Across the globe, fragile ecosystems are threatened by the arrival of invasive species – aggressive, adaptable animals from overseas, who quickly dominate their new surroundings
History has done the dodo a great disservice. A large, flightless bird that once inhabited the island of Mauritius, the dodo became the poster child of extinction when it was swiftly wiped out by Dutch sailors who arrived on the island in the 17th century searching for food. Clumsy and comical, the dodo lacked the survival instinct to even be afraid of humans, and willingly plodded towards its own demise. But why would it have been afraid? When animals evolve, they do so in response to their surroundings, and pre-inhabited Mauritius was an avian paradise, with plenty of fruit on the forest floors and no large mammals to prey on them. It made sense for the dodo to ditch costly adaptations such as defences or flight. But it meant that when invaders from outside Mauritius’ natural ecosystem arrived, the dodo was woefully unprepared for survival. This is a scenario that is repeating itself all across the globe, as human activity has made it easy for competitive species to hitch a ride to new climes. It doesn’t matter if they’re stowaways, escaped pets or have been introduced deliberately for farming or cultural reasons. The end result is always the same: a large proportion of the area’s native wildlife going the way of the dodo.
Eating fish out of their homes
Genetic research suggests the majority of the Atlantic’s lionfish population originate from just a handful of specimens – purportedly six fish that escaped from a Miami aquarium amidst the chaos of Hurricane Andrew in 1992. That was all that was needed for this prolific and aggressive breeder to take a stranglehold on the region’s already frail coral reef ecosystems. A single female can lay as many as 2 million eggs in a single year and with no natural predators, the lionfish population is expanding at an unsustainable rate. As many as 1,000 fish have been recorded in a single acre in some areas. This gluttonous fish will feast on practically anything that will fit in its mouth – it’s been recorded making a dinner out of over 50 different species. Capable of munching 20 small fish in just half an hour, the lionfish outcompetes the waters’ native predators and deprives the reef of species that keep algae levels in check.
Multiplying like rabbits
“The introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting.” So said an English settler named Thomas Austin, who released 24 wild European rabbits onto his Victoria estate in 1859. He should have been a little quicker on the draw. The escapees quickly multiplied like, well, rabbits, and are now widespread across Australia, where their destructive habits are blamed for directly or indirectly causing the extinction of around an eighth of all native mammal species. Their appetite for native plants also causes serious soil erosion problems, as it leaves the top layer, which is rich with vital organic matter and organisms, exposed to the elements. The British should have known better, for they themselves are a victim of this relentless invasive species – it was introduced onto the island by the Romans 2,000 years ago.
The out-of-control pest
In an attempt to curb fire ant numbers, American researchers are pondering whether to introduce its natural enemies from South America. Before they do that, they would do well to consider the precautionary tale of the cane toad. This highly toxic toad was introduced to Australia in the 1930s to control the numbers of local grub beetles, whose larvae destroy the roots of sugar cane crops. In the process, Australia ended up with an even bigger pest on their hands. Like most invasive species, cane toads multiply rapidly and there are no predators to keep their population in check. Their numbers are now so high that for some commuters, running over dozens of cane toads is just part of the daily grind.
The imported menace
The fire ant is pretty much the poster child of a successful invasive species. They’re capable of surviving on just shelter and moisture for weeks – a good quality to have if you’re planning to hitch a ride on a ship. They’re adaptable, capable of building mounds out of almost any kind of soil. And they’re extremely aggressive; anything that roams too close to the nest is swarmed, stung and killed. The fire ant is a huge agricultural menace; not only are their mounds many and unsightly, but they also destroy crops by chewing on saplings and flower buds, and infest and damage electrical equipment. They attack in such numbers and with such ferocity that they are capable of killing or blinding cattle and other domesticated animals. They’ve claimed a few human scalps, too.
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