Download biotic_interactions

Interaction in Ecosystems
Biotic Interactions
2.
Symbiotic Relationships
3.
The costs, benefits and
consequences of interactions
1.
Biotic Interactions
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Introduction
Predation
Grazing
Competition
Introduction
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Abiotic components – conditions and nonliving resources in a particular habitat
e.g.
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Biotic components – are the living aspects in
an ecosystem
e.g.
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Density independent factors affect population
regardless of its size
Density dependent factors affect population
depending on its size.
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Usually when the population number is high,
these factors act to reduce the population
Biotic Interactions
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Interspecific interactions – between members
of different species
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Intraspecific interactions – between members
of the same species
Predation
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Predation is a biotic relationship in which one
species kills and eats another (the prey)
In nature predator – prey interactions are
frequently cyclic
The cyclical nature is due to population
densities of the predators and the prey
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This in turn affects the population densities
The cycle is actually driven by other interactions
(both density dependent and density
independent)
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Draw a predator – prey cycle
Describe its features
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How can predation be useful to prey?
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Predation cont…
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Predation creates diversity in an ecosystem,
by reducing the dominance of one species
and allowing weaker competitors to survive
It reduces prey density and therefore density
dependent factors in the prey species
It drives evolution as prey species adapt to
avoid predation, and predators change
according to the prey
Prey defences
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Camouflage (crypsis ) – blending with the
environment
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Disruptive colouration – markings to break the
body’s outline
Other examples include countershading,
transparency and colour change
Behaviour, such as staying still or choosing a
background to hide, helps.
Prey defences cont…
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Warning (aposematic) colouration – adoption
of bright colours and patterns by dangerous /
inedible species to warn of their danger to
others
Prey defences cont….
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Mullerian mimicry – where one species
resembles another and both species are
dangerous / inedible to predators
Prey defences
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Batesian mimicry – where one harmless / edible
species resembles one that is dangerous /
inedible
Grazing
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Grazing is a form of predation, except only
part of the prey item is consumed at any one
time
Grazing cont…
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In a plant community grazers have two important
effects:
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Maintain species diversity – by keeping dominant grasses
under control more delicate species are able to compete
more effectively
Prevent succession, therefore a climax community is not
reached – grazers eat the apical meristems of woodland
plants, preventing grow. The basal meristems of grasses
are able to withstand grazing. As a result important
habitats and niches are often maintained for a number of
species
Niches
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What do we understand by the term ‘niche’?
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A niche is the functional position of an organism in
the environment. To describe a niche of an
organism detail such as:
Habitat
 Resources obtained (such as food)
 Periods of time it is active
 Physical adaptations
Must be discussed
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Niche cont…
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Fundamental niche – the niche an organism
can potentially occupy under ideal conditions
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Realised niche – the niche an organism
actually occupies due to competition
Competition
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Competition is two or more organisms requiring the
same resource, which is in short supply
Exploitation competition – one species has the
ability to exploit the resource more effectively than
another species
e.g. one species might be faster at obtaining the
resource
Interference competition – one species prevents
another species from obtaining the resource
e.g. by territorial behaviour
Competitive exclusion
principle
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Gause’s principle
No two species with identical (or similar)
niches can coexist for indefinite periods of
time. Eventually one species will be
excluded by the other as a result of
interspecific competition
Resource Partitioning
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Resource partitioning – the dividing up of the
use of each resource by species
specialisation and adaptation
Resource partitioning is a consequence of
overlapping niches. Each species adapts to
exploit different components of a resource
Exotic species
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Species introduced to an ecosystem often out
compete native species
These species often occupy the same niche
as native species, but lack the competitors /
predators found in its natural environment.
With out these checks and balances the
exotic species can dominate the environment
Weaker Competitors
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It is important to ensure the survival of
weaker competitors to maintain species
diversity
Species diversity is important for an
ecosystem to respond to changing conditions
– in one set of conditions a species may be a
weak competitor, but in another set it may be
more dominant organism in an ecosystem
Learning Activities
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Read DART pg 21 – 31
Read Monograph pg 15 – 19
Scholar – all of section 3
Find examples of each of the concepts
discussed.
Barlow’s Brain Buster Questions
Worksheets
Create a concept map linking ideas of
competition and niches