Invaders and integrators.
In very simple terms an invasive species is a non-native organism (plant, animal, fungus, or microbe) that is introduced to a new environment.
When this happens the results tend to be negative and are more often than not caused by human activities and this is often what we refer to when talking about invasive species.
The harm caused by invasive species can be roughly categorised as being ecological, economic and human centric such as disease, recreation and aesthetics.
Invasive species can have profound ecological impacts, as seen through various case studies from the UK. One notable example is the grey squirrel (Sciurus carolinensis), which was introduced from North America in the 19th century. The grey squirrel has outcompeted the native red squirrel (Sciurus vulgaris) for resources such as food and habitat. Grey squirrels are more adaptable and have a higher reproductive rate, leading to a significant decline in red squirrel populations. Additionally, grey squirrels carry the squirrel pox virus, which is lethal to red squirrels but does not affect them, further exacerbating the problem.
Lets look at 5 problematic invasive species affecting the UK in a little detail.
American Signal Crayfish
The American signal crayfish (Pacifastacus leniusculus) is an invasive species in the UK, causing significant ecological and economic problems. They outcompete native crayfish, particularly the white-clawed crayfish (Austropotamobius pallipes), for resources, leading to biodiversity loss. Their predation on invertebrates, fish eggs, and juveniles disrupts local food webs and reduces native species. Additionally, signal crayfish carry crayfish plague (Aphanomyces astaci), which is lethal to native crayfish and has caused population declines.
Signal crayfish also destabilize riverbanks and increase sedimentation through burrowing, affecting water quality and aquatic habitats. Their feeding on aquatic vegetation reduces plant biomass and diversity, impacting species that rely on these plants.
Economically, their burrowing damages riverbanks, dams, and irrigation systems, leading to higher maintenance costs and potential structural failures. The decline in native fish populations due to signal crayfish affects commercial fisheries and aquaculture operations. Efforts to control signal crayfish populations are costly and involve trapping, biocides, habitat modification, and public education.
The introduction of signal crayfish to the UK began in the 1970s for aquaculture purposes and as a potential food source. However, they escaped from these environments into the wild and rapidly spread through rivers and water systems. Their ability to thrive in various conditions and their high reproductive rate facilitated their widespread establishment.
Signal crayfish alter aquatic food webs by preying on invertebrates and fish larvae, causing a cascading effect on other species. They impact ecosystem services such as water purification and nutrient cycling by increasing sediment suspension, reducing water clarity, and affecting plant photosynthesis.
Their invasiveness is due to high reproductive capacity, with females producing hundreds of eggs per season, and their broad tolerance to varying environmental conditions.
Management strategies include preventive measures like strict regulations on crayfish transport and public education on their impact. Control techniques involve trapping, researching biological control methods, and using biocides, though these have risks. Restoration efforts aim to rebuild native crayfish populations and habitats.
Himalayan balsam (Impatiens glandulifera) is an invasive plant species in the UK, causing significant ecological and economic problems. It outcompetes native plants for light, space, and nutrients, leading to biodiversity loss. Its dense growth suppresses other vegetation, reducing habitat quality for wildlife. The plant's prolific seed production and explosive seed dispersal enable rapid spread along waterways and disturbed areas.
Himalayan Balsam
Himalayan balsam also impacts riverbanks by destabilising soil through shallow root systems, increasing erosion and sedimentation in water bodies. This affects water quality and aquatic habitats. Its dieback in winter leaves banks bare and more susceptible to erosion, further impacting plant and animal communities.
Economically, managing Himalayan balsam infestations is costly. Efforts include mechanical removal, chemical treatments, and public awareness campaigns. The plant's impact on riverbanks can lead to increased flood risk and higher costs for flood management and infrastructure repair.
Himalayan balsam was introduced to the UK in the early 19th century as an ornamental plant. Its attractive flowers and rapid growth made it popular in gardens, but it quickly escaped cultivation. It spread extensively along rivers, streams, and wetland areas, aided by its ability to thrive in various conditions and its high reproductive rate.
The plant alters ecosystems by forming dense stands that outcompete native vegetation, reducing species diversity. Its flowers attract pollinators, potentially diverting them from native plants and disrupting local pollination networks. The dieback of Himalayan balsam in winter leaves gaps in vegetation cover, which can lead to increased erosion and nutrient loss.
Control strategies for Himalayan balsam include mechanical removal, where plants are pulled or cut before seeding, and chemical treatments with herbicides. Biological control methods, such as introducing natural enemies like rust fungus, are being researched. Public awareness campaigns aim to educate people about the plant's impact and encourage community involvement in removal efforts.
Preventive measures include regulating the sale and planting of Himalayan balsam and promoting native plant species in gardens and landscaping. Restoration efforts focus on re-establishing native vegetation and stabilizing riverbanks to reduce erosion and improve habitat quality.
Rhododendron ponticum is an invasive plant species in the UK, causing significant ecological and economic problems. It outcompetes native plants for light, space, and nutrients, leading to biodiversity loss. Its dense growth forms thickets that suppress other vegetation, reducing habitat quality for wildlife. The plant's vigorous growth and ability to regenerate from cut stumps enable rapid spread in woodlands and heathlands.
Rhododendron ponticum
Rhododendron ponticum also impacts forest ecosystems by creating a dense canopy that blocks light, inhibiting the growth of understory plants. This leads to a decline in native flora and alters habitats for animals. Its leaf litter and dead wood increase soil acidity and alter nutrient cycling, further affecting native plant communities.
Economically, managing Rhododendron ponticum infestations is costly. Efforts include mechanical removal, chemical treatments, and long-term monitoring. The plant's impact on forestry and conservation areas can lead to increased management costs and reduced biodiversity, affecting ecosystem services and tourism.
Rhododendron ponticum was introduced to the UK in the late 18th century as an ornamental plant and for game cover in estates. Its attractive flowers and evergreen foliage made it popular in gardens, but it quickly escaped cultivation. It spread extensively in suitable habitats, aided by its tolerance to a range of conditions and its high reproductive rate.
The plant alters ecosystems by forming dense stands that outcompete native vegetation, reducing species diversity. Its flowers attract pollinators, potentially diverting them from native plants and disrupting local pollination networks. The dense thickets of Rhododendron ponticum can also harbor pests and diseases that threaten native plants.
Control strategies for Rhododendron ponticum include mechanical removal, where plants are cut or uprooted, and chemical treatments with herbicides. Ongoing monitoring and follow-up treatments are essential to prevent regrowth. Biological control methods, such as introducing natural enemies, are being researched. Public awareness campaigns aim to educate people about the plant's impact and encourage community involvement in removal efforts.
Preventive measures include regulating the sale and planting of Rhododendron ponticum and promoting native plant species in gardens and landscaping. Restoration efforts focus on re-establishing native vegetation and improving habitat quality in affected areas.
Japanese knotweed (Fallopia japonica) is an invasive plant species in the UK, causing significant ecological and economic problems. It outcompetes native plants for light, space, and nutrients, leading to biodiversity loss. Its dense growth suppresses other vegetation, reducing habitat quality for wildlife. The plant's aggressive spread via extensive rhizome networks makes it difficult to control and eradicate.
Japanese knotweed
Japanese knotweed also impacts riverbanks and urban areas by destabilising soil through its robust root systems, increasing erosion and sedimentation in water bodies. This affects water quality and aquatic habitats. In urban areas, its roots can damage buildings, roads, and other infrastructure, leading to costly repairs.
Economically, managing Japanese knotweed infestations is expensive. Efforts include mechanical removal, chemical treatments, and long-term monitoring. Its impact on property values and development projects can lead to financial losses and legal disputes. The plant's presence can delay construction projects and increase costs for site clearance and remediation.
Japanese knotweed was introduced to the UK in the mid-19th century as an ornamental plant and for erosion control. Its attractive foliage and rapid growth made it popular in gardens, but it quickly escaped cultivation. It spread extensively along waterways, railways, and disturbed areas, aided by its ability to thrive in various conditions and its vigorous growth.
The plant alters ecosystems by forming dense stands that outcompete native vegetation, reducing species diversity. Its extensive root system can penetrate and damage infrastructure, leading to increased maintenance costs. The dense growth of Japanese knotweed can also hinder access to recreational areas and natural habitats, impacting tourism and conservation efforts.
Control strategies for Japanese knotweed include mechanical removal, where plants are cut or excavated, and chemical treatments with herbicides. Ongoing monitoring and follow-up treatments are essential to prevent regrowth. Biological control methods, such as introducing natural enemies like the psyllid insect (Aphalara itadori), are being researched. Public awareness campaigns aim to educate people about the plant's impact and encourage community involvement in removal efforts.
Preventive measures include regulating the sale and planting of Japanese knotweed and promoting native plant species in gardens and landscaping. Restoration efforts focus on re-establishing native vegetation and improving habitat quality in affected areas.
The Asian hornet (Vespa velutina) is an invasive species in the UK, causing significant ecological and economic problems. It preys on native pollinators, particularly honeybees, leading to biodiversity loss and negatively impacting pollination services essential for ecosystems and agriculture. The aggressive predation on honeybee colonies can result in their decline, which affects crop production and native plant reproduction.
The Asian Hornet
Asian hornets also pose a direct threat to humans, as their stings can be more painful and dangerous than those of native wasps and bees. Multiple stings can cause severe allergic reactions and, in rare cases, fatalities. Their presence increases the risk of stings, particularly for individuals working or engaging in outdoor activities.
Economically, managing Asian hornet infestations is costly. Efforts include monitoring, nest destruction, and public awareness campaigns. The decline in honeybee populations due to hornet predation affects honey production and the agricultural sector, leading to financial losses. The increased costs of pest control and healthcare due to stings also impact the economy.
The introduction of Asian hornets to the UK likely occurred through the accidental transport of goods from Asia. First detected in France in 2004, they have rapidly spread across Europe, reaching the UK by 2016. Their adaptability to various climates and habitats has facilitated their establishment and spread.
Asian hornets alter ecosystems by reducing populations of native pollinators, which disrupts pollination networks and affects plant reproduction. The decline in pollinators can lead to reduced seed and fruit production, impacting food sources for wildlife and humans. Their predation on honeybees also threatens beekeeping, which is vital for crop pollination and honey production.
Control strategies for Asian hornets include monitoring programs to detect and track their spread, and nest destruction to prevent colony establishment. Trapping and baiting techniques are used to capture hornets, and research is ongoing to develop biological control methods. Public awareness campaigns aim to educate people about identifying and reporting Asian hornets and minimizing their impact.
Preventive measures include stricter regulations on the transport of goods that may harbor hornets and promoting practices to protect pollinators. Beekeepers are advised to enhance hive defenses and monitor for hornet activity. Restoration efforts focus on supporting native pollinator populations through habitat improvement and planting pollinator-friendly vegetation.
Are invasive species always a human caused problem?
In simple terms, no, not always, but mostly. Humans, as a truly global species, move around the planet with a frequency and speed unmatched by any other organism. This movement facilitates the spread of invasive species, whether intentionally or unintentionally. Examples include the transportation of plants and animals for agriculture, the pet trade, and global shipping practices that inadvertently introduce non-native species to new environments.
However, it's important to recognise that the Earth itself is a dynamic system capable of transporting organisms through natural processes and some organisms have developed dispersal methods to facilitate this. Movements of water, such as ocean currents, can carry marine species across vast distances. Wind can disperse seeds and small organisms far from their place of origin. Even geological processes, such as the shifting of land masses, can contribute to the spread of species over long periods.
While human activities are the primary driver of invasive species spread, these natural mechanisms also play a significant role. Understanding both human and natural contributions to the spread of invasive species is crucial for developing comprehensive strategies to manage and mitigate their impacts on ecosystems and economies.Wind
Air
Wind dispersal, or anemochory (what a great word!), is a common method for the spread of plants and certain small organisms. For example, dandelion seeds have a parachute-like structure called a pappus that allows them to be carried by the wind over long distances. This enables dandelions to colonise new areas rapidly, often outcompeting native vegetation and altering local ecosystems. Similarly, aphids, which are small insects, can be carried by wind to new locations. Once established, they can reproduce rapidly and spread plant diseases, impacting both natural ecosystems and agricultural crops.
Water
Marine species often use ocean currents to travel great distances, sometimes ending up in entirely new regions where they can become invasive. Lionfish, for instance, have larvae that can be carried by ocean currents from their native Indo-Pacific region to the Atlantic. Lionfish are voracious predators that can reduce populations of native fish, disrupt coral reef ecosystems, and alter the balance of marine life. Another example is Sargassum seaweed, which floats on ocean currents and can travel vast distances. Sargassum forms dense mats that can smother coral reefs, seagrass beds, and other marine habitats, impacting native species and commercial fishing.
Animals
Animals can inadvertently transport seeds, spores, and small organisms to new locations, facilitating the spread of invasive species. Birds can carry seeds on their feathers or in their digestive systems, later depositing them in new locations through their droppings. The spread of the invasive plant species Lantana camara in tropical and subtropical regions has been facilitated by birds eating its fruit and dispersing the seeds. Lantana camara forms dense thickets that outcompete native vegetation and alter habitat structures.
Migratory fish, such as salmon, can transport organisms attached to their bodies or in their digestive systems. The spread of Didymo, an invasive freshwater algae, has been linked to the movement of fish and other aquatic animals. Didymo forms thick mats on riverbeds, disrupting ecosystems, reducing biodiversity, and impacting water quality.
Large mammals can transport seeds in their fur or through their droppings. In Australia, the spread of blackberries has been aided by animals like foxes and rabbits that eat the fruit and disperse the seeds. Blackberries can form impenetrable thickets, choking out native plants and altering habitats.
Is humanity an invasive species?
By Jpatokal - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7127535
When examining ecological dominance, we see that invasive species are typically organisms that outcompete native species, spread rapidly, and cause significant ecological and economic harm. Humanity’s spread across the globe mirrors this description.
Our unparalleled adaptability and technological advancements have allowed us to dominate nearly every ecosystem on Earth. Similar to invasive species, humans exploit resources intensively, often to the detriment of native flora and fauna. Through agriculture, urbanisation, deforestation, and industrial activities, we have transformed natural landscapes, leading to habitat loss and species extinction.
Our disruption of ecosystems is profound. Human activities have significantly altered ecosystems, resulting in a drastic loss of biodiversity. Activities such as hunting, deforestation, pollution, and climate change have driven countless species to extinction, paralleling the way invasive species often eradicate native species. Moreover, humans have altered natural processes on a global scale. Climate change, driven by fossil fuel consumption, deforestation, and industrial activities, exemplifies this disruption. This change affects weather patterns, sea levels, and the distribution of species, creating conditions akin to those seen when invasive species disrupt native ecosystems.
Ethically, the notion of anthropocentrism places human needs and desires at the centre of ethical consideration. This viewpoint often justifies the exploitation of nature for human benefit, overlooking the intrinsic value of other species and ecosystems. Considering humanity as an invasive species challenges this by emphasising the interconnectedness and equal value of all life forms. This perspective invites a re-evaluation of our moral responsibilities. Recognising that our actions are causing harm similar to that caused by invasive species may inspire more sustainable and ethical practices. This view aligns with environmental ethics, which advocate for the intrinsic value of all living beings and the health of the planet as a whole.
Adopting the view that humans are an invasive species encourages a holistic understanding of our place in the natural world. It highlights the interconnectedness of all species and the importance of maintaining ecological balance. This perspective can foster a sense of humility and stewardship, urging humanity to live in harmony with nature rather than in domination over it. It emphasizes the need for sustainable living, suggesting that recognising the invasive nature of our actions can lead to greater efforts in conservation, restoration, and sustainable resource use. This aligns with the principles of deep ecology, which advocate for a profound respect for the natural world and a commitment to minimising human impact.
The other way…
Humans living in harmony with nature, particularly through indigenous practices, can act as beneficial keystone species, enhancing biodiversity and ecosystem health. This vision is rooted in a deep understanding and respect for the interconnectedness of all life, fostering a holistic approach to environmental stewardship. Indigenous communities engage in practices like rotational hunting, sustainable agriculture, and controlled burning, which maintain ecological balance and promote biodiversity.
These practices play a crucial role in maintaining ecosystem structure and function. Controlled burns by Indigenous Australians, for example, manage landscapes by promoting fire-adapted species and preventing larger wildfires. Traditional agroforestry, as seen in the Amazon, supports diverse habitats and improves soil health by integrating crops with native trees. Rotational hunting and fishing ensure that wildlife populations are not overexploited, allowing ecosystems to thrive. Sacred groves protected by indigenous cultures serve as biodiversity hotspots and refuges for various species.
In contrast to the disruptive nature of invasive species, these sustainable practices enhance ecosystem health and biodiversity. By learning from and integrating indigenous practices, modern societies can transform food and farming systems to be more sustainable and harmonious with nature. This knowledge can lead to agricultural methods that improve soil health, increase biodiversity, and maintain ecological balance, ultimately creating more resilient and sustainable food systems.