By Mohammad Mahassneh
The term invasive alien species (IAS), i.e., a nonnative, nonindigenous, foreign, exotic species, refers to a species, subspecies, or lower taxon that is or has been introduced outside of its natural range (in the past or present) and carries dispersal potential (i.e., might spread outside the range it occupies naturally or could not occupy without the direct or indirect introduction or care by humans). According to the definition issued by the International Union for the Conservation of Nature (IUCN) in 2000, it includes any part, gametes, or propagule of such species that might survive and subsequently reproduce.
The increasing commercialization, globalization, and modernization of travel are causing environmental changes, including climate change, and facilitate the arrival and establishment of IAS. Thus, IAS – including plants, animals, and microorganisms – present a growing environmental and economic threat to biodiversity and affect agricultural crop production, threatening human livelihoods and biodiversity globally. Moreover, IAS are among the most significant drivers of species extinction and ecosystem degradation. These species negatively impact ecosystem services and human well-being and are considered the second-greatest agent of species endangerment and extinction after habitat destruction.
The disturbance of natural habitats promotes the establishment of IAS. On a global scale, the most relevant disturbance factors are the expansion of agriculture, changes in the composition of native communities as a result of climate change (biome shifts), and increasing occurrences of wildfire. Biological invasions are considered a direct driver of biodiversity loss and have a pronounced negative impact on supporting, provisioning, regulating, and cultural services. Both the numbers and distribution of invasive species are increasing in many parts of the world, to the extent that the biogeographic distinctiveness of different regions is becoming blurred.
The global costs of IAS are currently estimated at about US$50 billion per year.
According to IUCN Red Lists, IAS are responsible for more extinctions that have occurred worldwide than any other agent. Globally, almost 20 percent of vertebrates are thought to be in danger of extinction or threatened in some way by invasive species. The impact of IAS extends beyond biodiversity loss to include effects on ecosystem services, agricultural and fisheries production, and water quality and supply – the majority of which are associated with the provisioning of food security (agriculture, fisheries, etc.). The ecological impacts of IAS include habitat alteration, competition and predation, disease transmission, and genetic dilution. While not all alien species have the potential to become invasive or cause problems, there are many that can significantly alter habitats and affect the associated biota or result in a reduction in the quality of economic services.
IUCN assessments find that one-sixth of the global land surface is highly vulnerable to invasion, including substantial areas in developing economies and biodiversity hotspots. The dominant invasion vectors differ between high-income countries (imports, particularly of plants and pets) and low-income countries (air travel). Uniting data on the causes of introduction and establishment can improve early-warning and eradication schemes. Most countries have limited capacity to act against invasions. In particular, a clear need for proactive invasion strategies has been revealed in areas with high poverty levels, high biodiversity, and low historical levels of invasion.
To demonstrate a strong reactive capacity in controlling the spread of already introduced IAS, countries must first recognize that IAS are threatening that country’s environment and economy. They must furthermore have identified the IAS already present and show evidence that an IAS policy can be turned into management actions. To have a strong proactive capacity, countries must attempt to prevent the introduction of IAS that are new to that country and control species that are already established and are beginning to emerge as problematic IAS. Thus, demonstrating proactive capacity requires comprehensive border-control policies and programs for research, monitoring, and public engagement.
The Convention on Biological Diversity (CBD) highlights the adverse effects of IAS. Article 8(h) stipulates: “Each contracting Party shall, as far as possible and as appropriate, prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species.” The Aichi Target 9, made under the CBD, also states that “By 2020, invasive alien species and pathways are identified and prioritized, priority species are controlled or eradicated and measures are in place to manage pathways to prevent their introduction and establishment.”
The typical pattern of establishment for IAS involves an initial lag period after their arrival, followed by the rapid spread. The vectors that facilitate IAS movement also determine their subsequent geographic spread.
To implement this obligation and the related global initiatives (e.g., the Global Invasive Species Database GISD), Palestine, as a contracting party of CBD in 2015, shall set up a national strategy on IAS. It must develop legislation to prevent the introduction of new IAS and the spread of the already present IAS, carry out a risk analysis that uses the available information and communication technology, and provide infrastructure for the control of IAS. The control of IAS is the most cost-effective and frequently feasible only during the lag phase. The future spread of these species threatens the unique assemblage of plants within this world-renowned site, a cost that is difficult to quantify in monetary terms. But its potential constitutes an unquantifiable loss to our biodiversity and natural heritage. Considerable attention should be focused on the various plant and animal species that have been introduced, whether intentionally or accidentally, over the last 100 years or so. Moreover, significant efforts should be directed towards preventing the establishment of cross-border invasive species, which means that we must move towards the development of a national strategy and provide guidance on the control and eradication of the main problematic species.
Furthermore, an overview of the IAS present in Palestine is needed and must include the detailing of the main vectors of spread and the pathways for the various species, also indicating their impact on biodiversity and the associated socioeconomic implications. A proposed strategy for managing IAS at the country level is urgently required. The investigation of IAS in Palestine should follow the hierarchical approach that incorporates three key elements: prevention, early detection and eradication, and control and long-term containment and management.
An ongoing national project on IAS is proceeding with main objectives that include the survey of IAS present in Palestine, the pathways of introduction, the vectors of spread, the techniques to combat and eradicate IAS, and the development of a national strategy to deal with IAS.
There are three main strategies for controlling invasive alien species:
- Their introduction should be prevented in the first place. There should be a ban on intentionally keeping, breeding, cultivating, transporting, placing on the market, and importing invasive alien plants and animals.
- When IAS are introduced unintentionally, the animals must be removed from the environment as quickly as possible. Plants must be destroyed.
- If invasive alien populations are so large that they can no longer be caught or eradicated, measures must be taken to stop them from spreading further.
It is urgent to raise awareness among people working in the fields of animal and public health, making them aware of the need to consider IAS as a health threat. Awareness and action will be influenced by and must consider the wider public perspective, not just researchers and institutions. Initiatives that aim to sensitize citizens about the health threats associated with IAS are needed to promote responsible behavior when crossing borders and to improve the general public attitude toward IAS-control and eradication programs.
IAS may host pathogens that are absent in the area of release and may cause their establishment and subsequent spillover to local species, possibly resulting in an increase of disease risk for humans, domestic animals, and native wildlife. An increase of the local disease risk may also occur if the introduced IAS is susceptible to, and able to transmit, local pathogens. Pathogens acquired by IAS may be amplified and possibly spill back to humans and local species. A first major constraint in addressing the issue of disease emergence connected to IAS is given by the lack of comprehensive data on pathogens that affect IAS. In this sense, we recommend the gathering of an ad hoc database that includes all the available information on IAS pathogens that affect human and animal health, including their geographical distribution and prevalence in IAS populations in both native and introduced ranges. It would also be advisable to improve our understanding of the key epidemiological events and factors that drive the emergence of infectious diseases following IAS establishment. There is an urgent need for research efforts that aim to develop transparent and flexible tools that might be able to prioritize IAS based on the risk of transmitting pathogens with the potential to impact the health of humans, production animals, and native wildlife.
Many of the 100 most dangerous IAS worldwide are established in Palestine, exerting significant threats and adverse impacts on biodiversity, public health, and socioeconomic conditions. Some of these IAS are introduced below.
Acridotheres tristis: The common myna or Indian myna, sometimes spelled mynah, is a member of the family Sturnidae, native to Asia. An omnivorous open woodland bird with a strong territorial instinct, the common myna has adapted extremely well to urban environments.
Ligustrum robustum: Bora-bora, Ceylon privét, Sri Lankan privet, tree privet grows as a shrub or small tree up to 10 meters (30 ft) tall, though old specimens of more than a hundred years have been observed with a height of 15 meters (50 ft). The fruit of the shrub is an ellipsoid berry, bluish-purple when fully ripe, that can reach 7–10 mm × 4–5 mm in size.
Myocastor coypus: The coypu, also known as nutria, Bewerrot, Biberratte, coipù, or coypu, is a large, herbivorous, semiaquatic rodent. Classified for a long time as the only member of the family Myocastoridae, Myocastor is now included within Echimyidae, the family of the spiny rats. The coypu lives in burrows alongside stretches of water and feeds on river plant stems. Originally native to subtropical and temperate South America, it has since been introduced to North America, Europe, Asia, and Africa, primarily by fur farmers. Although it is still hunted and trapped for its fur in some regions, its destructive burrowing and feeding habits often bring it into conflict with humans, and it is considered an invasive species.
Rattus rattus: The black rat, also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus Rattus, in the subfamily Murinae. It likely originated in the Indian subcontinent but is now found worldwide as an invasive species.
Ailanthus altissima: Known as Chinese sumac, tree of heaven, or stinking, this is a very aggressive plant and a prolific seed producer (up to 350,000 seeds in a year) that grows rapidly and can overrun native vegetation. It also produces toxins that prevent the establishment of other plant species. The root system is aggressive enough to cause damage to sewers and foundations.
Prosopis juliflora var. juliflora (Sw.) DC. Known as Prosopis, Mathenge (Kenya), mesquite, algarroba, ironwood eterai (Turkana), this species belongs to the family Fabaceae (Leguminosae) and the subfamily Mimosoideae. Prosopis juliflora is invasive in parts of Palestine, mainly the Jordan Valley. Prosopis juliflora thrives in most soils, including sandy, rocky, poor, and saline soils within an altitude range of 300–1,900 meters above sea level. Its deep taproots help it access subsurface waters.
Ambrosia artemisiifolia, also known by the common names common ragweed, annual ragweed, and low ragweed, is a species of the genus Ambrosia, native to regions of the Americas. Ambrosia artemisiifolia is a widespread invasive species and can become a noxious weed. Its windblown pollen is highly allergenic.