Measuring and Modelling Population Change...Survivorship can be graphed to illustrate age at which...
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Part 1 Measuring and Modelling Population Change
Transcript of Measuring and Modelling Population Change...Survivorship can be graphed to illustrate age at which...
Part 1
Measuring and Modelling Population Change
An ecosystem is finite and therefore has a limited supply of biotic and abiotic resources
Carrying capacity - maximum number of organisms that can be sustained by available resources over a given time
Carrying capacity is dynamic (always changing) since environmental conditions are always changing
Population Dynamics - changes in population's characteristics over a period of time
Main factors that influence populations are:
natality (number of births)mortality (number of deaths)immigration (number that enter population)emigration (number that leave population)
= (birth + immigration) - (deaths + emigration)Population
Change
Survivorship can be graphed to illustrate age at which individuals within species die
3 general patterns in survivorship of species:
Num
ber
of s
urvi
vors
Age Age
Num
ber
of s
urvi
vors
AgeN
umbe
r of
sur
vivo
rs
Type IPopulations show high survivorship
until late in life
Type IIPopulations show a fairly constant
rate of death
Type IIIPopulations show
lowest survivorship early in life
[(births + immigration)
Growth rate - percentage change in a population in a given time period
Population Growth Rate = (deaths + emigration)]−
X 100
Individuals gained
Individuals lost
−
Initial population size (n)
Population Growth ModelsIn situations where a population is well under its carrying capacity its size can continue to increase at a constant rate that can be calculated
If population only reproduces during a breeding season it will show geometric growth
If population breeds continuously it will show
exponential growth
Population Growth ModelsRate of geometric growth (λ) is given by equation:
N(t)
N(t + 1)=
Rate of exponential growth is given by equation:
dNdt = rN
N(t) = pop. size at time t
N (t + 1) = pop. size at a later time
r = per capita growth rate
N = population size
λ
Yeast cells
0
4
8
12
16
20
24
28
0 1 2 3 4 5 6 70
2 000
4 000
6 000
8 000
10 000
0 1 2 3 4 5
Geometric Growth
White tailed deer
Births in breeding season
Deaths between seasons
Time (years)
Pop
ulat
ion
siz
eExponential Growth
Time (days)
Pop
ulat
ion
siz
e (x
100
0)
For any population growing exponentially, time needed to double is constant
Following formula gives useful approximation of doubling time (td) when value “r” is known:
Population Growth Models
td =0.69
r
