Download 3.3 Community Interactions

(Sec 3.3 pg 68-73)
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Each species has a special role that it plays within the
ecosystem.
A niche is the overall role of an organism in the
community, including the range of abiotic and biotic
factors the organism requires and can tolerate.
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No two species can occupy the same niche (Fig.1
p.68), but many species compete over the same
limited common resources.
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There are two main types of competition:
Inter-specific competition = when two different species
compete for the same resources.
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There are two main types of competition:
Intra-specific competition = when organisms of the same
species compete for the same resources.
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Some adaptations that allow species to reduce
competition include:
Resource partitioning = when two competing organisms use
the same resource but at different times, in a different way, or
in a different place.
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Some adaptations that allow species to reduce
competition include:
Adaptive radiation = when a single species develops a way to
become specialized at exploiting smaller parts of the niche (one
species becomes many).
For example, one species of bird that eats nuts and fruit could
evolve into two species of bird – one a specialized nut-eater, the
other a specialized fruit-eater.
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When foreign species (also called ‘introduced’ or
‘alien’ species) move into an area they may be able to
out-compete native species for a particular niche, fill
a niche that was not previously filled, or put pressure
on native species to adapt in new ways or go extinct.
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Humans have introduced many foreign species to
new environments (often unintentionally), and some
have had devastating effects (e.g. scotch broom). See
Fig.3,4,5,6,7 p.69&70.
Introduced foreign species can dramatically reduce
local biodiversity.
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Newly cleared land is always colonized by new plant
communities.
The gradual change in the types of plants that
represent the structure of a community is called
ecological succession.
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After land is cleared, pioneer species are first to
colonize a new environment.
The pioneer species change the environment in a
way that allows other plants to colonize, and these
other plants eventually out-compete the pioneer
species
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Ecological succession generally takes place in two
ways:
Primary succession = occurs in lifeless, barren areas (e.g. rock).
First producers to move into the area are mosses, lichens, etc.
They help to break down the rock and trap tiny pieces of windblown soil to form new soil.
Grasses and small shrubs begin to grow. Left undisturbed, the
community will eventually develop in to a stable ecosystem
known as a climax community.
Please note primary succession can also occur in aquatic
environments (Fig.9 pg.71).
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Ecological succession generally takes place in two
ways:
Secondary succession = begins in areas that already have soil.
There may have been a disturbance (fire, flood, forest
harvesting).
The community will go through different stages of dominant
plant types (grasses/shrubs → fast-growing sun-loving trees →
slower-growing shade-tolerant trees) until it reaches the climax
community.
Succession Video:
http://www.youtube.com/watch?v=k03vxRYsJ4Y