Forget about Space Invaders. One of the biggest threats to biodiversity and food security areInvasive Alien Species...
Invasive Alien Species (IAS for short) are plants, animals, or microorganisms which have moved from where they are naturally found to a new location (hence alien) with the intentional or unintentional help from humans. Generally they are species which display invasive traits such as rapid reproduction, habitat displacement, and lots of flexibility and adaptability in the new location, all of which give them a competitive advantage over the native species.
IAS threaten to disrupt nature’s balance and we, humans, have a lot to lose from their impacts. These range from direct impacts to human health, to losses of ecosystem services, loss of biodiversity, crop damage, and financial costs, all of which are interrelated. Environmental losses caused by introduced pests in the United States, United Kingdom, Australia, South Africa, India and Brazil have been calculated at over US$100 billion per year[1].
How do Invasive Alien Species get in?
There are many ways in which humans – accidentally or not – help to move species from their native ranges to new places. The most common way for species to get around accidentally is by stowing away aboard ships, aeroplanes and other vehicles. Our globalised lifestyle has increased the speed and extent to which this can happen, facilitating the movement of live species alongside people or cargoes over long distances.
Some examples of accidental introductions are fruit flies or other insects hiding in fresh fruit and vegetable shipments, ballast water that contains non-native jellyfish, algae or shellfish, and plant pathogens carried in the soil of plants sold for gardening.
Some species are also spread intentionally, often with the best intentions such as biocontrol of another problematic species, erosion mitigation, for food or ornamental purposes. But with poor risk assessment, some of these alien species turn out to be too competitive in their new home, and they ‘jump the fence’. Cane toads were introduced to Australia with the aim of controlling a sugarcane beetle. Cherry guava was taken to Hawaii as a food source. Japanese knotweed was introduced to the UK as a garden plant. These are three disastrous cases on a list that just keeps getting longer.
These are also cases of malicious introductions. One notorious case was exposure of native North Americans to smallpox-contaminated hospital blankets by British officers in 1763[2], as a mechanism of warfare. Another case, classed as ‘agro-terrorism’, was motivated by social and political reasons: a fungus that causes witches’ broom disease in cacao trees was moved from its native range in the Amazon to the cacao tree plantations 3,000 km east in Brazil in 1989[3], causing the cacao industry to drop to half of its production in about two years. Thirty years later, production still hasn’t recovered to the original pre-witches’ broom levels.
Regardless of how introductions occur, it is indisputable that IAS have a negative impact on native species' biodiversity. An analysis of recent extinctions (since the 16th century), placed IAS as a major contributing cause of 25% of plant extinctions and 33% of animal extinctions[4]. This is likely to be just the tip of the iceberg, as the study is conservative and much of the biodiversity we lose has never been described in the first place.
If losing biodiversity wasn’t enough of a problem on its own, there is an aggravating issue: the decline in biodiversity is a growing threat to food security[5]. Biodiversity supplies many vital ecosystem services, such as creating and maintaining healthy soils, pollinating plants, controlling pests and providing habitat for wildlife and biodiversity makes production systems and livelihoods more resilient to shocks and stresses, including those caused by climate change[6].
But why is the risk to food security so high?
Largely, the risk is high because of the agricultural systems we have in place. Only nine species of plants account for 66% of the world’s crop production[6]. This means that if one of these species fails on a large scale, a famine might loom. And a famine based on the failure of one single crop species because of an invasive alien species of pathogen is exactly what happened in Ireland between 1845 and 1849. Granted, climatic events and political issues were contributing factors, but those issues could also play a role in present times.
There is also the threat of generalist pathogens to plant crops – pathogens that are able to infect and cause damage to multiple species that we grow for food, as is the case ofPhytophthorapalmivora, commonly known as ‘bud-root’ or ‘cacao killer’. This species is believed to be native to Southeast Asia, where plants show some resistance to it and where it is kept somewhat under control when in healthy soils and ecosystems. Unfortunately it was introduced to many tropical countries where it attacks hundreds of host plants. It is clearly damaging to the countries’ economies and social structure, and is also a risk as it removes multiple fruits and vegetables from the tables of all the other (non-tropical) countries that rely on these imports.
There is a risk to animals as well, as experienced with the avian influenza in 2005-2007. In the case of animals, some of the prevention strategies include strict monitoring and even sentinel herds – groups of animals that are more exposed to the pathways of introductions, and are meant to catch a disease first; alerting government agencies to the impending problem.
最后,还有一个大的风险的collapse of natural ecosystems. Apart from focusing on the plants and animals that go on our plates, it is important to recognise the role of all other species that provide essential services. Bees and other insects are essential for plant pollination; worms and microbes are essential to keep a healthy soil; and all other ecosystems, including forests, grasslands, and mangroves provide much needed climatic stability for the whole planet.
What can we do about it?
The good news is that there are solutions to the threat to food security. According to the United Nation’s Food and Agriculture Organisation[6], we should be breeding more varieties of each crop, to diversify the genetics of each species, and we should be focusing on native foods. Another big improvement would be to scale back the monocultures, as plant pathogens have a much easier time spreading and taking hold when the crops are uniform and there are few or no barriers to jump.
Preventing IAS should be at the forefront of everyone’s minds. Eradications are sometimes possible, but much more expensive than prevention. For industries and the government, it is important to establish guidelines on treatments of imports (such as fumigation of goods and other quarantine controls at the borders), as well as cooperating with other countries to keep an updated watch-list of potential threats. Farmers must be educated on the identification of IAS and what actions to take if they are detected. For the general population, actions can be as simple as cleaning the soles of your shoes and your luggage before you travel, washing your car if going between different dirt tracks or national parks; and signing up for ‘citizen science’ programs.
最后,它is worth mentioning that everything is connected. Food security is an issue with many sides to it, IAS being one of them – we must not forget it is also a matter of habitat conservation, reducing our footprint, and stopping or reverting climate change. It is not one thing or another that will make it or break it. It is, rather, keeping our planet with its web of connections functioning tightly and well that will allow us to feed 10 billion people by the year 2050-2060.
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