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GRADE 11/12 POPULATION ECOLOGY SUMMARY
In this document, I summarized the topic of population ecology in an easier way to understand for exams. (IEB syllabus)
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Population Ecology : section 1 population size-
a population : is the total number of individuals of the same species that occupy a specific area & that are able to interbreed at a
specific time .
I
species :
a
group of closely related
organisms that can interbreed & produce fertile offspring .
'
population ecology : the
study of populations .
Characteristics of a population :
1.
density
:
the number of individuals per unit area or unit volume .
2. sex ratios :
the ratio of male
& female individuals within the population .
3. pattern of distribution :
this refers to how the individuals of a
population are distributed over the area that the
occupy .
distribution
may be random ; clumped or uniform ) .
1
Population parameters
: a factor that determines the size of a population § the changes that occur to the size of the
population over time .
i. birth rate natality
: the rate at which new individuals are added to a population through reproduction .
2. death rate
morality
:
the rate at which new individuals are lost to a population from somewhere else .
3.
immigration : the rate at which new individuals join a
population from somewhere else .
the from
4. emigration which individuals population it to somewhere else
:
rate at leave
a
go
.
Rate of
Change ( bir thrate +
immigration rate death rate +
emigration rate .
Measuring the size of a population :
'
Counting :
direct method c. traps :
capture small animals in a habitat .
'
organisms must be visible d. direct observation : walk around an
ecosystem and record
•
be reasonably large the different species
-
must stand still field
e.
guides :
these are books are used for identifying
2 all the plants & animals that you find
Sampling
.
: indirect method
f. mark and recapture :
used to measure the size of a population
quadrants square frame that
- -
a. : a has a known area .
i.
population size = 1 . the number of animals from a population is captured
average number per quad ✗ Surface Area of area z .
they are marked in some way & then released
surface Area of quad
3 time later another of animals from the same
not reliable .
. some group
,
b. transects : a line formed by a tape / rope stretched across a
population captured ( recaptures from
is . 1st
sampling ) .
s
part of
ecosystem being investigated .
As
you walk
along rope 4 .
the number of marked animals is counted
you record the species you found § it's position .
, example of quadrant sampling method
:
using the
Farm
'
i
'
f
' -
' ' -
> -
.
i -
'
¥
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Ave
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-
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-
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i • -
=
4 per
.
/ m2 quad
.
. ,
. , .
' ' - '
- '
;
-
/ '
' '
;
.
.
.
•
'
4-
'
10m population size SA of
per quad
.
-
.
u
'
.
.
=
average no ,
✗ area
-
c-
'
i '
quad
- '
i. , \
" "
n SA of .
< < - ' e
' - <
, i ,
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i
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: ::: : i :-.
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i :S: : :-. =
4 ✗
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i n
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, u
=
400 Sunflowers
,
e -.
10m
Population size No .
of 1st sample ✗ no . in 2nd sample
example of the mark & recapture method : no . of marked individuals in 2nd sample
Day 1
r
"
r
m,
,
,
Population size =
1
"
1
. i
m : no . in sample 1
Day 2
n : no . in sample 2
1- :
no . of individuals marked in sample 2 .
/
,
P
'
. .
= 10 ✗ 10 -
4 -
= 25 turtles .
Limiting factors :
factor that limits the rate of population growth .
i.e Food dec dec !
population inc population will
' -
as a
(
. .
. .
'
i. e competition ,
predation & diseases =
density -
dependent factors
-
density
-
dependent factors :
Factor that has a
greater & greater effect on a population as the population increases in size .
'
i. e earthquakes ,
flood & fires =
density -
independent factors
( doesn't matter how
big the population is .
the maximum support for indefinite period of time
Carrying capacity number of individuals of population that
ecosystem
:
a can an
•
environmental resistance the combined effect of limiting factors that limit the of population
growth
:
all a .
it causes the / immigration to dec Resulting in balance
'
birth rate a
When population reaches
carrying capacity
.
a
. .
,
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