Native species are those that naturally live in an ecosystem, while nonnative species are those introduced intentionally or unintentionally. Most introduced species are beneficial, but some become invasive and threaten native species by outcompeting them without natural predators. One example is African bees introduced to Brazil for honey production that displaced domestic bees. Another major invasive species introduction was rabbits to Australia, which grew to a population of 10 billion by 1920 and damaged native plants and degraded the land. Biological control uses an invasive species' natural enemies for control, but this does not always work as intended, such as with cane toads introduced to control beetles in Australia.

1. CONCEPT OF EXOTICS AND INVASIVES
Rounak Choudhary
M.Sc. (Gold Medalist), UGC-NET & ICAR-ASRB NET Environmental Science, DCB Ornithology, PGD Industrial Safety, Health and Environment

2. • Native species are those species that normally
live and thrive in a particular ecosystem. Other
species that migrate into or are deliberately or
accidentally introduced into an ecosystem are
called nonnative species, also referred to as
invasive, alien, or exotic species.
• Nonnative species can spread rapidly if they
find a new more favorable niche. In their new
niches, these species often do not face the
predators and diseases they faced before, or
they may be able to out-compete some native
species in their new niches.

3. • Some people tend to think of nonnative species as
villains. In fact, most introduced and domesticated
species of crops and animals, such as chickens, cattle,
and fish from around the world, are beneficial to us.
However, some nonnative species can threaten a
community’s native species and cause unintended and
unexpected consequences. In 1957, for example, Brazil
imported wild African bees to help increase honey
production. Instead, the bees displaced domestic
honeybees and reduced the honey supply. Since then,
these nonnative bee species—popularly known as
“killer bees”—have moved northward into Central
America and parts of the southwestern and
southeastern United States. The wild African bees are
not the fearsome killers portrayed in some horror
movies, but they are aggressive and unpredictable.
They have killed thousands of domesticated animals
and an estimated 1,000 people in the western
hemisphere, many of whom were allergic to bee stings.

4. v

5. Remember HIPPCO
• Conservation biologists summarize the most
important causes of premature extinction
using the acronym HIPPCO: Habitat
destruction, degradation, and fragmentation;
Invasive (nonnative) species; Population and
resource use growth (too many people
consuming too many resources); Pollution;
Climate change; and Overexploitation

8. The rise of the rabbit
• One of the most notable species invasions has
been that of the European rabbit in Australia.
It began in 1788, when 11 ships landed at
Botany Bay from Britain, to establish the first
Australian penal colony. On board the “First
Fleet,” along with more than 1,000 people,
including convicts and emigrants, were six
European rabbits, brought along for food.

9. • By the 1840s, rabbits had become a staple
food in Australia, and were contained within
stone enclosures. All this changed in 1859
when a settler, Thomas Austin, imported 12
pairs of European rabbits and released them
on his estate near Geelong in Victoria. Twenty
years later, rabbits had migrated to South
Australia and Queensland, and then in the
next two decades to Western Australia. By
1920, the rabbit population was 10 billion.

10. • Rabbits appear to be innocuous creatures, but
they have wreaked havoc on Australia’s native
species, competing with them for resources such
as grass, herbs, roots, and seeds, and degrading
the land. They become particularly troublesome
during a drought, when they eat anything they
can find in order to stay alive. There have been
several attempts to control the feral population,
from rabbit-proof fences stretching more than
2,000 miles (3,200km) to the more successful
introduction of the myxoma virus and the rabbit
calicivirus, in 1950 and 1995 respectively. The
resulting disease has proved the most effective
way of controlling their numbers and protecting
native species.

11. The art of control
• Successful invasive species are extremely
difficult to control and almost impossible to
eradicate. If the species is a plant, the most
obvious way to remove it is to pull it up or cut
it down, but such methods are highly labor-
intensive, especially over a wide area. The use
of chemicals to destroy invasive species is
often successful, but it can also kill native
species and undermine soil health, with the
added threat of harm to humans.

12. • One frequently used method of control,
known as biological control, or “biocontrol,”
pits an invasive species’ own enemies against
it. In an early success, the cactus moth was
introduced to Australia from South America in
1926 to feed on the prickly pear. This plant
had itself been introduced in the 1770s and
was choking farmland in New South Wales
and Queensland. By the early 1930s, most
prickly pears had been eradicated.

13. • Not all biological controls are effective, and some
measures have had disastrous consequences. For
example, in 1935 cane toads were introduced to
Australia to control the invasive grayback cane beetle,
which was destroying sugar cane fields. The cane toad
had been effective in controlling beetles in Hawaii, so
the assumption was that it would be equally successful
in Australia. However, grayback cane beetles feed
primarily at the top of sugar cane stalks, which is out of
reach for the cane toads. A lack of understanding of the
different environments favored by the two creatures
meant that the cane toad was the wrong choice as a
biological control. By the time the mistake was
realized, the toad had spread throughout Australia,
poisoning any predator species that tried to eat the
toxic amphibian.