Threats to biological diversity
3: Exotic Species
Vanessa Couldridge &
Sam Hopkins
Biodiversity & Conservation Biology
Department
Available at http://planet.uwc.ac.za/nisl
Introduction
 The Invasion Biology course discusses exotic
species in detail.
 Rather than repeat everything, the following
examples of invasive species have been selected
for discussion:

Rinderpest

The black rat (Rattus rattus)

The toad/platanna – Xenopus laevis

Chestnut blight
 Viral disease that affects
primarily cattle (also
known as cattle plague)
http://www.virology.net
Rinderpest
 All cloven-hoofed wild and
domestic are animals susceptible to the disease
 Belongs to the genus Morbillivirus
 Affects gastrointestinal and respiratory systems
 Highly contagious and usually fatal; it can wipe
out entire populations
 Death occurs 6-12 days after the first symptoms
Rinderpest: Introduction to Africa
 Introduced to Africa from Asia in 1887
 Disease was present in Indian cattle imported to
the east coast of Africa to feed the Italian army,
which was invading Ethiopia at the time
 Quickly spread to local cattle and wildlife
populations
 From there the disease swept across eastern and
southern Africa, with devastating consequences
 Within 10 years it had reached South Africa
Rinderpest: Spread in Africa
 This map shows
the spread of the
disease across
the African
continent
 The fauna and
flora of Africa
south of the
Sahara changed
completely as a
result
Rinderpest: Plague of 1890s
 Millions of animals died, both wild and domestic
http://www.Aleffgroup.com
 Reports indicate more than 90% of cattle and
wildebeest were wiped out
Rinderpest: Devastation Caused
 Wildlife killed by rinderpest included wildebeest,
buffalo, giraffe, warthog, eland, kudu, and other
buck species
 Predators also suffered as their prey species
disappeared; lions reportedly became maneaters
 Pastoralists depending on cattle for their
livelihood faced severe hardship and death
 Ox-wagon transport was brought to a standstill
 Loss of grazers transformed the landscape
Rinderpest: Control
 The disease was eventually brought under
control through early attempts at vaccination and
natural immunity among surviving animals
 In the early 1960s a more reliable vaccine was
developed and between 1962 and 1976 there was
a large-scale attempt to eradicate rinderpest
entirely from Africa through mass vaccination
 This was largely successful – 15 out of 17
countries were freed of the disease
 Outbreaks still occur from time to time, but none
as severe as the original plague of the 1890s
Rinderpest: Recovery
 Vaccination of cattle in the 1960s eliminated
rinderpest from wildlife populations, as cattle
could no longer act as a reservoir for the disease
http://geoimages.berkeley.edu
 Wildebeest numbers in the Serengeti increased
by about six-fold over a period of 15 years;
Buffalo numbers also increased dramatically
Rinderpest: Landscape Change
1980
http://www.circa.gbif.net/Public/irc/gbif/pr/library?!=/
science_symposia/2006/mduma_ppt/_EN_1.0_&a=d
 This had an impact on the environment by
changing grassland into woodland – an increase
in grazers eliminated the fuel for fires that
control tree growth. Fires are now less frequent
and do not burn as hot
2003
Rinderpest and Canine Distemper
 Ironically, it has been suggested that eradication
of rinderpest has led to an increase in canine
distemper among lions
http://www.eecs.umich.edu
 Lions feeding on wildebeest infected with
rinderpest may have gained immunity to canine
distemper, since the two
viruses are very similar
to each other
(both Morbilliviruses)
The Rat1
 The Black Rat (Rattus rattus) was originally from
Asia
 It made its way to the near East in Roman time
 It was in Europe in the 8th century
 From Europe it had a boat ticket to the rest of the
world
 Rats are nocturnal
 Rats are omnivorous
 They are good breeders
The Rat and the plague2
 The rat and a number of
other rodents are largely
responsible for out
breaks of plague
through history
 Humans as carriers of
rats also participated in
the spread of the
disease
 Often the rats would
then infect native
rodents with the disease
History of the Plague
 An early example is the plague of Justintian 3
 544, The first great plague 4
 1348, Black Death 5
 1665, Great Plague 6
 1899, Plague in South Africa 7
 Recent plague – 2005/ 2006 DRC 8,9
Other effects of rat invasion –
Lundy Puffins 10, 11
 Lundy island is off the coast of
North Devon, UK
 Rats reached the island 200
years ago
 Rat numbers reached 40,000
 Extermination started in 2003
 Puffin and Manx Shearwater
numbers had declined
 Now rats gone, hopefully bird
numbers will increase
Other effects of rat invasion –
Pacific Islands 12,13
 Reached Pacific Islands in the 17th century
 Now established on 28 groups of islands
 Eat native snails, beetles, spiders, moths, stick insects, and
fruit, eggs and young of birds
 Largest threat to the Rarotonga flycatcher
 Other Island birds affected
 Sooty terns, Seychelles
 Bonin Petrels, Hawaii
 Galapagos dark-rumped petrels Galapagos islands
 White tailed tropic birds Bermuda
The Toad –
Xenopus laevis 14
 Xenopus laevis is the
common platanna in
Southern Africa
 It is mainly aquatic
 Females reach 130 mm
 Eats insects, small fish,
young and larvae of its
own species or other
species of frogs
 Adults can breed more
than once per season
The Toad –
Xenopus laevis 14
 Xenopus laevis is found about the world owing to
 Lab animals
 Pet trade
 Pregnancy tests
 These animals escape and can form viable populations
 Now found in USA, Chile, Mexico, France, Indonesia and the UK
 These frogs are a great invader owing to
 Good in disturbed environments
 Has a varied diet
 High reproductive rate
 High salt tolerance
 Disease resistant
 Can move overland or through rivers and streams
The Toad –
Xenopus laevis 14
 Xenopus laevis are a
problem because they
 Predate upon and
compete with native
species
 Are toxic to predators
 Make water turbid
The Toad –
Xenopus laevis
 Seen in Southern California
 X. laevis has been present
since the 1960s
 Preys on the Tide Water Goby
 Preys on the Endangered
Red-legged frog
 Also managed to establish parasites that need alternate
hosts 15
 In South Wales, Xenopus were found to have a very varied
diet ranging from zooplankton to bank voles to Xenopus
eggs 16
The Toad –
Xenopus laevis 17
 In South Africa X. laevis is an invasive
 Animals are moved out of their natural range by
fisherman
 Animals make use of the habitat disturbed by
humans
 Have hybridized with Xenopus gilli
Concluding Remarks
 The selected examples demostrate the damage
that invasive species can do to both the natural
environment and human interests.
 For more information on invasive species see the
Invasion Biology course.
References for the Rat and the Toad
1.
Wikipedia contributors, Black Rat, [accessed 2006 July 30] Wikipedia, The free Encyclopaedia, Available
from:En.wikipedia.org/wiki/Black Rat
2.
Gross, L. (1995). How the plague bacillus and its transmission through fleas were discovered: Reminiscences from my years at
the Pasteur Institute in Paris. Proceedings of the National Academy of Science 92: 7690-7611.
3.
Dols, M. (1974) Plague in Early Islamic History Journal of the American Oriental Society 94:371-383
4.
Maddicott, J. R.(1997) Plague in Seventh -Century England. The past and present society
5.
6.
Davis, D. The Scarcity of rats and the black death: an ecological history, Journal of Interdisciplinary history 16: 455-470
Storey of the Plague,(2006) channel 4 [accessed July 30th 2006]. Found at
http://www.channel4.com/history/microsites/H/history/plague/experts.html
7.
May, J. M. (1952). Map of the world distribution of plague. Geographical review 42:628-630.
8.
9.
BBC news (2005) DR Congo plague outbreak spreads [accessed July 30th 2006] news.bbc.co.uk/1/hi/world/africa/4290783.stm
the world health organization (2006). Plague in the DRC. [accessed July 30th 2006]
www.who.int/csr/don/2006_06_14/en/index.html
Lundy shore office [accessed July 30th 2006] http://www.lundy_ island.co.uk
10.
11.
BBC news (2005) Lundy Rats. [accessed 30th July 2006]
www.bbc.co.uk/devon/content/articles/2005/06/08/lundy_rats_feature.shtml)
12.
Atkinson, I. A. E and Atkinson, T. J. (2000) Land vertebrates as invasive species on islands served by the south pacific regional
ENVIRONMENT PROGRAMME. In: Invasive species in the pacific: A Technical review and draft regional strategy. South Pacific
regional environment program Samoa: 19-84
13.
G. McCormack. (2005). The Status of Cook Island Birds 1996, Cook Island Biodiversity and natural heritage
http://cookislands.bishopmuseum.org/showarcticle.asp?id=7
14.
Measy, J. (2004). Global Invasive species database Xenopus laevis. [accessed 30th July 2006] Found at
http://www.issg.org/database/species/ecology.asp?si=ISO&fr=1&sts=sss
15.
Lafferty, K. and Page, C. (1997) Predation on the endangered Tide Water Goby, Eucyclobius newberryi, by the introduced African
clawed frog I, Xenopus laevis, with notes on the frogs parasites. Copeia 1997: 589-592.
16.
Measey, G. J. (1998) Diet of feral Xenopus laevis (Daudin) in South Wales, UK. Jnl Zool. 246:287-298
17.
Measy G. J. (2004) Xenopus laevis. In Atlas and red data book of the frogs of South Africa, Lesotho and Swaziland, eds Minter, L.
et al.