Biodiversity Connections

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ALIEN INVASION -Species Spread Across the Globe for the Last 500 Years

Non-native species don't always cause damage in new areas that they colonize. However, if and when they do, they could potentially cause billions of dollars of damage. Invasive species have also been linked to the decline of four in every 10 endangered or threatened species in the United States.

A study in Nature Communications this past Feb shows that species are spreading exponentially outside of their native ranges. From Science:

"A team of researchers from across Europe, Asia, and the United States combed through more than 500 years of records from scientific publications, books, and unpublished works taken from more than 280 countries and islands. The documents revealed the very first sightings of alien species in each region, from squirrels to mosquitoes. Altogether, the scientists found 16,926 records of alien species of plant, mammal, insect, bird, and fish [...]


Then, the team analyzed the speed at which new incursions were taking place, broken down by major taxonomic groups. Since 1800, that speed has increased for all groups, with the absolute number of new species reaching 1.5 sightings per day in 1996. Part of this is inevitably because of better recordkeeping over time, says Mark Hoddle, an entomologist at the University of California (UC), Riverside, who was not involved in the work. But Hoddle, who directs the Center for Invasive Species Research at UC Riverside, adds that the key trends are not surprising.

The introduction of nonnative plants exploded in the 1800s thanks to the growth of globalized trade, and it has remained high ever since. Mammals and fish peaked around 1950. But other groups, including algae, mollusks, and insects rose steeply after 1950, thanks to climate change and the post–World War II wave of global trade. For those plants and animals that can easily stow away in the ballast of ships, there is a strong correlation between the spread of nonnative species and the market value of goods imported into each region."

Biosecurity measures seem to be helping but as Margaret Stanley, an ecologist at the University of Auckland who was not involved in the new analysis, adds,  "The challenge now is to set policies that prevent more inconspicuous nonnative species from becoming established."

In Singapore, the brown anole, Norops sagrei, is one of the recent alien species that sneaked into the country with imported plants [Tan & Lim, 2012]. Native to Cuba, the Bahamas, and some adjacent islands in the Caribbean, the species was recorded for the 1st time in Gardens by the Bay. The authors conclude:

"The possible ecological impact from feral brown anoles in Singapore is unknown. At the time of writing, the species seems to be confined to the Marina Bay area, which is an artificial habitat planted with mostly ornamental vegetation. The anole’s preference of exposed scrubland and gardens should enable it to spread beyond the Marina Bay area. However, this should also prevent the anoles from penetrating dense forest at the Bukit Timah Nature Reserve and Central Catchment Nature Reserve where most of Singapore’s small native lizards with similar habits, such as Aphaniotis fusca and Eutropis rugifera, are locally confined. Its effect on native fauna in Singapore remains to be seen, and is worthy of study. Its interaction with the changeable lizard (Calotes versicolor), another introduced species with similar habitat requirements, would be of particular interest. The anoles provide interesting diurnal activity to the gardens, and can probably be tolerated.

Eradication of these lizards may be an option before they spread further, but it would be difficult considering their small size and great agility. The population can probably be restricted to the Marina Bay area by creating barriers on the landward sides, and ensuring that individuals are not inadvertently transported out among plant debris."


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