more sciencebitz resources on iTunesU and iBooks https://itunesu.itunes.apple.com/enroll/DEZ-HWS-HNJ https://itun.es/gb/ymzI6.n

1. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
All the organisms in any ecosystem
have some effect on every other
organism in that ecosystem.
Also any resource in any ecosystem
exists only in a limited supply.
When these two conditions apply
jointly, competition takes place.

2. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
Competition between members of
the same species:
INTRASPECIFIC COMPETITION

3. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
In a Gannet colony on an
oceanic outcrop, as the
population grows, so the
pressure for good nesting sites
increases
This can affect the number of
eggs that each female can
successfully hatch, and so
affects the birth rate of the
population as a whole.

4. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
Some species deal with
intraspecific competition by
being territorial.

5. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
Or through display

6. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Population growth over time
Competition 700
Intraspecific
competition leads to 525
Population
logistic population
growth 350
175
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Time

7. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
Competition between members of
different species:
INTERSPECIFIC COMPETITION

8. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
The amount of competition depends
on how much each species need for
the resource overlaps:
Species 1 Species 2 Species 1 Species 2
Resource Overlap Resource Overlap

9. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Intraspecific Competition Greater than
Competition 1,000
Interspecific Competition
Carrying Capacity -Theoretical Maximum Population Size
Interspecific competition
may result in a balance, in 800
which both species share
Species 1
Species 2
the resource. 600
400
But with the population
size of each species
200
reduced compared to
without competition
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

10. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Interspecific Competition Greater than
Competition 750
Intraspecific Competition
Carrying Capacity -Theoretical Maximum Population Size
The other outcome is that
one species may totally 600
out compete the other.
Species 1
Species 2
450
This is the principal of
300
competitive exclusion
150
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

11. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
In a woodland plant
species compete for light
Trees should be able to
out compete any smaller
plants

12. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
In deciduous woodland
snowdrops, primroses and
bluebells get around this
problem
They cary out their life
cycle when the bigger
trees and shrubs have no
or few leaves
In spring

13. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Competition
Interspecific competition
is very difficult to show in
the wild
One example may be Red
and Grey Squirrels in
Britain

14. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Sciurus vulgaris = Red Squirrel
Red Squirrels are redder
in the summer, and in
Britain they develop a
white tail in summer
Sometimes the Red
Squirrel goes slightly grey
in the winter making it
difficult to recognise

15. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Sciurus carolinensis = Grey Squirrel
The Grey Squirrel is a
native of eastern North
America
Grey Squirrels sometimes
have ginger hair on their
faces and hands; they
always have white fringes
on their tails

16. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Where it all began.
In 1870 a small number of Grey Squirrels were
brought over to Cheshire (Henbury). They were
subsequently released at a further 28 major sites
across the UK.
Given the numbers of squirrels that were released,
the Grey Squirrel did particularly well. They started
to spread further over the years, venturing further
east, west and north.

17. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Where it all began.
In some areas such as a site in Ireland, the squirrels
couldn't spread quickly due to the poor quality of
woodland.
As the Grey Squirrel spread, the Red Squirrel
retreated. That retreat has continued. Today, Red
Squirrels are very thinly distributed: on the Isle of
Wight, in Scotland and the North of England.

18. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Why is the Red Squirrel declining as the Grey
extends its range?...
• Red-Grey competition?
• Loss of woodland? Not possible as this would
cause both to retreat.
• A disease exists that is more infective to Reds than
Greys?

19. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Red-Grey competition
• there could be a direct antagonism between Red
and Grey Squirrels
• there could be competition for food between Red
and Grey Squirrels
• Grey Squirrels may have a faster reproduction rate

20. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
Records of squirrel sightings in Norfolk between 1960
and 1981 were relied upon to compile this review. At
the start there were Red Squirrels around and no few
Greys.

21. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
1964 - The first sightings of Grey Squirrels were recorded.
1968 - More Grey Squirrels were recorded as being sighted.
1969 - Grey squirrels began consolidating in the south west corner of Norfolk.
1972 - The first losses of Red Squirrels became apparent.
1976 - Red squirrel decline
1981 - Red Squirrels present in the minority

22. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
Over the 20 year period the Red Squirrels were almost all
replaced by Greys.
There were some squares in the study in which Reds were lost but
Greys were never recorded. This suggests there could not have
been a direct antagonism. Also it evidently took up to 16 years for
the Greys to take over, which implies slow ecological competition,
not direct antagonism, at work.

23. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
The Parapox Virus...
• this virus is similar to myxomatosis, but affects Red Squirrels
rather than Rabbits
• its records go as far back as 1227
• there is no evidence of a peak in this disease amongst Red
Squirrels at the time when the Grey Squirrels spread

24. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
Diet...
• Grey Squirrels can digest acorns well, Red Squirrels cannot. Fed
acorns, Red Squirrels lost weight, and only digested 10% of their
polyphenols, while Grey Squirrels maintained weight, and
digested 60% of the polyphenols.
• Red Squirrels are conifer specialists - Pine cones take two years to
mature, so are available in the canopy all year, whereas acorns fall
to the ground each autumn, and have to be collected and stored
there.

25. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
Diet...
• Red Squirrels are light,
and spend most of their
time in the canopy. Grey
Squirrels are heavier, and
spend much time on the
ground.

26. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Reynolds, 1985, Journal of Animal Ecology;56
The Conclusion...
It is still unknown exactly how and why the Grey Squirrel 'takes
over' the Red. It is thought however to be due to slow
competition and ecological differences. There is no evidence to
suggest that Grey Squirrels breed faster than Reds. The
removal of Grey Squirrels on Anglesey has allowed the Red
Squirrels to breed and the young to survive, emphasizing that it
is the presence of Grey squirrels that is the real problem for
Red Squirrels.

27. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Predator Prey relationships
The balance between the
population size of a prey
species and that of its predator.
Populations of predators and
prey are linked.
Include both carnivore and
herbivore relationships.

28. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Predator Prey relationships
80
Number of pelts (1000s)
60
40
Prey population Prey population falls
grows
20
More food Less food
Less hunting More hunting
0
1900 1905 1910 1915 1920
Predator population Predator population Year
falls grows
Snowshoe Hare Lynx

29. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Parasitism
Special case of predation;
the main difference being
that the predator (parasite)
coexists with the prey
(host), rather than killing it.

30. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Parasitism
Endoparasite - lives
inside the body of the
host

31. Topic 2: Ecosystems
2.1.10: Describe and explain population interactions using examples of named
species
Parasitism
Ectoparasite - live on
the body of the host.