Invasibility

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Invasive plants at Cranny, Omagh Alien plants at Cranny, Omagh - geograph.org.uk - 415678.jpg
Invasive plants at Cranny, Omagh

Alien species, or species that are not native, invade habitats and alter ecosystems around the world. Invasive species are only considered invasive if they are able to survive and sustain themselves in their new environment. [1] A habitat and the environment around it has natural flaws that make them vulnerable to invasive species. [1] The level of vulnerability of a habitat to invasions from outside species is defined as its invasibility. One must be careful not to get this confused with invasiveness, which relates to the species itself and its ability to invade an ecosystem. [2]

Contents

There are many factors, abiotic and biotic, that can raise or lower a habitat's invasibility, such as stress, disturbance, nutrient levels, climate, and pre-existing native species. Typically invasive species favor areas that are nutrient-rich, have few environmental stresses, and high levels of disturbances. This explains why areas in the United States such as Hawaii, Florida, and California are infested with invasive species. [3] These invasions are one of the biggest and most consistent threats to biodiversity across the globe. Antarctica is the only natural reserve on Earth that is without invasive species, due to its environmental factors. [2]

Ecological factors

Abiotic factors

Abiotic factors serve as the first filter of invasive species within a respective habitat. [4] Invasive species are typically limited to habitats that are ecologically similar to their native habitats. [5] The relative efficiency of invasibility is dependent on the abiotic niche being conserved over time or if the invader is able to adapt rapidly to their newly invaded abiotic niche. [6] For example, the Asian shore crab (Hemigrapsus sanguineus) has almost identical abiotic niches in its native and invaded habitat [7] but the European Green Crab (Carcinus maenas) has the ability to adapt its abiotic niche as it can survive in a wide range of water temperatures and salinities. [4] Some invasions are only dependent on abiotic factors and not biotic factors. For example, the invasion of cordgrass (Spartina anglica) in salt marshes was highly dependent on salinity and sediment type and no biotic factors. [4]

Propagule pressure is a composite measure of the number of individuals of a species released into a region to which they are not native. It has been found that species with weak dispersal agents create increased invasibility, especially near stream sides.[ citation needed ] The absence of habitat fragmentation allows for greater dispersal and high invasibility at edges of habitat boundaries.[ citation needed ] Propagule pressure is the main reason why the density of some invasive species is higher near the site of introduction.[ citation needed ]

Disturbance is another abiotic factor that can affect invasibility. Disturbance is defined as a punctuated event that kills organisms or removes part of their biomass. [8] Both increasing and suppressing disturbances can increase invisibility. For example, in the North America n grasslands fire was found to decrease invasion but increased grazing increased invasion. [8] Fires increase the invasibility of some species of pine trees but decreases the invasibility of other pine species. [8] It has been proposed that disturbances increase invasibility to the degree that they cause the natural habitat to deviate from its original state. [8]

Stresses such as nutrient availability, water availability, light availability and extreme conditions affect invasibility. Low stress environments increase invasibility because the invaders are more likely to be able to take advantage of the increased resources. [4] Addition of nutrients has been found to enhance the invasibility of an area. [4] For example, when nutrients were added to an aquatic plankton environment it resulted in increased bacteria growth which facilitated the invasion of ciliates since the competition for resources was decreased. [9] Also, nutrient addition to grasslands can have a variety of effects as it can shift species composition towards or away from a smaller number of relatively fast growing species, woody species such as annual herbs, perennial herbs, grasses or shrubs. [8] Nutrient addition to a nutrient poor environment can not only promote invasions but can prompt the eventual dominance of non-native species within the habitat. [10] Large scale nutrient addition can have a significant positive impact on invasibility. For example, large scale nutrient run-off in the New England area has caused the invasion of Phragmites australis an exotic vascular plant. [4] Limiting nutrient resources has a negative impact on invasibility as resources will be limited increasing the competition between invasive and native species. For example, there is decreased water flow inside eelgrass habitats thus eelgrass limits the growth and survival of the invasive mussel ( Musculista senhousia ) This reduces the extent of its invasion compared to areas where eelgrass meadows are fragmented or absent. [11] Stresses that limit metabolism or resource acquisition - such as extreme temperature and toxins - has the ability to both increase or decrease invasibility; this is dependent on the invader's characteristics. [4] If the invader can live in a wider temperature range than the native species it will have a greater success rate. For example, an invasive C4 plant would have a better chance of surviving than a native C3 plant during a drought. [4]

Biotic factors

The Asian shore crab (Hemigrapsus sanguineus) invades shorelines around the world, especially in the New England area. Hemigrapsus sanguineus.jpg
The Asian shore crab (Hemigrapsus sanguineus) invades shorelines around the world, especially in the New England area.

There are variety of biotic factors that influence invasibility such as competition, diversity, predation and disease. One of the main biotic factors that impact invasibility is interspecific competition. Since an invader will require certain limiting resources it will be more likely to be successful in habitat where competition for these resources is low. [8] If the invader has optimum performance at a resource level that only slightly overlaps with a native species than it will have a greater chance invasion. [4] For example, another reason the Asian shore crab (Hemigrapsus sanguineus) is such a successful invader in the New England area is because there are few ecological equivalents - that is to say, other grapsid crabs in the area. [7] However, determining the success of a non-native species in its invaded habitat is not always easy because their resource requirements may differ from their native habitat. [8] When the characteristics of a non-native species and native species are significantly similar a single native species can go a long way to prevent the invasion of a non-native species. [8]

A habitat with high species diversity results in lower total resource availability thus decreasing the success of an invader. [8] Diverse habitats also maintain stronger indirect interactions between species thus causing exclusion of non-native species that could out-compete a native species on a one-to-one level. [8] A notable exception is diverse habitats with many pollinators. Pollinators significantly increase the invasion success of invasive plants thus habitats with a diverse set of pollinators have a greater chance of being invaded. [8]

Habitats with high invasibility

Certain habitats are naturally more susceptible to alien plant invasions. Invasive plants tend to thrive in nutrient-rich and man-made habitats. [1] The most commonly invaded types of habitats include those that are man made, such as gardens, farmlands, urban landscapes, ecosystems with nutrient rich fertile soil, such as forestry plantations and forest clearings, or areas of high levels of disturbance, such as coastal and riparian habitats. [1] [12] Habitats with high levels of disturbance are much more likely to be invaded by a non-native species. In order for successful invasion of a natural community to occur, it requires dispersal, establishment, and survival. [13]

Central Californian Coastline, Big Sur, May 2013 Central Californian Coastline, Big Sur - May 2013.jpg
Central Californian Coastline, Big Sur, May 2013

The specific ecosystems in the United States that are among the most heavily invaded are located in Hawaii, Florida, and California. Specifically, the grasslands and valleys of California have been so heavily invaded by non-native species, that this habitat has been completely altered, and the original habitat composition and structure are not known because of how different it is now. [3] In this same region, the southwest piñon-juniper woodlands have only experienced light habitat invasion from non-natives. It was also found that large oceanic bays such as the Chesapeake Bay in Virginia and Maryland and the San Francisco bay [ specify ] in California now contain more non-native species than native species that the habitat originated with.[ citation needed ] However, the worst of all in the United States is Hawaii. The island state is the most heavily invaded region in the country. Over the years, over 38 land birds, 18 exotic mammals, 17 exotic reptiles, 38 exotic land mollusks, and 19 exotic freshwater fish have all been successfully introduced to Hawaii, increasing the number; 4,598 exotic species established in the wild. [14] For a small area of a few islands, these are huge numbers, which have very significantly affected the overall ecosystem on the island.

Habitats with low invasibility

Levels of species invasion are low in harsh climates and habitats with poor nutrients. [1] These habitats include mountains, cliffs, bogs, dry grasslands and coniferous woodlands, deserts, and savannas. [1] Non-native plants and animals do not tend to thrive in these types of habitats due to the lack of nutrient availability, harsh climatic conditions, or other unfavorable conditions that diminish the quality of life of a foreign species. [12]

A good example of an area that expresses low invasibility would be the Mojave Desert located in Southern California. The climate here is classified as an arid desert with low soil nutrients and low diversity of species, because the typical resources that common species need in order to stay alive are not readily available in desert habitat conditions. It is extremely hard for any new non-native species to invade this area and live to reproduce. (However, on the other hand "Because overall levels of soil nutrients in the Mojave Desert are low relative to other ecosystems, the high nutrient concentrations that produce high cover of competitive natives that hinders the establishment and growth of aliens may never be found in this region." [15] ) New species are less likely to be able to establish themselves in harsh climate areas, or communities that are abiotically stressful.

Related Research Articles

Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way.

<span class="mw-page-title-main">Ecosystem</span> Community of living organisms together with the nonliving components of their environment

An ecosystem is a system that environments and their organisms form through their interaction. The biotic and abiotic components are linked together through nutrient cycles and energy flows.

<span class="mw-page-title-main">Ecological niche</span> Fit of a species living under specific environmental conditions

In ecology, a niche is the match of a species to a specific environmental condition. It describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [and] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".

<span class="mw-page-title-main">Invasive species</span> Non-native organism causing damage to an established environment

An invasive or alien species is an introduced species to an environment that becomes overpopulated and harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native species that become harmful to their native environment after human alterations to its food web – for example, the purple sea urchin which has decimated kelp forests along the northern California coast due to overharvesting of its natural predator, the California sea otter. Since the 20th century, invasive species have become a serious economic, social, and environmental threat worldwide.

<span class="mw-page-title-main">Edge effects</span> Ecological concept

In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range. As the edge effects increase, the boundary habitat allows for greater biodiversity.

This glossary of ecology is a list of definitions of terms and concepts in ecology and related fields. For more specific definitions from other glossaries related to ecology, see Glossary of biology, Glossary of evolutionary biology, and Glossary of environmental science.

Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation. There are three basic types of freshwater ecosystems: Lentic, lotic and wetlands. Freshwater ecosystems contain 41% of the world's known fish species.

Realized niche width is a phrase relating to ecology, is defined by the actual space that an organism inhabits and the resources it can access as a result of limiting pressures from other species. An organism's ecological niche is determined by the biotic and abiotic factors that make up that specific ecosystem that allow that specific organism to survive there. The width of an organism's niche is set by the range of conditions a species is able to survive in that specific environment.

In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them underpin biology as a whole. They affect a plethora of species, in all forms of environmental conditions, such as marine or land animals. Humans can make or change abiotic factors in a species' environment. For instance, fertilizers can affect a snail's habitat, or the greenhouse gases which humans utilize can change marine pH levels.

<span class="mw-page-title-main">Aquatic ecosystem</span> Ecosystem in a body of water

An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.

Ecologically, invader potential is the qualitative and quantitative measures of a given invasive species probability to invade a given ecosystem. This is often seen through climate matching. There are many reasons why a species may invade a new area. The term invader potential may also be interchangeable with invasiveness. Invader potential is a large threat to global biodiversity. It has been shown that there is an ecosystem function loss due to the introduction of species in areas they are not native to.

<span class="mw-page-title-main">Disturbance (ecology)</span> Temporary change in environmental conditions that causes a pronounced change in an ecosystem

In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements. A disturbance can also occur over a long period of time and can impact the biodiversity within an ecosystem.

Ecological facilitation or probiosis describes species interactions that benefit at least one of the participants and cause harm to neither. Facilitations can be categorized as mutualisms, in which both species benefit, or commensalisms, in which one species benefits and the other is unaffected. This article addresses both the mechanisms of facilitation and the increasing information available concerning the impacts of facilitation on community ecology.

Biotic stress is stress that occurs as a result of damage done to an organism by other living organisms, such as bacteria, viruses, fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants. It is different from abiotic stress, which is the negative impact of non-living factors on the organisms such as temperature, sunlight, wind, salinity, flooding and drought. The types of biotic stresses imposed on an organism depend the climate where it lives as well as the species' ability to resist particular stresses. Biotic stress remains a broadly defined term and those who study it face many challenges, such as the greater difficulty in controlling biotic stresses in an experimental context compared to abiotic stress.

Island ecology is the study of island organisms and their interactions with each other and the environment. Islands account for nearly 1/6 of earth’s total land area, yet the ecology of island ecosystems is vastly different from that of mainland communities. Their isolation and high availability of empty niches lead to increased speciation. As a result, island ecosystems comprise 30% of the world’s biodiversity hotspots, 50% of marine tropical diversity, and some of the most unusual and rare species. Many species still remain unknown.

<span class="mw-page-title-main">Invasive earthworms of North America</span>

Invasive species of earthworms from the suborder Lumbricina have been expanding their range in North America. Earthworms are considered one of the most abundant macroinvertebrates in the soil of ecosystems in temperate and tropical climates. There are around 3,000 species known worldwide. They are considered keystone species in their native habitats of Asia and Europe because, as detritivores, they alter many different variables of their ecosystem. Their introduction to North America has had marked effects on the nutrient cycles and soil profiles in temperate forests. These earthworms increase the cycling and leaching of nutrients by breaking up decaying organic matter and spreading it into the soil. This thins out the soil rapidly because earthworms do not require a mate to reproduce, allowing them to spread fast. Since plants native to these northern forests are evolutionarily adapted to the presence of thick layers of decaying organic matter, the introduction of worms can lead to a loss of biodiversity as young plants face less nutrient-rich conditions. Some species of trees and other plants may be incapable of surviving such changes in available nutrients. This change in the plant diversity in turn affects other organisms and often leads to increased invasions of other exotic species as well as overall forest decline. They are considered one of the most invasive animals in the Midwestern United States along with feral swine.

<span class="mw-page-title-main">Riparian-zone restoration</span> Ecological restoration of river banks and floodplains

Riparian-zone restoration is the ecological restoration of riparian-zonehabitats of streams, rivers, springs, lakes, floodplains, and other hydrologic ecologies. A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth; the habitats of plant and animal communities along the margins and river banks are called riparian vegetation, characterized by aquatic plants and animals that favor them. Riparian zones are significant in ecology, environmental management, and civil engineering because of their role in soil conservation, their habitat biodiversity, and the influence they have on fauna and aquatic ecosystems, including grassland, woodland, wetland or sub-surface features such as water tables. In some regions the terms riparian woodland, riparian forest, riparian buffer zone, or riparian strip are used to characterize a riparian zone.

Privets are any of a number of shrubs or trees in the genus Ligustrum, many of which are invasive. The genus contains about 50 species native to the Old World and Australasia. Many members of the genus are grown as ornamental plants in parts of the world.

Garden waste, or green waste dumping is the act of discarding or depositing garden waste somewhere it does not belong.

<span class="mw-page-title-main">Climate change and invasive species</span> Increase of invasive organisms caused by climate change

Climate change and invasive species refers to the process of the environmental destabilization caused by climate change. This environmental change facilitates the spread of invasive species — species that are not historically found in a certain region, and often bring about a negative impact to that region's native species. This complex relationship is notable because climate change and invasive species are also considered by the USDA to be two of the top four causes of global biodiversity loss.

References

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