Invasive Alien Species
Climate change, habitat loss, and pollution are environmental challenges defining the 21st century; another less well-known but equally related aspect is the proliferation of invasive alien species. While the migration and ‘invasion’ of species is nothing new, two reports by the European Environment Agency (EEA) turn the spotlight on how alien species are intentionally introduced to new places while many other introductions are unintentional. Ruth Gamano looks at the reasons, the effects and future of species invasions.
Introduced intentionally or accidentally by human activity, invasive alien species are animals, plants, fungi and micro-organisms which cause adverse effects on their new habitat or bio-region; for example, by out-competing or predating native species, which evolved without specific adaptations to cope with them. Once established in their new environment, such species can be extremely difficult or even impossible to eradicate and can lead to the devastation of populations of native species, causing harm economically, environmentally and ecologically.
For these reasons, invasive alien species have been recognized as one of the most serious threats to biodiversity at the global level, second only to habitat loss and destruction (“Status, impacts and trends of alien species that threaten ecosystems, habitats and species”, Convention on Biological Diversity, 2001.
Damage caused by invasive species has been chronicled throughout history. In 77 AD, Pliny the Elder, a learned natural philosopher of the early Roman Empire, wrote in his encyclopaedia Natural History about the rabbit invasion of the Balearic Islands, describing it as such a drastic problem that the help of the Emperor Augustus and the Roman Army was sought to control them. Even then invasive species were not new; some human-initiated introductions are known to date back to Neolithic times, especially around the Mediterranean. Such species as the pheasant, originated from Asia, have been introduced around the world and became integral parts of their adopted habitats to the extent that they seem native today.
“While bringing short-term socio-economic profit, some alien species turn out to be invasive, damaging biodiversity and natural resources in the long-term”
The long history of species introductions to Europe may be responsible for the lower level of awareness about associated problems in comparison to other areas of the globe. The introduction rate of invasive species to Europe is accelerating but insufficient care and concern is shown with regards to this threat. This is gradually changing now and increasing recording and publicity of the associated impacts are raising awareness of the issue, especially in relation to human health, biodiversity and the environment.
Impacts of Invasive Alien Species
The full extent of the threat posed by Invasive Alien Species is becoming better understood thanks to various scientific studies that have been undertaken in recent years. Between 1994 and 2006, the European Commission funded 90 research projects related to, or dealing entirely with the issue, with a total budget of more than €88 million. These projects included ALARM, IMPASSE and DAISIE (Delivering Alien Invasive Species in Europe). DAISIE supports a comprehensive review of the scale of, and ecological and economic impacts caused by, invasive alien species of all types in Europe. Data collected through this project shows that of all alien species in Europe at least 11% are known to have negative ecological impacts and 13% negative economic impacts. Of the 395 European native species listed as critically endangered on the IUCN Red List of Threatened Species, 110 are at risk due to invasive alien species.
Many non-native species are introduced to new areas, therefore being ‘alien’, without being invasive. Sometimes, they fail to adapt sufficiently to their new environment to establish self-sustaining populations and eventually die off. This is true of species such as crocodiles and pythons, some of which have been released or escaped in Europe, but have not become problematic in the long-term. In other cases, species are introduced and inhabit new eco-systems without damaging them. They co-exist with native species without competing with them. The Corsican ‘Red’ deer, which is thought to have been introduced to Corsica by humans in ancient times, is even protected by EU legislation as a valued aspect of the island’s environmental and cultural heritage.
The introduction of alien species can bring enormous economic benefits in certain sec- tors, such as agriculture, animal farming, fishing, wood production, medicine, hunting, and the ornamental plant trade. Alien species can even sometimes offer benefits to the natural environment of their new habitats by being food sources for native species and by replacing previously lost vegetation cover. However, this is misleading since such apparently beneficial effects can still harm the natural balance of eco-systems in the long-term. While bringing short-term socio-economic profit, some alien species turn out to be invasive, damaging biodiversity and natural resources in the long-term. One example is the Red Swamp Crayfish, which brings beneficial fishing opportunities in areas like southern Spain, but also carries the crayfish plague pathogen that can drive native crayfish species populations to extinction.
There are various ways a species can cause harm in its new environment, therefore being invasive rather than simply non-native. The EEA reports identify 14 types of Invasive Alien Species impacts and classify them into 4 groups:
1. Impacts on Biodiversity
Invasive alien species can affect biological diversity at gene, species and eco-system levels.
Competition, predation, hybridization and disease transmission are common and can endanger native species. In isolated eco-systems this is known to affect all levels of local food webs.
2. Impacts on Eco-system Services
Eco-system services are direct and indirect contributions of eco-systems to human well-being, and are classified in four sub-categories:
Provisioning services: products obtained from ecosystems such as water, food, genetic resources, wood, fiber and medicines;
Regulating services: beneficial regulatory effects of ecosystem processes such as climate stability, natural hazard regulation (flood control), water purification, waste management, pollination, and pest control;
Supporting (habitat) services: soil formation and nutrient cycling, providing habitats for migratory species and gene pool viability maintenance;
Cultural services: recreational, religious, spiritual and intellectual enrichment, and other non-material benefits gained from eco-systems.
3. Impacts on Human Health
Invasive alien species, which have negative effects on eco-systems, in turn have negative effects on human well-being through the disruption of these services. Human health can be affected either directly or as vectors of specific diseases. Such problems include skin lesions upon contact with giant hogweed sap, rhino-conjunctivitis and asthma through contact with common ragweed allergenic pollen, and the chikungunya virus spread by the tiger mosquito.
4. Impacts on Economic Activities
Invasive alien species can cause dam- age to infrastructure, landscapes and agriculture. In Australia, Brazil, India, South Africa, the United Kingdom and the United States, related losses have been calculated as approximately $300 billion per year (‘Update on the environmental and economic costs associated with alien-invasive species in the United States’, Ecological Economics Pimentel et al., 2005). This is probably an underestimation, as socio-economic consequences are difficult to quantify in financial terms, and economic and environmental impacts are unknown for many alien species (‘How well do we understand the impacts of alien species on ecosystem services? A pan-European cross-taxa assessment’, Frontiers in Ecology and the Environment, Vilà et al., 2010).
Addressing the Invasion Debt
Global patterns suggest that the numbers of alien species and their impacts will increase (‘Global Biodiversity: Indicators of Recent Declines’, Science, Butchart et al., 2010,). Invasive alien species are likely to cause increased fragmentation, destruction, alteration and replacement of habitats, which will affect even more species and eco-systems. Many past invasions could have been prevented and measures for early detection and rapid responses must be implemented now to help prevent and control future invasions. Species which have already invaded new habitats must be controlled and, where appropriate and possible, eradicated. Long-term species management should be a last resort.
Eradication of invasive alien species is widely viewed as the most effective way to conserve endangered species, with more than 1,000 successful eradications recorded worldwide. The conservation statuses of 11 bird, five mammal, and one amphibian globally threatened species have improved as direct results of such programmes (“Global indicators of biological invasion: species numbers, biodiversity impact and policy responses”, Diversity and Distributions, McGeoch et al., 2010).
This is one of the greatest environmental challenges of modern times, and one which various agencies and authorities are now addressing. In the publication “Our life insurance, our natural capital: an EU bio-diversity strategy to 2020”, the European Commission aims:
By 2020, Invasive Alien Species (IAS) and their pathways are identified and prioritised, priority species are controlled or eradicated, and pathways are managed to prevent the introduction and establishment of new IAS. The EEA has contributed extensively to work in this field, including the technical report “Towards an early warning and information system for invasive alien species threatening biodiversity in Europe”, which assesses the options for a European early warning system, identifying key challenges and presenting estimated costs.
Due to the multiple shared borders, mountain ranges and water courses in Europe, invasive alien species are easily spread between countries. This makes a harmonized pan-European strategy, necessitating legislative frameworks at both regional and local levels, vital to effectively manage them.
Globalization and international trade are also major contributors to the movement of species and are therefore important factors in invasive alien species control. Many species are intentionally moved and traded internationally and other species are transferred accidentally as a consequence of such trade. The EEA reports state that 90% of world trade is carried by sea and by 2018, the world fleet could increase by nearly 25% with volumes nearly doubling compared to 2008. In addition, approximately 650 million people travel internationally every year. Both greatly increase the risk of unintentional species transfers. These conditions need improved coordination between national authorities, including reinforced controls at airports, harbours and other entry points, with resources such as scanners and sniffer dogs, targeted training, and powers of consignment seizure and destruction.
In their 2011 paper “Socioeconomic legacy yields an invasion debt”, Essl et al. coined the term “invasion debt”, highlighting that current patterns and impacts of alien species reflect past activities and migrations rather than current patterns. Many of the most damaging alien species invaded their new habitats many years ago. It will therefore be impossible to judge the effects of current activities until decades in the future.
The boom in biofuels correlates invasive alien species and climate change. In the fight against climate change, fossil fuels are increasingly being replaced by biofuels. The 2009 EU Renewable Energy Directive (RED) endorses a mandatory 10% minimum target for the share of biofuels used in transportation by 2020. Biofuel crops may provide opportunities for alien species to invade new territories, as they are planted on large scales and are usually fast growing and highly competitive species. Apart from deforestation and land change brought about for their production, there is a high risk of such crop species spreading outside their official production areas. This means carrying out risk assessments before selecting biofuel species for specific areas.
Climate change is an environmental phenomenon with varied effects, including changing which species are able and unable to thrive in specific areas. Native species which fail to adapt to the new environmental conditions of their native territory are likely to die out and be replaced by better adapted alien species. Climate change is also expected to affect the distribution and impacts of existing invasive alien species. Many are highly adaptable and are likely to cope better than native species, increasing the likelihood of their dominance. Natural disasters such as floods and fires which destroy or displace native species may also allow new species to replace them.
It will therefore be impossible to judge the effects of current activities until decades in the future.
One problem in dealing with this issue is the lack of globally accepted, reliable indicators of biological invasions. The EEA project, “Streamlining European 2010 Biodiversity Indicators” assesses progress towards halting the loss of biodiversity in Europe by 2010. A response indicator measuring the “Trends in invasive alien species in Europe” was developed as part of this process, and consisted of two elements:
1. Cumulative number of alien species in Europe since 1900
2. Worst invasive alien species threatening biodiversity in Europe
This indicator is considered to be effective, but needs further improvement. A lack of consensus about the definition of invasive species, the lack of reliable data about both native and invasive species, and the variety of species involved and the problems they cause all make establishing reliable indicators difficult. Many projects continue to work on this issue and much more work remains to be done.
Writer: Ruth Gamano is an independent contributor to Revolve. This article appeared in Revolve#9, Fall 2013, pages 10-17