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BGYC63 Oct04

Biological Sciences
Course Code
Ivana Stehlik

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BIOC63 Oct04
Threats to BIodiversity
invasive species and thier effects on local communities
Invasive Species
A. Definition and scale of invasion
Native species: a particular species that historically occurred or currently occurs in an ecosystem
Introduced species: a species that is new to a habitat (that has immigrated) that didnt occur before
(it is just new, dont say the effect)
Invasive species: a species that is also new to the area, but has a negative effect to the native
Biological Incation; the movement of species from one area to another new area
- since humans started to move around, the amount of species invasion has risen
- the more people travel, the more species get moved around
- especially after the industrial revolition
- when you look at the makeup, 22% of species in canada is alien, and in ontario, 32% is
- when you compare this to islands, it is even Ascension, it is 82%
- generally in island settings, the percentage is much higher because once they get
there, they cant leave
- looking at the local scale (Ontario), we can see that within the invasive species, plants
have the highest percentage
- on a global and also on a local scale, the number of invasive plants is always much higher
than any other living organisms
- when we look at proportion of invasive plants, ontario is #1
B. Typical course of Invasion
- pathways of plant introduction in Canada
- of the 141 species of plants introduced intentionally were introduced as ornamental or
landscaping plants (gardening) , then as agricultural crop
- of the 120 species of plants introduced unintentionally, more than 75% were introduced
with plant products (contaminants in seed, wood products)
- the non-native species that turn into invasive species follow similar patterns
- first they are in very low numbers for a long time "lag phase", which can take from 10-200
years...and most of non-native species stay in this lag phase and never take off....but some
take into the "log phase" where they increase in number until they inhabit all area that they
C. Reasons for success of Incadoers: Enemy Release Hypothesis
Why are invasive species so successful?
Enemy Release Hypothesis (ER)
- they escape from their enemies so the native species (still with thier competitors)
are frequently out-competed
- in a native area, all are fed relatively equally, but in a non-native area, the invasive
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