Community Ecology

Friday, October 19th: Period E
• 1. An update on EXCEL 2011
• 2. Homework Review
• 2. Completing Topic G.1, Community Ecology
EXCEL – Revised, Improved
• Please complete your temperature assignment by
Tuesday. The worksheet (revised for EXCEL 2010) is
accesible on the Class Blog
• Please contact me if you don’t have access to
EXCEL, or if you need some help
• Use your IB Independent Assessment Guide – it
has all of the answers to your questions!!
• Online help:
• Getting started with EXCEL
Homework Review: Factors
Affecting Plant and Animal Species
i-Biology Link
i-biology hyperlink
Homework Review: Relationships
Between Species
Relationships Between Species
Plant: +/-
Primary Consumer +
Predator: +
Prey: -
Host: -
Parasite: +
Species 1: +
Species 2: +
Species 1: 0
Species 2: 0
Let’s Check those relationships…
It's David....(3.30)
National Geographic Anemones/clownfish
PBS marine interactions
Marine Mutualism
• Competition!
• The niche concept
• Competitive exclusion
• Niche partitioning
‘Competition’ in Ecology?
When does it happen?
• Shared resource in short supply
• Competion is a density dependent determinant of
population dynamics
Do competitors have to meet each other?
Competition can be between individuals of the same species
(intra-specific) or between different species (inter-
Intra-specific competition:
Competition for mates
• Male Bighorn Sheep
• Bisons headbutting
Intra-specific competition: Darwin’s
• Darwin's Finches
Interspecific Competition
Competition between different species which depend on the
same resource:
• Food
• Water
• Nesting Sites
• Breeding Sites
Examples: spades...
The Niche Concept
Topic G.1.5: Explain what is meant by
the niche concept, including an
organism’s spatial habitat, its feeding
activities and its interactions with
other species
The Niche Concept: Definition
‘Nicher’ (French): to Nest
• A term describing the way of life of a population
• To describe a population’s niche, you need to
describe its ‘specialised habitat’:
– space and territory
– Nutrition and feeding habits
– Interactions with other organisms
– Its reproductive habits
– Its role in the community
The Niche concept: A Working
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
Defining a Niche : ‘The Boundary
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
G.1.8: Distinguish between
fundamental and realized
Fundamental Niche
A species’ fundamental niche is the full range of
environmental and social conditions under which it
could potentially survive and reproduce
‘potential niche’
• Some species have a broad fundamental niche
• Some species have a narrow fundamental niche
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 population is best
‘Realised Niche’ is not a constant for a
• In fact, populations of the same species may
occupy different realised niches within different
• It all depends on the other species and
environmental factors involved in ‘sharing of the
Let’s look at some examples….
G.F. Hutchinson’s Definition of the
Hyperdimensional Niche…
Homework for Monday
• Research information for two species of your
• One can be the Clown-fish
• The other can come from the WWF website:
• WWF species directory
G.1.7: Explain the principle of
competitive exclusion
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
• 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
• Gause’s Paramecium
Competitive Exclusion: Squirrel
G.1.7: Outline the method and importance
of G.F. Gause’s paramecium experiments
Gause's Struggle for existence can be accessed
in full online (even in Russian!)!
G.1.7: Outline the method and importance
of G.F. Gause’s paramecium experiments
Georgy Gause cultured 2
species of the protist
• P. Aurelia
• P. Caudatum
• Grown together under
ideal conditions, both
populations reach a higher
• Grown together, one
species rapidly becomes
Let’s think about it…..
How does environmental change
affect a species with a broad
Species with a broad niche
• ‘Generalists’
• Widely distributed
• Adaptable
Red-Tailed Hawk
Let’s think about it…..
How does environmental change
affect a species with a narrow
Species with a narrow Niche
• ‘Specialists’
• Not adaptable
• Under threat of
extinction if the niche
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/ partitioning 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
As there is a limited about of space and resources on
Earth, organisms can use 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
Spatial Niche Partitioning
Closely related
bird species
occupy different
foraging locations
on a single tree
Temporal Niche Partitioning
Different species of spiny
mouse inhabiting the
same ecosystem may be
either nocturnal OR
diurnal feeders
Morphological Niche Partitioning
Different beak sizes
have allowed
adaptive radiation
of finches in the
Galapagos Islands

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