- Over 3,500 harmful invasive alien species have been introduced into regions and biomes around the world by human activities, says an assessment report.
- The global economic cost of invasive alien species, that negatively impact nature and people, exceeded $423 billion annually in 2019. Costs have at least quadrupled every decade since 1970.
- About 60% of species extinctions are attributable to invasive alien species either solely, or in combination with other drivers.
- About 90% of documented global extinctions of native species, attributed mainly to invasive alien species, have occurred on islands, especially remote islands.
The spread of invasive species is one of the five major threats to biodiversity and ecosystem services. These animals, plants, fungi and microorganisms, that establish themselves in an environment outside their natural habitat where they can have negative impacts on native biodiversity, usually do not receive as much attention as the other threats of climate change, pollution, sea and land-use change.
A new report by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), highlighting the global threat posed by invasive alien species, reveals that multiple anthropogenic activities have introduced more than 37,000 alien species to regions and biomes around the world, with the number rising at 200 new alien species every year. Among the established alien species, more than 3,500 are harmful invasive alien species (IAS) with negative impacts on nature and people. More than 2300 invasive alien species are found on lands of indigenous peoples across all regions of earth. About 60% of species extinctions are attributable to invasive alien species either solely, or in combination with other drivers.
The assessment follows a decision at a previous IPBES plenary about the need for a global assessment on invasive alien species. Prepared by representatives of the 143 member states of IPBES, an independent body focussed on sustainable management biodiversity, the first comprehensive global report on invasive alien species and their control says the global economic cost of invasive alien species exceeded $423 billion annually in 2019, with costs having at least quadrupled every decade since 1970.
Bengaluru-based ecologist and evolutionary biologist Alok Bang called the revelations in the assessment report “staggering” and one that highlights the need to take the threat of bioinvasions seriously. He said the ecological impacts of invasive alien species are known in scientific circles but when the impacts are assigned economic values, they appear more relevant. “The economic value in the report is only the tip of the iceberg because it is impossible to quantify many ecological impacts of invasive alien species like the loss of native species,” he said.
A conservative estimate from India suggests that over the last 60 years, invasive species have cost the Indian economy $127 billion. A pan-India monitoring of invasive plants for the last 16 years suggests that one-time control of invasive plants across India would necessitate $13.5 billion, with uncertain outcomes.
Researchers call the IPBES report the most comprehensive global assessment on biological invasions and one that “draws upon scientific literature, gray literature as well as indigenous and local knowledge from across the world, regarding the pathways and processes of alien species invasions, their drivers, and their impacts,” noted Ankila Hiremath, adjunct senior faculty at Ashoka Trust for Research in Ecology and the Environment (ATREE) and a lead author of the report. It also reviews and analyses existing efforts, and explores future options, providing the policy makers the best possible evidence, tools and information to develop policies for management.
Impact on island nations, indigenous communities
Despite increasing awareness, most countries lack a national legislation or regulations directed specifically towards the prevention and control of invasive alien species with nearly half of all countries not investing enough in their management. For a country that boasts of multiple biodiversity hotspots and endemism, it is vital for India to have dedicated policies, an integrated governance system and a strong biosecurity system in place, according to experts. One of the authors of the chapter on policies and governance in the IPBES report, Ninad Mungi informed Mongabay-India that the existing policy instruments have indirect guidelines, policies and laws that can be contextually used. “There is an urgent need to draft dedicated policies on the subject with updated knowledge and scientific findings,” he said.
The negative impacts of bioinvasions are far-reaching, affecting the economy, food security, water security and human health. The report suggests that more than 90% of the economic costs assessed are related to impacts on nature’s contributions to people and the quality of life. Indigenous people are disproportionately affected by this since they are more directly dependent on nature and natural resources given the impacts of invasive species on native species and natural ecosystems.
Hiremath cited the example of the widely spread South American shrub Lantana camara and its impact on the livelihoods and wellbeing of the Soliga Adivasis in Karnataka. “Lantana has been shown to affect the regeneration of amla, an important non-timber forest produce that people depend on for their livelihoods,” she said.
Moreover, Lantana’s dense understory has replaced the open grassy understory of the forest exposing the forest dependent communities to the hazard of increased encounters with large animals like elephants. Some invasive alien species like Lantana also disrupt the traditional and cultural way of living of indigenous peoples, for instance, by blocking easy access to their sacred sites.
At the same time, certain established invasive alien species have become a valued part of the socio-ecological system of indigenous peoples and local communities that management of it is a socio-economic issue faced by managers, according to K.V. Sankaran, former director, Kerala Forest Research Institute and coordinating lead author, IPBES. “A good example is Prosopis juliflora, an invasive alien tree. Charcoal made from the tree is a source of income for local communities and hence attempts at managing the species have been problematic,” he said.
India has made progress in the identification and detection of invasive alien plants with Lantana, thanks to its proliferation and large-scale negative impacts, including economic loss, leading the country’s efforts in mitigation strategies. The same cannot be said about identifying invasive alien invertebrates, fungi and other microorganisms and marine organisms which is an impediment in designing biosecurity systems.
The report also highlights that 90% of documented global extinctions attributed mainly to invasive alien species have occurred on islands, especially remote islands with high levels of endemism, largely attributable to chance colonisations and diversification over millennia. Hiremath explained that these island species are often sheltered from certain elements of biota like predators or certain diseases and this combination of endemicity and their relatively “sheltered” existence makes them particularly vulnerable.
Globalisation and tourism are integrated into island economies, making it difficult to prevent invasion, said Sankaran. “The smaller size of islands, the smaller population of individual species as well as their isolation create evolutionary distinctness, species impoverishment and taxonomic disharmony which make islands more vulnerable to bioinvasions,” he said. While it is not yet known which regions in India are the most susceptible to invasion, Sankaran said that since the invasive alien plants in India have their origin in tropical America, a humid tropical climate is conducive for enhanced invasion by alien plants in India.
Invaders can enable more invasions if not handled adequately
Emphasising the need for effective strategies to manage invasive alien species, the assessment notes that interactions among invasive alien species can enable further biological invasions. Mungi said that we are increasingly witnessing what is globally called the “invasional meltdown hypothesis” where various invader-invader interactions facilitate further invasions. Sankaran explained the ways by which it happen. “An invasive alien species can positively interact with other invasive alien species facilitating their spread or promote the establishment of other invasive alien species by modifying the ecosystem. The biological control to manage one established invasive alien species can lead to the establishment of another or certain carrier species can facilitate the transportation of alien species to new regions,” he said.
A study done in dry forests of Kanha Tiger Reserve found that Lantana camara reduced the growth and diversity of native nutritious plants. This space left behind by them is utilised by alien and native weedy species, which cumulatively further depletes the native plant diversity which has a significant impact on native herbivores and subsequently, the native carnivores.
There are isolated programmes to manage bioinvasions in India but none that are foolproof, said Sankaran.
He said that apart from an exclusive national policy framework to deal with invasive alien species and a single nodal agency and an integrated governance system to implement the prescribed regulations, we need to update the biosecurity regulations and infrastructure, streamline the quarantine controls and surveillance systems, strengthen domestic quarantine regulations and amp up our capacity to deal with modern tools and techniques in managing biological invasions, among other measures to be taken. He also emphasised on the need to make the public aware of the negative impacts of invasive alien species and engage all stakeholders including indigenous peoples and local communities in its management among some effective management measures to adopt.
Banner image: Indian Bullfrog (Hoplobatrachus tigerinus). The invasive Indian bullfrog, native to the Indian subcontinent, is currently an invasive species in the Andaman archipelago in the Bay of Bengal. The islands are disproportionately impacted by the spread of invasive species. Photo by Raju Kasambe/Wikimedia Commons.