Species invasions
鄭先祐(Ayo)
台南大學 環境與生態學院 院長
Japalura@hotmail.com
Contents
 What are the conservation
implications of introduced species?
 What are the impacts of invasions?
 What factors determine whether a
nonnative species becomes invasive?
 How are species introduced?
 How do we manage specie invasions?
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Supplements
 Essay 9.1 maintaining an open mind
on nonnative species
 Essay 9.2 Global exchange
 Box. 9.1 understanding the impacts
of nonnative species
 Box 9.2 using models to improve
control of introduced rabbits in
Australia?
3
Supplements
 Case study 9.1 invaders in an invasible land:
the case of the North American beaver in
the Tierra Del Fuego- Cape Horn region of
South America
 Case study 9.2 tracking aquatic invasive
species
 Case study 9.3 When a beauty turns beast
 Case study 9.4 Biological control as a
conservation tool
4
Introduction
 A carnivous snail exterminates over 56
endemic snail species in the southeast
Pacific.
 A meter-long tree-climbing snake consumes
endemic birds, bats, lizards and skinks on
Guam.
 Aggressive ants and bees outcompete their
native counterparts across the Americas.
 Smallpox decimates native human
populations in North America.
 European rabbits in Australia.
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 We live in a world of introduced species.
 European trees live in Africa, African dung
beetles in Australia, Australian possums in
New Zealand, New Zealand snails in North
America, North American in South America,
South American trees in Asia, and Asian
crabs in Europe.
 These emblematic and economically
important species are introduced.
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Four major conservation-focused
questions
1. What are the impacts of introduced
species?
2. What factors determine whether an
invasion succeeds or fails?
3. How are species introduced?
4. How can we best control or even
prevent invasions to reduce their
conservation impacts?
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Table 9.1 introduced species
terminology
 Cryptogenic: applies to species whose
status- native or nonnative – cannot readily
be determined; commonly used for species
whose cosmopolitan distributions or unclear
taxonomy make their geographic origins
uncertain.
 Indigenous: synonymous to native
 Introduced: refers to a species that has
been released outside its native range;
synonymous with nonnvative,
nonindigenous.
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Table 9.1 introduced species
terminology
 Invasion: the establishment and
spread of an introduced species.
 Invader: an introduced species.
 Native: describes species that
evolved in a region.
 reintroduced: refers to intentionally
released individuals of a native
species that was locally endangered
or extinct.
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What are the conservation
implications of introduced species?
 The scale of biological invasions is
staggering (驚人巨大的).
 On the plains and prairies of North America 11%
or plants are nonnative
 In Hawaii 35% are likewise nonnative.
 Approximately 8000 shrub and herb species and
750 tree species have been introduced to South
Africa.
 Over 3000 plant species have been introduced
to the state of California alone.
10
 Worldwide, 20% of endangered
vertebrate species are threatened by
introduced species – 13% of those on
mainlands and 31% on islands.
 Among freshwater fishes, 67% of
tropical and over 50% of temperate
introductions established successfully.
 A review of 31 fish introductions found
that 77% caused native fish populations
to decline.
11
Fig. 9.1 Accumulation of established estuarine and
marine invaders in San Francisco Bay, California,
over 140 years.
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 The rate of human-caused introductions
exceeds background levels at an
unprecedented scale (空前的規模).
 Species invasions affect economics, public
health, and biodiversity.
 The estimated economic benefit of these
marketable nonnative species runs to
hundreds of billions of dollars per year in
the US.
13
 In the US, cost associated with the impacts
and control of the Eurasian zebra mussel
are estimated at $1 billion over the first 10
years of its invasion, European gypsy moth
at $11million per year, European ship
worms at $200 million per year, and purple
loosestrife at $45 million per year – and
these are only a few of the hundreds of
unwanted species introduced world-wide.
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 Many public health threats are caused by
introduced diseases.
 Smallpox, avian and human malaria, and
the red tides caused by toxic phytoplankton
can outbreak in new areas.
 The global epidemic of HIV/AIDS has
spread around the world from its native
Africa, claiming approximately 18 million
victims to date, with 5 million new
infections annually.
15
What are the impacts of introduced
species?
 Invasion impacts can be evaluated
across ecological and evolutionary
realms.
1. Both direct and indirect effects of a
single invader.
2. The consequences of multiple
invasions.
3. The impacts across a range of
ecological and evolutionary scales.
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Population and community impacts
 Introduced predators
 The brown tree snake, Boiga irregularis, is
a stunning example (頂好的範例) of the
population and community level impacts of
an introduced vertebrate predator on a
naïve island population.
 The snake’s native range extends from Australia
through New Guinea to the Solomon islands.
 Shortly after World War II, it arrived on the
island of Guam where the only native snake was
a tiny, wormlike insectivore.
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The invader, the brown tree snake,
Boiga irregularis
 The invader gradually spread across the
island but remained at low densities for two
decades until the early 1960s, when it
began to appear in large numbers.
 More and more well-fed snakes were found
in chicken coops; others were carbonized
on power lines, causing electrical blackouts
(Fig. 9.2).
 During this time, native birds began
disappearing.
 Ten species of forest birds followed a
similar pattern of decline.
18
19
關島鳥類衰減的原因？
 Pesticides, Avian diseases, introduction of
competing birds, introduced predatory rats,
cats, and other mammals.
 Today, the cumulative evidence indicates
that the nocturnal brown tree snake, which
can reach abundances up to 5,000/km2,
has been largely responsible for eating the
birds– now totaling 15 species– to
extinction (Table 9.2)
20
Table 9.2 changes in vertebrate trophic
interactions on Guam before 1945 and after the
Brown tree snake invasion (1995)
Carnivores (1945)
 Fairy tern
 Mangrove monitor
 Micronesian
kingfisher
 Oceanic gecko
Carnivores (1995)
 Brown tree snake
 Mangrove monitor
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Table 9.2 changes in vertebrate trophic
interactions on Guam before 1945 and after the
Brown tree snake invasion (1995)
Insectivores (1945)
 Pelagic (遠洋的)gecko
 Blue-tailed skink
 Mariana skink
 Spotted-belly gecko
 Mourning gecko
 House gecko
 Multilating gecko
 Moth skink
 Refous fantail
Insectivores (1995)
 Blue-tailed skink
 Mourning gecko
 House gecko
 Multilating gecko
 Moth skink
22
Table 9.2 changes in vertebrate trophic
interactions on Guam before 1945 and after the
Brown tree snake invasion (1995)
Omnivores (1945)
 Black rat
 Polynesian rat
 House mouse
 Guam Rail
 Mariana Crow
 Bridled white-eye
 Micronesian
honeyeater
Omnivores (1995)
 Black rat
 Polynesian rat
 House mouse
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Table 9.2 changes in vertebrate trophic
interactions on Guam before 1945 and after the
Brown tree snake invasion (1995)
Herbivores (1945)
 Micronesian
starling
 Philippine turtledove
 Mariana fruit bat
 White-throated
ground-dove
 Mariana fruit-dove
Herbivores (1995)
 Philippine turtledove
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Introduced competitors
 The impacts of competition are often trickier to
observe and measure than those of predation.
 The most famous of the troublesome invaders
is the Eurasian zebra mussel, which was first
found in the Great Lakes in 1998 and has since
spread into the St. Lawrence, Hudson, and
Mississippi river drainages.
 In Lake Erie, Lake St. Clair, Lake Oneida, and
the Detroit river, zebra mussels are estimated
to have contributed to 64% -100% of local
unionid extinctions, whereas habitat loss is
estimated to have contributed to 2%-30%.
25
Fig. 9.4 Percent of native unionid mussels recently dead as a
function of the relative wet weight of introduced European
zebra mussels attached to their shells.
26
Morphological and behavioral impacts
 At smaller ecological scales, invaders can
cause changes in the morphology and
behavior of native species.
 範例：
1. Predatory European green crab (Carcinus
maenas) invaded the Northwest Atlantic
coastline in the early to mid-1900s.
2. The Asian flowering plant Impatiens
glandulifera was introduced to Europe from
the Himalayas just over 100 years ago.
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European green crab
 Populations of a small native herbivoreous
intertidal snail (Littorina obtusata)
developed a significantly thicker shell that
provides some protection from predation.
 The snails responded to the crab’s chemical
cues by growing thicker shells, and had a
corresponding decrease in body mass. 而影
響其(snails)生殖力。
28
Asian flowering plant Impatiens
glandulifera
 The nectar of I. glandulifera has a sugar
content comparable to that of other
bumblebee-pollinated plants, but its nectar
production rate (0.47mg/hour per flower) is
an order of magnitude greater than that of
common native species (0.01-0.04
mg/hour)
 Pollinating bumblebees visit the invader
approximately four times more frequently
than they visit the native plants.
 Where the invader is established, visit to
the native are reduced by 50% and its seed
set by 25% (Fig. 9.7)
29
30
Genetic and evolutionary impacts
 At the genetic level, hybridization and introgression by
introduced species can fundamentally alter native
species fitness and generate new – and sometime
aggressive– hybrids and strains.
 This process occurs in both animals and plants.
 In the North Pacific, a Mediterranean mussel appears
to compete with its native congener directly and
through hybridization.
 The introduced Mallard Duck threatens the persistence
of the New Zealand Grey Duck, the endangered
endemic Hawaiian Duck and the endemic Florida
Mottled Duck by hybridizing with all three.
 In England, the introduced Atlantic cordgrass
bybridized with the native European.
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Ecosystem impacts
 Certain invaders have a disproportionate
effect on ecosystem characteristics
including habitat structure, disturbance
regimes, and nutrient cycling.
 Codgrass salt marshes (composed primarily of
Spartima spp.) are a major biological community
type on the east coast of North America, where
they are threatened by habitat loss.
 On the west coast, however, introduced
populations of these species are flourishing as
they spread across hundreds of square
kilometers of tidal mud flats.
32
 On the Atlantic coast, a major cause of
habitat loss is grazing by nutria (coypu,
Myocaster coypus, a large rodent), which
was introduced from South America to
develop fur farms in the 1930s.
 Released and escaped individuals
established a feral population that spread
quickly consuming already-threatened
marsh habitat and increasing erosion.
33
What factors determine whether a
nonnative species becomes invasive?
Fig. 9.9 the invasion process.
34
Propagule
(繁殖芽)
pressure
 所有的入侵者都需要有途徑(pathway)，讓其可以
進入其原本分佈範圍之外的地區。
 這些途徑(pathways)包含全球性的國際貿易，或
是地區性的道路興建，或是種植非本土的植物。
 Propagule pressure = the quantity, quality,
and frequency of arriving organisms.
 Propagule pressure is not a constant.
 As long as human trade and transport
continue to grow and shift around the globe,
invasion pathways will grow and shift as
well.
35
Invading species characteristics
 We think are likely to make a species
adaptable and fast-growing
 High fecundity
 Ability to spread vegetatively
 Parthenogenetic or hermaphroditic
reproduction
 Broad physiological tolerances and diet
36
Reichard and Hamilton (1997)
 Classified 114 introduced species
established in North America on the basis
of their likelihood of spread.
 Using a statistical analysis, they ranked 11
traits in their ability to correctly classify
theses species.
 Five of the traits contributed significantly to
the likelihood of spread, and six were
negatively associated. (Table 9.3)
37
Rejmannek and Richardson (1996)
 Classified 24 species of pine tree (Pinus
spp.) introduced worldwide for cultivation.
 They found only three of ten life history
characteristics contributed significantly to a
Pinus species’ likelihood of successful
invasion: short juvenile period, short
interval between seed crops, and small
seed mass.
38
Invaded community characteristics
1. The climate and habitat must be hospitable
to potential invaders.
2. The species richness, interaction strengths,
and trophic structure of the community,
must be able to accommodate new species.
 Elton (1958) proposed the biotic
resistance hypothesis that species-rich
systems were more stable and therefore
less susceptible to species outbreaks and
invasions.
39
Disturbance (干擾)
Disturbance – either natural or anthropogenic – may
make a community more easily invadable, particularly
for plants.
The biotic resistance and disturbance hypotheses are
complementary if we view them from the perspective
of resource availability.
A species-rich community with intense competition may
be less invadable until disturbance alters the
availability of resources, either by providing new
resources, or by reducing the effectiveness of
competitors, allowing an invader to establish (Fig.
9.14)
40
Fig. 9.14 A representation of the conceptual theory that
increased resource availability increases a plant community’s
41
susceptibility to invasion.
How do we mange species invasions?
 Controlling introduced species is not a
simple prospect.
 The removal of an unwanted species
may require physical control,
chemical control, biological control.
 Some invaders are readily controlled by
a single method, but more often several
approaches are needed.
42
Species-based control
 For a conspicuous species, physical control
alone may be effective.
 Physical control involves trapping, digging up,
and otherwise removing invaders.
 For a more widespread invasion, chemical
control may be more effective.
 An obvious drawback of chemical control is the
nontarget mortality.
 Biological control is most highly developed
in agricultural systems.
 In many cases, multiple approaches are
required to target a particular invader.
43
Invasion prevention
 The precautionary principle, as a policy of
guilty until proven innocent, or in terms of
good lists and bad lists of low- and highrisk species.
 Preventing invasions requires identifying
and regulating invasion pathways.
 Regardless of scale, effective invasion
prevention requires a certain amount of
legislation and policy development.
44
Table 9.5 timeline of US legislation
relating to introduced species
 1900 Lacey act, prohibits import of species that harm
wildlife.
 1912 Plant quarantine(檢疫) act, allows regulation and
quarantine of nursery stock for plant diseases and
insect pests.
 1931 Animal damage control act, allows control of any
animal that damages agriculture, aquaculture, public
health, or other enterprise.
 1939 Federal seed act, regulates import and transport
of seeds, especially of noxious weeds.
 1944 USDA organic act, allows federal eradication(消
滅) of plant pests, including noxious weeds.
 1957 Federal plant pest act, prohibits import and
transport of plant pests.
45
 1974 Federal Noxious weeds act, regulates
the transport of plants listed as noxious.
 1977 President Carter’s Executive order
11987, Restricts federal agency
introduction of nonnative species into “any
natural ecosystem”.
 1990 National aquatic nuisance prevention
and control act, establishes voluntary (自願
性的) ballast water management guidelines.
 1996 National invasive species act,
establishes compulsory(強迫性的) ballast
water management guidelines.
46
 1999 President Clinton’s executive order 13112,
establishes National invasive species council, with a
mandate to develop a National invasive species
management plan coordinating all federal on activity
introduced species.
 2000 Plant protection act, regulates plant pest
transport, both accidental and intentional for biological
control.
 2001 National invasive species management plan,
Mandated by Executive Order 13112, provides a
blueprint for federal prevention management,
research, and outreach on introduced species.
47
Case study
 9.1: invaders in an invasible land. The case
of the North America Beaver(河狸) (Castor
canadensis) in the Tierral del Fuego-Cape
Horn region of South America.
 9.2: Tracking aquatic invasive species
 9.3: When a beauty turns beast. Caulerpa
taxifolia: one of the world’s worst invasive
species.
 9.4 Biological control as a conservation tool.
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問題與討論
http://mail.nutn.edu.tw/~hycheng/
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