Community interactions: the niche
concept and symbiotic relationships
Any species has a well defined
Any population of that species
habitat
has a well defined niche
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‘its address’
Where it can live
What it needs to eat
Breeding grounds
Water requirements
etc etc
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‘its occupation’
The species it interacts with
The species it depends on
The species that depend on
it…
• HABITATS ARE DEFINED • NICHES CAN GROW AND
AND CONSTANT
SHRINK, DEPENDING ON
‘EXTERNAL’ FACTORS
Habitat
The area where an
organism lives is
called its habitat.
A habitat includes
both biotic and
abiotic factors
‘Nicher’ (French): to Nest
A term describing the way of life of a population
No two species can occupy the same niche in the same
ecosystem
To describe a population’s niche, you need to describe its
‘specialised habitat’:
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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’
Defining a Niche : ‘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
A population has a fundamental AND a
realised niche
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
Species with a broad niche
• ‘Generalists’
• Widely distributed
geographically
• Adaptable
Species with a narrow Niche
• ‘Specialists’
• Not adaptable
• Under threat of extinction if the niche changes
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
adapted.
‘Realised Niche’ is not a
constant for a species
• In fact, populations of the same species may
occupy different realised niches within different
ecosystems
• It all depends on the other species and
environmental factors involved in ‘sharing of
the resources’
What interactions occur within
communities?
All community interactions play an essential role
in survival of both species
Essential Interactions
Predation
Parasitism
Mutualism
(Commensalism)
Competition
Symbiosis
Any ‘long term’ relationship in which two
species live closely together is called
symbiosis.
Symbiotic relationships include:
• mutualism
• commensalism
• parasitism
• (predation)
‘Symbiotic’ relationship 1: Predation
Predation
An interaction in which one organism
captures and feeds on another organism is
called predation.
The organism that does the killing and
eating is called the predator, and the food
organism is the prey.
Parasitism: one organism (the parasite) lives on or
inside another organism (the host) and harms it.
• yuk.....!
• The parasite of the day Blog...
Community Interactions
Mutualism: both species benefit from the
relationship.
Commensalism: one member of the
association benefits and the other is
neither helped nor harmed.
Symbiotic relationships can take place between
species from different kingdoms!
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Symbiosis
Mutualism, Commensalism and parasitism
Sunfish and seagulls...
Fish Cleaners
Giving Fish a bath
Clownfish and anemones
Competition
Competition occurs when organisms of the same or
different species attempt to use an ecological
resource in the same place at the same time.
A resource is any necessity of life, such as water,
nutrients, light, food, or space.
Direct competition in nature often results in a winner
and a loser—with the losing organism failing to
survive.
The principle of competitive exclusion
Aka ‘Gause’s Law’
‘No two species can occupy the
same niche in the same habitat
for a prolonged time’
The Competitive Exclusion Principle
• 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 and Invasive
species…
Invasive Species are those which have been
introduced to a non-native habitat/ecosystem
(usually by human interention). They often outcompete – (and drive towards extinction) – the
native species…
• Grey Squirrels
• Cane toads!
• Zebra Mussels
Competitive
Exclusion:
Squirrels
Competitive Exclusion: Squirrel
Distribution
Competition in the plant world
• Japanese knotweed
• David Attenborough tropical conpetition
Competition can even take place between
species from different kingdoms…
• Spider versus plant
Can species ‘work around’ the
competitive exclusion principle?
Yes they can!: 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
Spatial Niche Partitioning
Closely related
bird species
occupy different
foraging locations
on a single tree
species
Community Interactions
The distribution of these warblers avoids
direct competition, because each species
feeds in a different part of the tree.
Feeding height (m)
18
12
6
0
Cape May Warbler
Bay-Breasted
Warbler
Yellow-Rumped Warbler
Temporal Niche Partitioning
Different species of spiny
mouse inhabiting the
same ecosystem may be
either nocturnal OR
diurnal feeders