The introduction of alien amphibian and reptile species often poses a threat to native ecosystems and can throw food webs out of balance. This is not only harmful to flora and fauna: combating such bio-invasions and their consequences have already cost the global economy more than 16 billion euros, as researchers report. Much of this is accounted for by just two species: the brown tree snake and the North American bullfrog.
As globalization progresses, foreign species are being introduced into foreign ecosystems more and more frequently and quickly via the widely ramified trade and transport routes. Many of these species are able to reproduce freely in their new home because they often lack natural predators, which in turn leads to the extinction of native species and unbalances the ecosystem.
One example is the brown tree snake (Boiga irregularis), which presumably arrived on the western Pacific island of Guam during the Second World War as a result of troop transports and multiplied rapidly there – with a devastating effect on the island’s fauna: within a few years many species of birds and other small animals were gone of the island, which were possible prey animals for the snake, are extinct or endangered. As a result of the widespread extinction of the birds – and thus of important seed dispersers – Guam’s flora is now also threatened.
Adder and bullfrog are expensive
However, the invasion of alien species not only has a significant impact on native animal and plant species: “The economy and human society are also affected – with high financial costs for several economic sectors, impairment of livelihoods and loss of human health and prosperity,” explain Ismael Soto from the University of South Bohemia in the Czech Republic and his colleagues. To assess these impacts, the scientists examined the global costs of amphibian and reptile invasions using data from the InvaCost database, which compiles the economic costs of species invasions by experts.
“Our analysis shows that the total costs for the invasion of reptiles and amphibians between 1986 and 2020 amount to more than 16.5 billion euros. Amphibian invasions accounted for €6.1 billion, reptile invasions for €10.1 billion and invasions affecting both amphibians and reptiles for €0.2 billion,” explains Soto’s colleague Phillip Haubrock. The brown tree snake, together with the North American bullfrog (Lithobates catesbeianus), is responsible for almost 16 billion euros, i.e. 96 to 99 percent of the total costs.
How are the costs incurred?
Whether it is reptiles or amphibians that spread in foreign ecosystems has very different effects on the economic damage. For example, according to the study, 99.7 percent of amphibian costs are related to countering invasions, such as eradicating the introduced species. The economic costs in these cases arise primarily in European countries. The costs caused by reptiles, on the other hand, are mainly due to damage directly caused by the invasions, such as crop losses. 99.6 percent of the costs caused by reptiles arise in the countries of Oceania and the Pacific Islands.
“Our study shows for the first time the costs incurred by herpetofauna worldwide. The damage is very likely much higher than InvaCost can show us. We also assume that the invasion rates will increase,” says Haubrock and pleads for active countermeasures: “The economic costs can be reduced by investing in measures to limit the global transport of invasive amphibians and reptiles and by detecting invasions early – prevention is the key cheaper than healing!”
Source: Senckenberg Research Institute and Natural History Museums, specialist article: Scientific Reports, doi: 10.1038/s41598-022-15079-9