As the world becomes more connected, invasive species are spreading further. While these species pose threats to our ecosystems, they arguably pose an even greater threat to our agriculture and food security.
Insect pests such as silverleaf whitefly, Asian gypsy moth, and Khapra beetle, are all ranked as major threats and can have significant and far-reaching impacts on agriculture and forest industries around the world.
Many researchers have looked at individual pests to assess their potential threat to particular countries. But no one has ever looked at the invasive threat from a large number of invasive species on agricultural systems at the global level.
Today we have published a paper in Proceedings of the National Academy of Sciences, which attempts to do this. We assessed almost 1,300 insect pests and fungal pathogens. We looked at where they are currently found, trade between those countries, and which crops in each country are vulnerable to attack from these species.
For each country, we estimated the potential impact of those invasive species on their agricultural industries. The most vulnerable countries are developing nations, with sub-Saharan African countries in particular being the most vulnerable, as you can see in the map below.
We combined a great deal of information to estimate a country’s vulnerability to invasive species, such as the global distribution of invasive species, the direction of trade data between countries, the types and value of crops grown in each country, and the Gross Domestic Product (GDP) of each country.
We assessed each country individually, and identified which of the 1,300 pest species were not currently found there. We then determined whether any of those species are known to have an impact on any of the crops grown in that country.
If a species was known to have an impact, we then looked at which countries that species was found in and if the country in question traded with any of those countries.
If it did, we estimated how likely it is that species could travel to the country in question based on the level of trade (this has been repeatedly shown to be correlated to the number of invasive species in a region).
If a species could arrive at a country, the next question was whether it could establish. To determine how likely it would be for a species to establish, we used a novel method, which uses artificial intelligence to compare the source country with the target country.
The method (called a “self organizing map”) compares the collection of species present in each country to determine how similar the two countries are. The more similar they are, the more likely it is that a species from one country could establish in another. The map is able to simultaneously analyse thousands of species and hundreds of countries, making a global analysis possible.
Once we’d figured out if a species could arrive and establish, we wanted an estimate of potential impact. Economic impact is very difficult to estimate even just for one species in one location and the data was simply not available for us at the global level.
As an alternative, we identified the impact of 140 of our 1,300 species and used this to represent the range of possible impacts. We used this to estimate the impact of all the other species on every crop in every country.
Once we’d done this for every species in every country, we put these together to get an estimate of the total potential impact of all invasive species that could invade a particular country.
We found that invasive species would have the largest potential impact on the US and China. This isn’t surprising: these two countries not only have the largest agricultural economies, but also have the largest trade values.
But they are also huge economies with many other economic sectors, so we wanted to know which countries are most vulnerable to the impact of invasion from these species.
We assumed that a country’s GDP represents how much money a country has available to either prevent species from arriving, or to manage them if they do arrive and establish. By dividing the potential impact of invasive species by a country’s GDP, we could get an estimate of its vulnerability.
The larger the impact of invasive species and the smaller the GDP, the more vulnerable a country is. Sub-Saharan countries such as Malawi, Burundi, Guinea, Mozambique, and Ethiopia were all ranked in the top ten for vulnerability.
This is mainly because these countries tend to have narrow economies that are heavily dependent on agriculture and so are more vulnerable than developed countries with more diverse economies, where agriculture is only one of a large number of industries that contribute to the overall wealth of the country.
As trade volumes continue to increase and more trade connections are made between countries it could be argued that the pressures from invasive species will only intensify. The spread of invasive species is a shared responsibility at the global level, and those countries most vulnerable to these invasions will need the most help in combating them.