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Populations of different species =
COMMUNITY
This illustration presents a community of interacting living and
non-living organisms. Producers, consumers, decomposers, and
abiotic matter form an integrated, functioning whole driven by the
sun’s energy.
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consists of populations of different species (plants
and animals) living and interacting in the same place
at the same time.
− This populations/organisms depend on one
another.
− The composition of community is called
community structure (animals and plants)
− The relative abundance of any other species can
affect the abundance/number of other species,
− And thus alter community structure in an
ecosystem
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Flow of Energy in an Ecosystem
The sun is the original source of energy in an ecosystem.. Since energy is
lost in each step, populations are necessarily smaller at each higher level
of the pyramid.
Five Main Types of Interactions in a
Community
− Populations of a community interact
and affect one another in a variety of
ways.
− The interaction can either be harmful or
beneficial to organisms involved.
−The interactions are:o Predation
o Mutualism
o Competition
o Parasitism
o Commensalism
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KNOW FOR THIS SECTION!!!
• Name of interaction
• Definition
• South African e.g.
Species that captures, kill and eat other species – predation
Lionesses hunt in teams to bring down
large animals such as the buffalo in this
picture
An African fish eagle flies off from the
surface of the Okavango River, Botswana,
clutching a tiger fish
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PREDATION
− Predation is the feeding interaction
between the predator and prey.
− The predator is an animal that
hunt, capture and kill other animals
(prey) for
food.
− The prey is the animal being
hunted and killed.
− In this way the number of prey
might fluctuate(because of
availability of
food, shelter, etc).
− This in turn causes a
corresponding fluctuation in
predators.
Predation is a density-dependent factor
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Predatorprey
relationships
pg 296-297
ACT 3.2.2 pg 298 no 1 only
Species may compete for various resource
Competition
− Occurs when a large number of organisms depend on a
common source that
is in short supply.
− Competition (plants)
− can be for :- light
:- water minerals
:- space
:- food (animals)
:- nesting/shelter/space
:- mating partners
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Within
Species
1. Intraspecific competition: the competition
between organisms of the same species
depending on the same resources like food,
space, shelter, water and access to mates.
Between
Species
2. Interspecific competition: the competition
between organisms of different species
depending on the same resources e.g. light,
space, water, shelter, food
Competition: Intraspecific competition
Intraspecific competition: males
compete for territory.
Gemsbuck fighting for mating partners
Interspecific
competition:
In the African
savanna, hyenas
and vultures
compete with
one another for
the flesh of dead
animals such as
the dead
elephant
pictured here.
Interspecific competition
Lion and hyenas fighting for the same food
resources
Jackal and a hyena fighting for the
same food source
In plants competition for light in tropical forests,
o Tall trees extend above canopy
forming umbrella-shape.
o Coniferous trees (lacking broad
leaves absorb pale light.
o Vines (which have their roots in
soil), epiphytes (climbers), climb
on tall trees to reach light
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1. Competitive exclusion: the competition in
which one of the two competing species is much
more successful that the other such that the
successful species survives and the other species
disappears.
Competitive
exclusion
Paramecium aurelia and P. caudatum:
In a classic study in the 1930’s, Gauss
cultured P. aurelia and P. caudatum bot
h alone and together in culture
tubes. When grown separately, the
populations grew to a fairly predictable
density. However, when grown
together, P. caudatum always lost and
eventually went extinct.
Resource partitioning
2. Resource partitioning: The kind of
competition situation in which competing
species coexist in the same habitat since they
use the resources slightly differently
Resource partitioning amongst plants
Different species
of plants in the
same habitat will
compete for the
same resources
like light, water,
mineral salts, etc.
Different species
of plants grow to
different heights
or have roots that
are different
lengths so they
divide the
resources,
accessing them in
slightly different
ways
Resource partitioning: co-existing
shore birds
Specialisation of the Galapagos
finches
Resource partitioning
amongst animals
Resource
partitioning is a
kind of
competition
situation in which
competing
species coexist in
the same habitat
since they use
the resources
slightly differently
Symbiosis
Together
living
• A close interaction between two organisms
such that at least one benefits.
Symbiosis
Individuals of two or more species live in direct and intimate relationships. Required
for survival by one or both species
Mutualism
Commensalism
Parasitism
Obligatory.
One species benefits; the
other species is not
harmed.
Parasite is dependent and
benefits; Host is harmed
Both species benefit.
Examples:
Examples:
*Animals:Birds and
grazing animals
*Plants: Bees and
flowers
*Animals: Barnacles on
whales
*Plants: Epiphytes
growing on trees
Examples:
*Animals:Ticks on grazers
*Plants:Dodder on
angiosperms
a relationship in which one of the species (parasite)
benefits and the other (host) is harmed by the relationship
Parasitism: malaria mosquito
sucking human blood
Life cycle of
the malaria
mosquito
Parasitism: Ticks feeding on animals or humans
A tick bite can cause tick bite fever in humans
Parasitism: swimming habits may influence
parasitic infections
World distribution of
bilharzia
Sanitation
may
influence
parasitic
infections
Platyhelminthes: taenia
solium/tapeworm
Tapeworm with hooks with which it attach to
the wall of the small intestine
Life cycle of a tapeworm
.
Fish Louse
The fish louse, Anilocra capensis, is parasitic on fish. Fish lice chew on
the surface flesh and inflict wounds that can become infected, eventually
resulting in the death of the host
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Mutualism
The symbiotic relationship in which both
of the species benefit from the
association.
Mutualism: oxpeckers on a giraffe. The oxpecker
gets food from the giraffe and the giraffe benefits
by getting rid of its parasites
Mutualism: Lichens is an organism made up of fungi
and algae. The fungus provides the external structure
of the lichen and provides the algae with a protected
place to live. Algae photosynthesise and provide the
fungus with food.
Bacteria and roots of leguminous plants (e.g.
soybeans, beans)
o Bacteria convert nitrogen to
nitrate and ammonium.
o Plants use nitrate and
ammonium for acid and
protein productions.
o Bacteria get carbohydrates
(food) from plants.
o In this way both organisms
(bacteria and plants) benefit
from the relationship.
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Bees collect pollen and nectar from
flowers, flowers are pollinated in
the process
Ants get nectar from the Acacia tree as well as
shelter in specialised swollen thorns. Ants
defend the tree against herbivorous and wood
boring insects.
Commensalism
Two species living together where one
species benefits and the other neither
benefits nor suffers any disadvantage
The egret catch insects which are disturbed by the
activity of a large animal. The herbivore are neither
helped nor harmed by the egret
Whale and barnacles
•Barnacles are attached to skin of whales.
•In this way are moved around to get fresh foods.
•Without spending more energy.
•The whale is not harmed nor benefit from the association
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Remora fish swim next to sharks or attach to
them. It gets protection and scraps of leftover
food from the shark. The shark is neither helped
nor harmed by the remora fish
Human influence on community
structure
The elephant herd in the Kruger National Park
increased from 8, 000 to 12,500 in 2008 and to
19 000 in 2009. The elephant population is
increasing by 7% per year, and might reach 20 000
by 2012. This large herd cannot be sustained since
adult elephants consume 130 kg food a day and
they live for 55 – 65 years.
On 25 February 2008 the SA Government finally
concluded it would have to lift a 17 year-old
moratorium on the culling of the native elephant to
cope with its booming population. Minister van
Schalkwyk announced that killing of excess animals
would only be allowed once all other options
(translocation and contraception) had been ruled
out.
Minister van Schalkwyk said:”Our simple reality is
that elephant population density has risen so
mulch in some southern African countries that
there is concern about impacts on the landscape,
the viability of other species and the livelihoods
and safety of people living within elephant ranges.”
The aesthetic value
placed on South Africa’s
biodiversity.
Discuss the values placed
on “large and fury’ animals
compared to “small and
slimy” animals
1. Which of these animals
will attract most tourists?
‘Small and
slimy” can
be very
interesting.
Community changes over
time
Forest before Forest after
Definition of Ecological
succession
• Succession is a process of ecological
change in which a series of natural
communities are established and then
replaced over time.
• Natural, gradual changes in the types of
species that live in an area.
Terminology
1. Pioneer plant: a plant that can colonise bare soil and that
is part of the community that forms the first stage in the
process of succession
2. Climax community: the final stage in the process of
succession that refers to a mature community of plants
that will remain stable with few, if any, changes over time
3. Primary succession: the sequence of organisms that
occupy a new habitat. (a place without soil)
4. Secondary succession: the sequence of organisms that
occupy a disturbed habitat (where soil exists) or when an
established community has been disturbed in a
catastrophic manner.
The chart below shows primary succession
that results in a forest community
Succession of plant species on
abandoned field
Pioneer species
A group of organisms, such as lichens,
found in the primary stage of succession
and that begin an area's soil-building
process
Succession
Primary succession begins in areas
consisting of bare, lifeless substrate such as
rocks or a car path. Organisms gradually
move into the area and begin to change its
nature,
Secondary succession occurs when a established
community has been disturbed in a catastrophic
manner, e.g. after a veld fire or a flood. In the
disturbance all the vegetation is destroyed, but all
or some of the soil remains. The same process
occurs as in primary succession, but as there is
soil for grasses and small plants to grow in, these
plants form the pioneer communities.
Pioneer plants
Lichens are pioneer plants as they are the first
organisms to colonise a bare area. Acidic
secretions from the lichens help to break down
the hard surface of the rocks and slowly bits of
soil accumulate, mosses may grow on these
small pockets of soil, enriching the quality and
quantity of the soil with the organic material
that they add to it. As time passes and the soil
becomes richer and deeper, other plants like
grasses and small herbaceous plants become
established in the larger pockets of soil , small
animals may also move into an area when
these plants become established.
An example of primary succession
Pioneer grass on a sand dune
Climax community
Secondary succession cont.
• Secondary succession arises on sites where the
vegetation cover has been disturbed by humans
or other animals (an abandoned crop field or cutover forest, or natural forces such as water, wind
storms, and floods.)
• Secondary succession is usually more rapid as
the colonizing area is rich in leftover soil, organic
matter and seeds of the previous vegetation.
Example of secondary succession
Secondary
succession occurs in
an area where life
once existed but has
then been destroyed.
Diagram 1
shows a climax
forest,
Diagram 2
Forest destroyed by
wildfire and
(3 and 4) its
eventual recovery.