PREVENTION IS THE BEST CURE Benjamin Franklin once said An ounce of prevention is worth a pound of cure 4 This wise saying certainly applies to invasive species it is much easier to keep them out than to remove them once they’ve spread It’s also much less expensive One of the best ways to prevent invasions is by teaching gardeners pet owners outdoor enthusiasts and others about ways to keep invasive species from spreading Stronger laws can also keep these species from being transported across state lines or from one country to another In 1995 a virus that causes rabbit calicivirus disease RCD escaped a research laboratory on an island near Australia when flies picked it up and carried it to the mainland The virus spread quickly and the population of rabbits crashed again Recently some endangered small animals have begun to recover thanks to the rabbit decline But only time will tell if this will be a permanent solution Some rabbit populations are already showing signs of resistance to the virus Scientists are studying new deadlier strains of the virus for use in the future Meanwhile the government continues to fight the bunny invasion using poisons traps fences and biocontrols WHAT ARE INVASIVE SPECIES The European rabbit is an example of an invasive species a species that arrives in a new area and causes harm Invasive species can be plants animals fungi or bacteria They may harm the environment other plants or animals or human health Next to habitat loss they are considered the greatest threat to biodiversity in the world Approximately 1 4 trillion dollars are spent globally each year to control invasive species and repair the damage they cause 5 Not every exotic or nonnative species is invasive Many such as farm animals and crop plants are useful to humans People in the United States rely on exotic species such as cattle chickens wheat rice and potatoes for food Others are 8
A female rabbit may have one litter every month used in landscaping or kept as pets Approximately 50,000 exotic species can be found in the United States and of these approximately 4,300 are considered invasive 6 This number is so high because Hawaii has many invasive species Scientists estimate that globally approximately 10 percent of species introduced to a new area will survive and reproduce and only approximately 10 percent of those will become invasive 7 9
It usually takes years sometimes even centuries before an exotic species becomes a problem The speed with which this happens depends on how fast the population can grow Species that produce many young in a short period of time can multiply much more quickly than those that reproduce more slowly Thus fast reproducers such as rabbits are much more likely to become invasive than slow reproducers such as elephants It’s hard to pinpoint exactly what makes an organism become invasive Scientists have proposed several different explanations One of these is known as the enemy-release hypothesis This hypothesis is based on the idea that in an ecosystem nature has evolved to keep itself in balance Predators diseases and competitors keep any one species from multiplying too quickly and taking over However when a species moves to a new ecosystem it may not face such challenges With nothing to impede its growth it can quickly spread and outcompete native species for food and habitat It disrupts the balance of the food web that is already in place harming the native plants and animals that live there 10 SPECIES SPOTLIGHT THE NILE PERCH The Nile perch was introduced to Lake Victoria in Africa in 1962 for commercial fishing This large fish is native to the Ethiopian region It quickly began to dominate the ecosystem in Lake Victoria causing hundreds of native fish species to go extinct 8 It is a voracious predator and also carries parasites that can spread disease to other fish The perch changed the ecosystem in other ways as well A large fishing industry quickly sprang up on the banks of Lake Victoria displacing local people who traditionally fished in the lake This affected both the economy and the environment of the area
However some invasive species do face predation and disease in their new habitats And there must be some reason why only a small percentage of introduced species become invasive The answer lies in the concept of fitness Fitness is the ability of an organism to maintain or increase its numbers in the next generation This ability depends on how well suited an organism is to its environment whether it is good at finding resources defending itself against predators and diseases surviving the climate conditions and so on The fittest organism in an environment is best able to pass on its genes Whatever the reason invasive species are simply more fit than their native competitors NATURAL INVADERS In 1883 a massive volcanic eruption obliterated all life on Krakatoa an island near Java and Sumatra in the Indian Ocean But it didn’t take long for plants and animals to recolonize the island Spiders were the first animals to arrive likely carried on the wind Soon grasses and other plants sprouted from seeds carried by the wind or in the droppings of passing birds Today birds nest and sing in the lush rain forest on Krakatoa Introduced species are most likely to become invasive in habitats that are already disturbed For instance the Nile perch's introduction is blamed for causing approximately 200 native fish species to go extinct in Lake Victoria 9 However the populations of these species had already been shrinking from overfishing pollution erosion and excess nutrients They were not well adapted to these changing conditions The more-adaptable perch may have simply finished them off 11
