Interaction in Ecosystems
Symbiotic Relationships
“a set of relationships between
individuals of different species”
3 types of symbiotic relationship
Symbiotic Relationships
Parasitism
Commensalism
Mutualism
Parasitism
-where one partner (the parasite) benefits
and the other is harmed (the host).
Parasites may be:
• obligate (ie completely dependent on the host)
• facultative (ie can survive without the host)
Parasites may be…..
...endoparasites,
which live inside
the body of the
host.
They tend not to kill
their host.
Example:
Tapeworm
Parasites may be…..
• …….. ectoparasites,
which live on the
outside of the
host.
Example:
Fleas
Transmission of Parasites to New Hosts.
Method 1
• Direct contact
eg head lice
Transmission of Parasites to New Hosts.
Method 2
• Resistant stages
eg liver fluke larvae
Transmission of Parasites to New Hosts.
Method 3
• Vectors and
secondary hosts
eg cat tape worms and mice.
•
The eggs of a tapeworm living in
the gut of a cat passes its eggs
with the cat faeces. These may
fall amongst grain which the
mouse inadvertently eats. The
eggs hatch into larvae inside the
mouse which if eaten by a cat
starts the process all over again.
Parasitism
Further Reading
• Environmental Biology Monograph
pages 20/21
• DART Environmental Biology Notes
pages 32/33
• Trials of Life by David Attenborough
pages 176 - 184
Commensalism
• ‘one partner benefits whilst the
other remains unaffected’
• The relationship is usually based on
feeding and/or protection.
Commensalism
Example 1
• Shark and Remora.
The Remora feeds on
scraps out of the
shark’s mouth. The
shark gets no
benefit or harm.
Commensalism
Example 2
• eg two toed sloth and
slothy moths. The
moths get a free ride
to find mates and lay
their eggs in the
droppings of the sloth.
When the caterpillar
hatches it feeds on
the droppings. The
sloth is unaffected.
Commensalism
Further Reading
• Environmental Biology Monograph,
page 21
• DART Environmental Biology Notes,
page 34
• Trials of Life by David Attenborough,
pages 170 - 173
Mutualism
• ‘where both partners benefit.’
• Very common
• Often involves exchange of metabolic
products
• Often close structural compatability
Mutualism
Example 1
Eg Warthog and
oxpecker.
The oxpecker gets a
supply of food and
the warthog gets
rid of parasitic
ticks.
Mutualism
Example 2
• Eg leguminous
plants and
Rhizobium bacteria.
• The plant gets a
supply of nitrate
and the Rhizobium
gets provided with
leg-haemoglobin to
limit oxygen supply.
Mutualism
Example 3
• eg sloths and algae.
• The algae provides
camouflage--giving the
sloth a greenish tinge to
match tree foliage. It also
provide nutrients, which
the sloth eats by licking or
is absorbed directly
through the skin.
• The algae are provided
with a habitat and moisture
when the sloth licks the
skin
Mutualism
Further Reading
• Environmental Biology Monograph,
page 22
• DART Environmental Biology Notes,
pages 35 – 36
• Trials of Life by David Attenborough,
chapter 7 ‘Living Together’
• Animal Watching by Desmond Morris,
chapter titled ‘Mutual Aid’
Symbiotic Relationships
• Now watch the ‘Weird Nature’ video
titled ‘Relationships’