because their reproductive rate is very high.
2. Flexibility and phenotypic plasticity. Several authors have suggested that invasive species are able to acclimate more and better than native species to new or changing environmental conditions. This capacity for acclimatization may be due to a high phenotypic plasticity, where a particular genotype gives rise to very different phenotypes in response to the environment, or a functional flexibility, ie, the phenotype may vary over time in response to environmental fluctuations. Moreover, phenotypic plasticity can vary not only between invasive and noninvasive, but between populations within a species that show different invasiveness. Such is the case of the indigenous relict of hornbeam (Rhododendron ponticum ) in southern Spain, showing a low phenotypic plasticity compared with invasive populations of this species in central European cities, whose plasticity is very high .
3. Facility for hybridization. Some species have very easy to hybridize with each other, allowing them to increase their genetic variability. This ability may confer a potential invader, as it encourages the establishment of stable populations in new areas from a few individuals introduced. As an example, include the case of the Ruddy Duck (Oxyura jamaicensis ), a species introduced in England in the forties, which has been hybridized with our native species, the White-headed Duck (Oxyura leucocephala ). The hybrids are fertile and can cross each other and with parents, contributing to expansion of the ruddy duck at the expense of a loss of the original characters of the indigenous species.
