Threats to biological diversity 3: Exotic Species
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Lecturer: James Reeler
Material by: Sam Hopkins & Vanessa Couldridge
BCB 341: Principles of Conservation Biology
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Invasion by alien species can have a significant impact on biodiversity
Usually there are few predatory species/diseases for successful invaders (competitive advantage)
Exacerbated by habitat destruction/disturbance Possibly exacerbated by climate shifts – expansion into
new suitable ranges Primary contemporary cause – humans
Deliberate (plants/animals with economic/aesthetic uses)
Accidental – “piggybacking” on other species
INTRODUCTIONINTRODUCTION
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Not all species that are transported to new areas become invasive.
There are several characteristics of good invaders:
High reproductive rate (quickly build up a large population under favourable conditions)
Generalist species (variable diet, no strong habitat requirements)
Good dispersers (can rapidly spread to new areas & find suitable habitats)
INVASION – WHO?INVASION – WHO?
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Certain areas are more vulnerable to invasion Disturbed areas/early succession
Tend to have unexploited resources/empty niches
Little competition Remote islands with low diversity
Simple food webs/empty niche space Remote islands/fragments with no predators
Often naive prey (included plants poorly adapted to herbivory
INVASION – WHERE?INVASION – WHERE?
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Generally follows three stages: 1. Usually start with a few individuals
High initial likelihood of population extinction Initial establishment phase – growing
population, little size expansion 2. Spreads from initial site and increases range
(expansion phase) 3. Fills all available habitat and enters saturation
phase.
INVASION – HOW?INVASION – HOW?
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The following examples of invasive species have been selected for discussion: Rinderpest The black rat (Rattus rattus) The toad/platanna – Xenopus laevis Chestnut blight
CASE STUDIESCASE STUDIES
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Viral disease that affects primarily cattle (also known as cattle plague)
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
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RINDERPESTRINDERPEST
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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: INTRODUCTION TO RINDERPEST: INTRODUCTION TO AFRICAAFRICA
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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: SPREAD IN AFRICARINDERPEST: SPREAD IN AFRICA
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Millions of animals died, both wild and domestic Reports indicate more than 90% of cattle and
wildebeest were wiped out
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RINDERPEST: PLAGUE OF 1890SRINDERPEST: PLAGUE OF 1890S
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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 man-eaters
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: DEVASTATION RINDERPEST: DEVASTATION CAUSEDCAUSED
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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: CONTROLRINDERPEST: CONTROL
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Vaccination of cattle in the 1960s eliminated rinderpest from wildlife populations, as cattle could no longer act as a reservoir for the disease
Wildebeest numbers in the Serengeti increased by about six-fold over a period of 15 years; Buffalo numbers also increased dramatically
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RINDERPEST: RECOVERYRINDERPEST: RECOVERY
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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
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RINDERPEST: LANDSCAPE CHANGERINDERPEST: LANDSCAPE CHANGE
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Ironically, it has been suggested that eradication of rinderpest has led to an increase in canine distemper among lions
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)
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RINDERPEST AND CANINE RINDERPEST AND CANINE DISTEMPERDISTEMPER
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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 RATTHE RAT11
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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
THE RAT AND THE PLAGUETHE RAT AND THE PLAGUE22
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An early example is the plague of Justinian 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
HISTORY OF THE PLAGUEHISTORY OF THE PLAGUE
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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 – OTHER EFFECTS OF RAT INVASION – LUNDY PUFFINS LUNDY PUFFINS 10, 1110, 11
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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
OTHER EFFECTS OF RAT INVASION – OTHER EFFECTS OF RAT INVASION – PACIFIC ISLANDS PACIFIC ISLANDS 12,1312,13
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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 –THE TOAD –XENOPUS LAEVIS XENOPUS LAEVIS 1414
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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 –THE TOAD –XENOPUS LAEVIS XENOPUS LAEVIS 1414
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Xenopus laevis are a problem because they Predate upon and
compete with native species
Are toxic to predators Make water turbid
THE TOAD –THE TOAD –XENOPUS LAEVIS XENOPUS LAEVIS 1414
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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 –THE TOAD –XENOPUS LAEVISXENOPUS LAEVIS
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In South Africa X. laevis is an invasive Animals are moved out of their natural range by
fisherman Animals make use of habitats disturbed by
humans Have hybridized with Xenopus gilli
THE TOAD –THE TOAD –XENOPUS LAEVIS XENOPUS LAEVIS 1717
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Maine to Georgia and west to Ohio and Tennessee. (Braun, 1950)
Commonly made up 25% or more of mixed stands
Formed pure stands on many dry Appalachian ridgetops and near densely populated areas.
Map of Historical Range of Castanea dentata (Saucier, 1973)
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Common on midslopes and other moderately dry soils
Shared moist meso-phytic soils with many other species
Tap root 4 to 5 ft down
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Mature chestnuts could be 600 years old and average up to five feet in diameter and 100 feet tall
Many specimens of 8 to 10 feet in diameter were recorded
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Wildlife depended on the abundant crop of chestnuts
Many species of insects fed on the leaves, flowers, and nuts
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Throughout much of the range chestnut had the most timber volume of any species
It was half the standing timber volume of CT
Was the major source of tannin for leather pro-duction (6-11 % tannin content)
Chestnuts
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Fast growing -reached half ultimate height by 20th year
Resistant to decay
Straight and tall - often branch free for 50 feet
Only white pine & tulip poplar could grow taller
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Posts & railroad ties
Telephone poles (65 feet)
Construction
Fuel
Fine furniture & musical instruments
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Scientific forest management in the US was just getting started when the country lost its most important hard wood species (Smith, 2000)
Foresters had begun to develop comprehensive plans for intensive management
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Near densely populated areas Chestnut often formed nearly complete stands
due to rapid growth from stump sprouts
repeated coppicing for fuelwood
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Experts estimate that American Chestnut represented half the commercial value of all Eastern North American hardwoods
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“… “… the most valuable and usable tree that the most valuable and usable tree that ever grew in the Eastern United States.”ever grew in the Eastern United States.”
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In 1904, Herman Merkel, a forester at the New York Zoological Garden, found odd cankers on American chestnut trees in the park
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"rapid & sudden death of many branches stems & trees"
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American Chestnut produces a sweet but small nut
Chinese chestnut produces a large but generally tasteless nut
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Thomas Jefferson imported European or Spanish chestnut
(Castanea sativa) grafted it onto native root stocks at Monticello.
In 1876, a nurseryman in Flushing, NY, imported the Japanese chestnut (C. crenata). More were brought over in 1882 and 1886.
Chinese chestnut (C. Molissima) was brought across from Ichang in 1900. to hybridize for ornamentals and nut
production
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Ascomycete
Produces both conidia & ascospores
Pycnidia stromata break through the lenticels and produce conidia and perithecia producing ascospores are formed
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Animals and insects
Ascospores are shot into the air after rain storms in the fall
Rain (conidia)
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Infects trunk and branches Only above ground parts
of trees
active growth & sporulation
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Enters through fissures or wounds in the bark
Grows in and under the bark, girdling the cambium.
Kill the tree above the point of infection.
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Causes swollen or sunken orange-colored cankers on the limbs and trunks of the chestnut trees.
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The leaves above the point of infection die, followed by the limbs.
Within two to ten years the entire tree is dead.
Not uncommon to find many cankers on one tree
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The fungus has girdled the tree and is producing yellow conidia asexual spores
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Like most cankers - fairly specific host range
Serious pathogen: American & European (infects Japanese and Chinese much less)
Moderate pathogen: Chinquapin & Live Oak
Can also be found infecting/living on numerous oak species in the US
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Aggressive attempts to halt the spread of the blight were made by PA and NY removed chestnut over
a large area to halt southward spread
In 1911-1913, the U.S. Congress appropriated special funds to enable foresters to study and control the blight
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Horticulturalists, found a blight-free area in Pennsylvania and quickly imported trees to form an experiment station
transported the blight and created a new epicenter
Accelerated spread in PA
Cuts in funding for Chestnut blight research:
With the onset of World War I in 1914
The evident futility of control efforts
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By 1926, fungus reported throughout native range
By 1940, virtually all (an estimated 4 billion) were dead or infected with the blight
Chestnut was the dominant wood processed at PA sawmills in the early 1920s, salvage logging to make use of the dead
and dying trees
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“…a tragic loss, one of the worst natural calamities ever experienced by this nation”
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Chestnut in Southern range was first affected by Phytophtera cinnamomum
Now affecting hybrids
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In 1974, the Oriental Chestnut Gall Wasp (Dryocosmus kuriphilus) was brought to the US
Female lays eggs in chestnut vegetative buds
Galls suppress shoot elongation and reduce fruiting
Heavy infestations can kill the trees (afflicts both American and Chinese chestnuts at the southern end of their ranges)
Threatening complete extinction
(Anagnostakis, 1994)
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The fungus was later introduced into Europe (for tree breeding) from America
Moved through Europe killing European Chestnut
However, it was observed that many trees, while infected and full of cankers, did not die
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Instead of sunken diffuse cankers, surviving European chestnuts had swollen cankers with evidence of "healing" along the margins.
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Many forest pathologists began working on this healing canker
Speculation that: European Chestnut was less
susceptible That the fungus had mutated That it was a different fungus
altogether
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Noticed that a different colored fungus was recovered from "healing cankers"
Instead of the typical orange colored Cryphonectria parasitica fungus, a white-colored fungus was found. White fungus was slower growing and produced fewer
spores When you "sprayed" the white fungus on a "killing
canker" the "killing canker" became a "healing canker" (Europe)
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Determined that the white hypovirulent strains had become infected with a simple dsRNA virus
This virus was making the fungus "sick“
A slower fungus allowed the tree to respond to a point where the tree could survive infection
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Grente reported in 1965 that ‘hypovirulent’ strains from Italy did not kill chestnut trees
Began a program of active intervention when blight was found in France blight strains with dsRNA passed
hypovirulence to lethal strains
Treatment of new cankers as they formed resulted in a successful ‘biological therapy’ of the disease. treat every canker for several years
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For a number of reasons biological control of chestnut blight does not work as well in the US
Different mating types of the fungus Lack of chestnut to support conversion of
the fungus by the virus
The many different types of virus in the United States
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Hypovirulent strains were found in the United States Most notably in Michigan
Successful because: Few mating types High number of Chestnut Isolated from the native range
Less diversity of pathogen in MI so that hypovirulence can transfer more readily
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The transmission of hypovirulence from strain to strain of the fungus is restricted by a genetic system of vegetative incompatibility
Six loci, each with two alleles in a system of heterogenic incompatibility which keep the strains of the fungus from fusing and passing hypovirulence (Huber and Milgroom)
Virus transfer is restricted when there are different alleles at the vegetative incompatibility loci
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Reduced to a short lived sprouting understory tree
Fungus can not survive below the ground. roots continue to live and they send up
stump sprouts.
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Stump sprouts grow until infected the stump re-sprouts again
Little chance for resistance to evolve sprouts typically killed before they
become sexually mature sexual reproduction rare
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Largest living (>3 ft dbh) about 20 miles east of La Crosse, WI.
10 chestnuts planted in 1885 Seeds propagated around 50
acres and more than 3000 trees Trees were blight free due to
isolation until a canker was found in 1986
Now over 1600 cankers are present on 530 trees.
Virus was introduced in 1992 – not successful
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Approaches:
Hypovirulent strains
Asian blight resistance
Natural resistance Forest management practices
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Combination of the four approaches can bring the chestnut back Individual or group selection openings-
an integrated management system using grafted trees, inoculating them with hypovirulent strains, and controlling hardwood competition
Timber production- backcross approaches
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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.
CONCLUDING REMARKSCONCLUDING REMARKS
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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.
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REFERENCES FOR THE RAT AND THE TOADREFERENCES FOR THE RAT AND THE TOAD