slides on biological invasion

1. THEORIES AND HYPOTHESIS OF
BIOLOGICAL INVASION
By Kanchan Parajuli
MSC Assignment 2013
kanchanparajulimsc@gmail.com
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2. In general Biological invasion can be defined as the
process by which species( or genetically distinct
population either plants or animals), with no
historical record in an area, breach biogeographic
barriers and extend their range.
According to Williamson (1996) a biological invasion
happens when an organism arrives somewhere
beyond its previous range of distribution, and
impacts upon indigenous species.
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3. Therefore, a biological invasion "produces a significant
change in terms of community composition" (Cronk &
Fuller 1996).
 INVASIVE ALIEN SPECIES (IAS).
According to Global Invasive Species Programme: “IAS
are organism that have been moved from their native
habitat to a new location where they cause significant
harm to the environment, economic systems and human
health”.
Any species including its seeds, eggs, spores or other living
entities through which it is capable of multiplying and
propagating in a foreign ecosystem could be an alien species.
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4. Common traits:-
Fast growth
Rapid reproduction
High dispersal ability
Phenotypic plasticity( the ability to alter growth
form to suit current condition).
Tolerance with wide range of environmental
condition
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5. IMPACTS
The impacts of IAS are immense, insidious, and may be irreversible and
they may be as damaging to native species and ecosystem on a global
scale as the loss and degradation of habitat. IUCN/SSG/ISSG 2000
According to Birdlife International 2004,GISP 2004, Howard 2003,
IUCN/SSC/ISSG 2004, UNEP 2004,
Over the last 500 years, IAS have been responsible for extinction of
at list 65 bird species.
IAS, especially predators, directly threaten more than 300 bird
species.
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6. kanchanparajulimsc@gmail.com 6
• One of the most notorious IAS is water hyacinth which grow
quickly and harms the wetland ecosystems by blocking sunlight
and oxygen, altering water-flows and increasing
evapotranspiration. It costs some countries tens of millions of
dollors to control.
• Similarly, African nations alone spend an estimated US$ 60 million
annually to control water weeds like water hyacinth (Gould, 2004).
• The water fern enhances the breeding of mosquitoes and snails
that carry bilharzia, which infects about 300 million people
annually in the tropics.

7. Indian Hoese Crow, feasting on a small mammal on Kenya.
The Indian House Crow destroys the habitat of many other birds in
Tanzania. The House Crow came with sheep from India, probably late
1800s. This bird kills other species, destroys nest, and steal eggs and
chicks of the domestic chicken. It also spreads disease and is generally
a serious pest in towns along the coast of Eastern Africa (Howard
2003). kanchanparajulimsc@gmail.com 7

8. Brown Tree Snake
Brown tree snake , introduced to Guam Island from New
Guinea in Cargo after world war II, has cause the
extinction of 9 of the 12 native forest birds in Guam and 2
of the 11 native lizard species (Lockwood et al. 2007).
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9. Theories and Hypothesis
1. Tens rule:- Williamsons and Fitter (1996). Proposes that in UK 1 in 10
of this species imported appears in the wild (introduced or causal),
1/10 become established and 1/10 become truly invasive. Looking
deeper into the subject there are four stages for a species to become
invasive.
 Transport
 Establishment
 Spread
 Impact
2. Biotic Resistance Hypothesis:- Ecosystems with high biodiversity are
more resistant against invaders than ecosystems with low biodiversity
(Elton 1958; Levine andD’Antonio 1999; Lonsdale 1999; Mack et al.
2000; Maron and Vilà 2001; Shea and Chesson 2002; Levine et al. 2004;
Fridley et al. 2007; Jeschke and Genovesi 2011).Interspecific relation
existing in the environment( eg. Predation, competition, parasites)
make invaders eatablishment more difficult. This hypothesis was
mainly supported by experimental studies with mesocosm (artifically
constructed community) (Tilman 2000).
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10. 3. Biotic Acceptance Hypothesis:- Natural ecosystem
tend to accept more invasive species independent of the
native species, summing up: Rich get richer.
Stohlgren and colleagues (2006) studying plant richness
in different state in USA showed that the richest states in
plant species also had more invasive plant species.
4. Island Susceptibility Hypothesis:- Invasive species are
more likely to become established and have major
ecological impacts on island than on continents (Elton
1958; Simberloff 1995; Shea and Chesson 2002; Jeschke
2008). This is related to Biotic resistance Hypothesis, as
continent typically have higher biodiversity than islands,
mainly due to geographic and thus evolutionary
isolation.
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11. 4. Novel weapon hypothesis:- In the exotic habitat, invasive species
can have a competitive advantage against native species because they
possess a novel weapon, i.e. a trait that is new to the resident
community of native species and therefore affects them negatively
(Callaway and Aschehoug 2000; Callaway and Ridenour 2004). Prime
examples of novel weapons are plant biochemical's with allelopathic
effects, but traits of other organisms can be considered as novel
weapons as well, e.g. toxic substances produced by invasive cane toads
(Bufo marinus).
5. Enemy release hypothesis:- The absence of enemies in the exotic
range is a cause of invasion success (Maron and Vilà 2001; Keane and
Crawley 2002; Mitchell and Power 2003; Torchin et al. 2003; Colautti et
al. 2004; Liu and Stiling 2006; Blumenthal et all. 2009). Invasion
opportunities arise when natural enemies, such as disease, predators
and parasites are in low abundance or are less effective against new
species.
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12. 6. Climate matching hypothesis:- which argues that the
climatic similarity between the exotic and native range
determines the success of an invasive population.
7. Invasional meltdown Theory:- This theory says that the
establishment of one invasive species in an ecosystem
facilitates invasion to additional non native species,
increasing their likelihood of survival or ecological impact
(Simberloff and Von Holle 1999).
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13. Zebra Mussel (Dreissena polymorpha)
Example 1, when Zebra mussel (Dreissena polymorpha) invaded the great lakes during
mid 1980s, their voracious appetites for phytoplankton improve water clarity and the
penetration of sunlight into deeper waters of the lakes. The extra sunlight, in turn,
helped to facilitate the invasion of the Great Lakes by exotic Eurasian Watermilfoil
plants.
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14. Cheat Grass (Bromus tectorum)
Example 2. In Western USA when Livestock such as cattle and sheep
were introduced into the region, Grazing and trampling of native grasses
by the livestock is thought to have helped to faciliate the invasion of the
area by the exotic cheat grass (Bromus tectorum).
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15. References
Tiwari, S.,Adhikari, B.,Siwakoti, M.& Subedi, K.(2005). An Inventory and Assessment of
Invasive Alien Plant Species of Nepal.
Jeschke JM, Gómez Aparicio L, Haider S, Heger T, Lortie CJ, Pyšek P, Strayer DL (2012) Support
for major hypotheses in invasion biology is uneven and declining. NeoBiota 14: 1–20. doi:
10.3897/neobiota.14.3435
Robert I. Colautti*, Igor A. Grigorovich & Hugh J. MacIsaac Great Lakes Institute for
Environmental Research, University of Windsor, Windsor, ON, Canada N9B 3P4;
Lauren M. Pintor,1,2,* Joel S. Brown,2 and Thomas L. Vincent3 (2011). Evolutionary Game
Theory as a Framework for Studying Biological Invasions.
Shea, K.,Chesson, P. (2002). Community ecology theory as a framework for biological
invasion.
Jacob N. Barney Æ Thomas H. Whitlow. (2008) A unifying framework for biological invasions:
the state factor model
Sodhi, N.S, Ehrlich, P.R. (2010). Conservation Biology for All. Oxford University 2010.
http://en.m.wikipidia.org/wiki/island_biogeography
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16. Zebra Mussel (Dreissena polymorpha)
Thank you very much for
your kind attension.
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