Week 7
• Tuesday: Complete G1 Guided notes
worksheets
• Wednesday – Data Collection outdoors!
• Friday – COMPUTER LAB IN MONTICELLO –
EXCEL AND DATA ANALYSIS
COMPLETING G1
•
•
•
•
COMPETITION
NICHE CONCEPT
COMPETITIVE EXCLUSION
NICHE PARTITIONING
What is ‘competition’ in Ecology?
Competition occurs when individuals use a shared
resource in short supply: There may not be enough of
the resource for any given individual to survive, or to
reproduce, as well as when more resource is present.
Competition does not necessarily involve competitors
ever meeting (if the competitors are mobile
organisms, such as many animals), or being adjacent
to each other (if sessile organisms, such as plants or
fungi).
As a result of competition:
• Birth rates are lower, death rates higher, or
both.
• In ecological terms, population growth rates
decrease and population size is lower at
equilibrium
• In evolutionary terms, an individual's fitness is
lower.
• Competition is a density dependent effect on
population dynamics
Competition can be intraspecific or
interspecific
Interspecific
Competition
Competition
between different
species which
depend on the
same resource:
• Food
• Water
• Nesting Sites
• Breeding Sites
Intra-specific competition
• Example: Adaptive
Radiation in Darwin’s
Finches
• Example: Competition for
mates
LET’S REVIEW OUR INTER-SPECIFIC
RELATIONSHIPS
• PBS marine interactions
• Marine Mutualism
The Niche Concept: Definition
• ‘Nicher’ – to Nest:
• A term describing
the way of life of a
species:
The specialised
habitat of an
organism:
• space and territory
• Nutrition and feeding
habits
• Interactions with other
organisms
• Its reproductive habits
• Its role in the community
The Niche concept: A Working
Analogy
In 1927, Charles
Sutherland Elton, the
British Ecologist, stated:
‘When an ecologist states
‘There goes a badger’, he
should include in his
thoughts a definite idea of
the animal’s role in the
community, just as if he
had said ‘There goes the
vicar’
Niche Concept: The Boundary
conditions
Two species that use
exactly the same
resources cannot
occupy the same niche
Only one species or
population can occupy
the same niche for an
extended period
Fundamental and Realised Niches
Fundamental Niche
A species’ fundamental
niche is the full range of
environmental and social
conditions under which it
could potentially survive and
reproduce
Realised Niche
The realised niche is the
specific set of conditions in
which it survives in a given
habitat or ecosystem, given
the other species or
limitations present.
These are the conditions to
which the species is best
adapted.
The Competitive Exclusion Principle
Aka ‘Gause’s Law’
‘No two species can occupy the same
niche for a prolonged time’
The Competitive Exclusion Principle
• If two species share a
niche, there must be interspecific competition for
resources
• The best adapted species
will survive
• The loser will struggle to
survive and reproduce, and
will eventually become
extinct OR migrate (if its
niche is broad enough)
Examples are abundant
• Invasive species
• Red versus Grey
Squirrel in Western
Europe
• Gause’s Paramecium
Competitive
Exclusion:
Squirrels
Competitive Exclusion: Squirrel
Distribution
The Classic Example of Competitive
Exclusion: Paramecium
Georgy Gause cultured 2
species of the protist
Paramecium:
• P. Aurelia
• P. Caudatum
• Grown together under
ideal conditions, both
populations reach a higher
maximum
• Grown together, one
species rapidly becomes
extinct…
Does Competitive Exclusion work in
the real world?....
The competitive Exclusion principle is actually
rarely observed in natural ecosystems:
• ‘spatial heterogenity’ (niche partitioning)
• Niche sharing associated with availability of
multiple resources
• ‘The paradox of the plankton’: Why do so
many plankton species exist in a small,
limited, homogenous habitat?
Niche Partitioning
1. Spatial: Two different species use the same resource
by occupying different areas within the range of the
resource
2. Temporal: Two species eliminate direct competition
by using the same resource at different times
3. Morphological: Two different species evolve different
morphologies in order to use a resource in different ways