Transcript Chapter7

• Biological invasions
represent one of the leading
threats to natural ecosystems
and biodiversity, second only
to habitat transformation.
• Alien species affect native
species and ecosystems in
numerous ways, with effects
that are usually irreversible.
http://www.angelfire.com/nt/57pipesanddrums/57.html
ECOLOGICAL IMPACTS
• Parker et al (1999) devised the following equation to measure
impact:
I (impact) = R (range) x A (abundance) x E (effect)
• Range and/or abundance are often used individually to infer
impact but there are flaws with this: it is assumed that impact
increases with range size, but impacts on an island can be
greater than those on the mainland. Impact is also assumed to
increase with abundance but this relationship is not always
linear or true for all species.
This equation, though simplified, gives the best representation of
quantification of impact that can be compared between species.
http://www.popartuk.com/photograph
y/maldive-morning-2834-poster.asp
• The impact of invasive species is difficult to measure.
ECOLOGICAL IMPACTS cont.
• NB impact, rather than establishment that threatens indigenous
species. The impact of an invader can be measured at 5 levels:
1. Effects on individuals:
changes in demographic rates, viz. mortality,
and reduced growth or reproduction
morphology of individual organisms may also change
behavioural impacts occur when individuals change habitat use
or activity patterns in response to new predators or competitors
ECOLOGICAL IMPACTS cont.
2. Genetic effects – either direct, as a result of altered
patterns of natural selection or gene flow within
indigenous populations, or indirect, through hybridization
and introgression.
3. Population dynamic effects – impact on the abundance and
dynamics of particular indigenous species, the most
extreme being complete extinction.
e.g. when gypsy moth outbreaks occur in
North America, the white-footed mouse
populations that feed on them also peak,
increasing tick populations - consequently
the incidence of lyme disease also peaks
http://www.wmnh.com/wmiab07.htm
ECOLOGICAL IMPACTS cont.
• Alien species have contributed to the decline of 42% of US
endangered and threatened species (Schmitz and Simberloff,
1997). They are the main cause of recent bird extinctions.
Over the last 500 years, alien spp. have been partly or wholly
responsible for the extinction of at least 65 bird species.
Island species are particularly susceptible (Birdlife
International, 2004).
ECOLOGICAL IMPACTS cont.
4. Community effects – high profile invaders are assumed to
cause overall reductions in biodiversity. However, many
invasions may actually increase total species richness
5. Effects on ecosystem processes – changes in species
composition (additions of a new species, substitution of the
invader for one or more indigenous species, or loss of
indigenous species diversity) and disturbance regimes
(Parker et al, 1999).
ECOLOGICAL IMPACTS cont.
• Transformer species: Aliens can use resources excessively
eg. water, light and oxygen so that they are no longer
available for the indigenous plants. They can also add
resources eg. nitrogen to the soil.
• Aliens can promote or suppress fire, thereby
changing the disturbance regime leading to
sometimes dramatic effects on the indigenous
plants.
• Aliens can be discrete-trait invaders (DTIs) or continuous-trait
invaders (CTIs). DTIs add one or more new functions to an
ecosystem (e.g. improvig nutrient levels in nutrient-poor soils),
CTIs differ slightly from indigenous species in providing one or
more functions that already exist (i.e. no new functions)
Chapin et al (1996).
ECOLOGICAL IMPACTS cont.
• Disturbance regimes: Aliens either introduce, enhance or
suppress events such as fire and erosion, or are themselves
agents of disturbance – disrupting soil or sediment, or killing a
significant amount of the community in a relatively short period
of time (Mack and D’Antonio, 1998).
• The spread of fire-adapted plants that burn easily increase the
frequency and severity of fires, to the detriment of property,
human safety, and indigenous fauna and flora (Schmitz and
Simberloff, 1997). Fire is usually more intense when burning in
alien vegetation. Remember the 2000 fires in Cape Town?
Alteration
Example
Fire enhancement
Grasses increase rates of fire frequency,
spread, and/or spatial extent
Fire suppression
Trees decrease fine fuel load and fire
spread in grassland or open woodland
Increased erosion
Trees increase stream bank collapse in
riparian zones
Decreased erosion
Plants stabilize mobile substrates
Increased biotic disturbance
Pigs increase soil disturbance
Increased biotic disturbance
Pests or pathogens cause stand-level or
population-level dieback
Change in consequences of
disturbance
Invader changes susceptibility of
community to physical forces of
disturbance
Table 1. How invaders alter disturbance regimes (Mack and
D’Antonio, 1998)
ECOLOGICAL IMPACTS cont.
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For example, here follow some effects of alien species in aquatic
environments:
changes in resource competition (food, space, spawning areas)
physical changes in habitat (reduced water movement, erosion,
alteration of substrate)
limitation of resources (nutrients, light, oxygen)
detrimental changes in trophic web due to introduction of new
functional group
harmful algal blooms
genetic effects on indigenous species (hybridisation, change in
gene pool, loss of indigenous genotypes)
drastic reduction of population size or even extinction of
indigenous species (BioMare, 2004).
ECOLOGICAL IMPACTS cont.
Feedback loops: Grass invasions can initiate and maintain a
grass-fire feedback system that prevents the regeneration of
indigenous woody species over large areas. The cycle can begin
after purposeful land clearing or after the invasion of
woodlands/shrublands by alien grasses.
introduction of alien grasses
woody vegetation
and/or
land clearing
fire
microclimate change
selection for grass
grassland/savanna
SOCIAL IMPACTS
• Globalisation brings many new medical threats. Global
environmental and climate change is expected to lead to range
expansion of many viruses potentially dangerous to humans.
• Chapter 6 covered much about parasites and pathogens that can
affect human (and animal) health and well-being.
• E.g. In India, introduced black rats bite ± 20 000 people per year,
resulting in hospital admittance (Pimentel et al, 2001).
• Human health can also be impacted by
species that pollute (decompose or
release chemicals into) water resources.
Reduced volumes and quality of water
and food crops due to many alien pests
can cause famine and starvation.
SOCIAL IMPACTS cont.
http://www.bouman102.nl/Pinus%20radiata.jpg
• Many indigenous spp. are used in cultural practices and for
medicinal purposes. Losses of these species due to invasive
aliens would be a social or cultural impact.
• Benefits and costs of introductions are unevenly distributed
among ecosystems, within and across regions, among sectors of
society, and across generations. Although an introduction may
meet a desired objective in an area, at a certain time and for some
sectors of society, unwanted and unplanned effects may also
occur (Ewel et al, 1999).
• The relative magnitude of costs and benefits vary in space and
time. eg. In SA, some Pinus spp. are commercially important, but
cause expensive problems when they spread from plantations into
watersheds and conservation areas (Richardson and Higgins,
1998)
ECONOMIC IMPACTS
• Measuring the economic impact of alien species often assists
managers and funding organisations to determine priorities for
control – the species causing the most economic damage or loss
are often the first to be controlled, or at least assessed for
control.
However, many of the impacts relate to
change in ecosystem structure, or
extinction of individual species, which are
very difficult to attach monetary values to.
http://www.abesy.de/web/consult1.html
• Alien species invasions cause more that US$ 314 billion per
year in damage around the world. Many invasive alien
species have caused major economic losses in agriculture
and forestry (Pimentel et al 2001).
ECONOMIC IMPACTS (Pimentel et al, 2001).
Weeds in US agriculture cause 12%
Pest insects and mites cause about
reduction in potential crop yields.
US$ 16 billion in crop losses in the USA
It is likely that non-native weeds
each year.
result in US$ 27.9 billion in losses.
Crop losses caused by introduced insect
The house
sparrow
In South Africa, alien
cause
crop
andweeds
mite pests
intotal
South
Africa are ±
and
the
european
losses of about US$
billion per
per year.
year
US$1.5
1 billion
starling together
cause ± US$ 1 billion
yearininthe
crop
Crop per
losses
USA due to alien plant
damages
in
the
USA.23.5 billion per year.
pathogens come to ±US$
± 85% of plant pathogens attacking crops in
SA are thought to be introduced: US$ 1.8
billion per year in crop losses.
http://www.kolkatabirds.com/page16.htm
• European purple loosestrife in the US, has changed the
structure of most the wetlands it has invaded. ± US$ 45 million
is spent on control of purple loosestrife each year (Pimentel et
al, 2001).
• Water hyacinth is a major weed in South Africa, where it is
reducing already scarce water resources (Richardson et al,
1997). More than US$ 25 million is spent per year on control of
water hyacinth.
http://cropwatch.unl.edu/photos
/weedpho.htm
http://www.waterscapes.
ca/safety.html
• More than US$ 5 million per year is spent on preventing future
alien plant invasions in South Africa (van Wilgen et al, 1998).
ECONOMIC IMPACTS cont.
• Domestic mammal introductions include dogs, cats, cattle,
horses, sheep, pigs and others. Other introduced species are the
house mouse, European rabbit, brown rat and the black rat.
• In the US, it is estimated that an individual adult rat causes US$
15 in damage per year; so with approximately 1.25 billion rats, the
cost is astounding. Rats are also major vectors for and carriers of
human and livestock disease (Pimentel et al, 2001).
http://coastal.er.usgs.gov/navassa/hike/lh15.html
http://wonderclub.com/Wildlife/mammals/brown_rat.html
ECONOMIC IMPACTS cont.
••Pigeons
In Australia,
cats decimate
bird, mammal,
causeferal
problems
in the UKindigenous
fouling buildings,
statues, cars,
and
amphibian populations.
There
are ± grains,
3 million
pet
andmarsupial
sometimes
pedestrians.
On farms they
consume
causing
cats and and
18 million
ferallosses.
cats in They
Australia
(Anon,
1996).
production
economic
are also
responsible
for
transmitting
at least
poultry
andPrince
Bracewell,
1986).
• Pet and feral
cats 3are
also adiseases
problem(Bevan
in SA. On
Edward
Damages
thecats
UK are
US$
270 million
per year.significant
Island, in
feral
prey± on
native
birds, causing
problems with the burrowing petrels (Procellaria sp.) (Huntley,
1996).
http://college.laboetie.free.fr/parcours/pigeon2.htm
http://college.laboetie.free.fr/parcours/punk.htm
ECONOMIC IMPACTS cont.
The brown tree snake (BTS) was accidentally introduced to Guam
immediately after World War II when military equipment was moved
onto Guam (Fritts and Rodda, 1995). Soon the snake population
reached densities of 100 per hectare, dramatically reducing
indigenous bird, mammal and lizard populations, causing major
problems for small farmers and pet owners. The BTS is thought to
have resulted in the extinction of 9 endemic bird species, 5
indigenous lizard species and 2 bat species (Armand, 2000). The
snake crawls up utility poles and has caused a total of 1500 power
outages on the island, amounting to a cost of US$ 1 million per
year. The snake is slightly venomous & causes health problems
amounting to US$ 25 000 per year (Pimentel et al, 2001).
ECONOMIC IMPACTS cont.
• IAS amount to higher agricultural costs, because of losses,
damages and control costs. There are also losses to the
livestock industry because of poor forage material – most
invasive plant species don’t make for suitable forage, as they
are unpalatable and often toxic.
• Aquatic IAS can compete with and reduce commercial fish
stocks. Toxic blooms can affect aquaculture. Clogging of water
intake pipes and fouling of boats and buoys result in cleaning
costs and antifouling painting (BioMare, 2004).
• The zebra mussel, Lantana, kudzu, Brazilian pepper and rats are
all economic and ecological catastrophes.
INVASION MELTDOWN
•• Are
invasive
species
facilitating
the success
of successive
Multiple
invasions
can
have a synergistic
impact,
meaning the
invasions?
problems created are bigger and more dramatic. E.g. the sea
lamprey paved the way for two other invaders. By the 1950s, the
• Invasional
meltdown
defined
as the
process byof
which
a group
sea lamprey
invasionis
killed
off most
populations
indigenous
of
non-indigenous
species
facilitate
another’s
in
trout
in the Great Lakes.
The
removalone
of this
naturalsurvival
predator
various
ways,
the likelihood
survival
and/or
paved the
wayincreasing
for the explosion
of smeltofand
alewife
fish of
ecological
impact,
possibly
the zooplankton
magnitude ofand
theindigenous
impact
populations,
whichand
in turn
reduced
(Simberloff
and
Von Holle,
1999).in overall fish productivity in the
planktivores,
causing
a decline
system.
http://www.unb.ca/fredericton/science/biology/Fish_key/
Clupeidae/Alewife.htm
http://www.nps.gov/isro/NR_Profile_Internal/NR_stills/fish_imag/pages/rainbow%20s
melt_jpg.htm
INVASION MELTDOWN
Another example: African crystalline ice plant invades existing
plant communities in California through preferential grazing by
animals on native plants. Once it is established, it accumulates
salt, which is released when the plant dies, through leaching by
fog and rain. The salt then produces an osmotic environment
intolerable to the indigenous plants (Vivrette and Muller, 1977).
When wind or other disturbance creates openings in the ice-plant
carpet, these are colonised by the ice-plant itself, or by other
alien plants.
http://www.uib.es/depart/dba/botanica/herbari/generes/Mesembryanthemum/crystallinum/Mesembryanthemum_crystalinum(f
l)_f_s.jpg
General model of invasion of alien plants facilitated by
mutualisms – “invasional meltdown” (Richardson et al, 2000).
Chapter 1 Definitions
Chapter 2 History, globalisation and GMOs
Chapter 3 The human dimension
Chapter 4 Pathways of introduction
Chapter 5 Characteristics of invasive alien species
Chapter 6 The ecology of biological invasions
Chapter 7 Impacts of invasive alien species
Next
Chapter 8 Invasive species management
Chapter 9
Chapter 10
Chapter 11
Chapter 12
I hope that you found chapter 7 informative and that
you will enjoy chapter eight!