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Recap:
Net reproductive rate, R0 --- approximately the # of
female offspring per female per unit time
Intrinsic rate of Increase, r --- natural log of R0
divided by generation time
Section 4
S i Professor Donald McFarlane
dN/dt = r N
EXPONENTIAL GROWTH
Lecture 19 Ecology:
Human Population
Recap:
Carrying capacity, K, is the population size that can
be supported by the environment, indefinitely
K will limit population growth by modifying the
Exponential growth equation
dN/dt = r N(k-N)
K….
LOGISTIC GROWTH….
„
Life history strategies
… Continuum
… r-selected
species – high rate of per capita
population growth, r, but poor competitive
ability (weeds)
… K-selected species – more or less stable
populations adapted to exist at or near
carrying capacity, K
„
Lower reproductive rate but better competitors
(trees)
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r
k
5
6
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8
Human population growth
Popula
ation (billions)
7
In 2006, the world’s population was
estimated to be increasing at the rate of
146 people every minute
„ 2 in developed nations and 144 in less
developed nations
„ Human growth fits an exponential pattern
„
until agriculture and animal
domestication
… Between 1750 and 1998, population surged
from 800 million to 6 billion
6
2000
1992 – 5.44 billion
5
4
3
2
1
… Low
April 2011 – 6.88 billion
1850 – 1.2 billion
1975
Black Death – 14th C
1950
1900
1800
0
7
8
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„
1.
Human populations can exist at equilibrium
densities in one of two ways
High birth and high death rates
„
2.
B f
Before
1750,
1750 thi
this was often
ft th
the case, with
ith high
hi h bi
birth
th
rates offset by deaths from wars, famines, and
epidemics
Low birth and low death rates
„
In Europe, beginning in the 18th century, better
health and living conditions reduced the death rate
„ Eventually, social changes such as increasing
education for women and marriage at a later age
reduced the birth rate
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10
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11
Stage 1
Stage 2
Stage 3
Stage 4
Relative
population
size
High birth rate
High death rate
Birth rate
decreases
Death rate
decreases
Death rate
Low
r
Birth rate
Low birth rate
Low death rate
Relative po
opulation size
Demographic transition
… Shift in birth and death rates with
development
… First stage - birth and death rates are both
high, and the population remains in
equilibrium
… Second stage - death rate declines first
first, while
the birth rate remains high - high rates of
population growth result
… Third stage - birth rates drop and death rates
stabilize, so that population growth slows
… Fourth stage - both birth and death rates are
low, and the population is again at equilibrium
Birth and death rates
„
Relative population size
Increasing Maximal Decreasing
r
Low
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„
Age structure
… Relative
numbers of individuals in each
defined age
g g
group
p
… Commonly displayed as population pyramid
… Helps predict future population growth
„
Exact pace varies between countries depending
on culture, economics, politics, and religion
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14
„
Earth’s carrying capacity
… Many
and varied estimates
… Lifestyle has a huge influence
… Total fertility rate – average number of live
births a woman has during her lifetime
Global TFR declined from 4.47 in 1970s to 2.59 in
2007
„ 2.3 needed for zero population growth (2.1
industrialized)
„ Differs considerably between geographic areas
„ In developed nations, population has stabilized
„ In developing countries, population is still
increasing dramatically
„
15
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
6.7
4.7
North
America 5.0
1.5
Europe
2.3
24
2.4
A i
Asia
Africa
Latin America
& Caribbean
1970–1975
5.0
3.2
2.3
10
TFR of 2.5 (high)
TFR of 2.0 (medium)
TFR of 1.5 (low)
10.8
9.2
9
8
7.8
7
Oceania
6
2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050
Year
2005
17
„
Populatio
on (billions)
2.2
2.0 2.0
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18
Ecological footprint
… Aggregate
total of productive land needed for
survival in a sustainable world
… Average footprint size is about 3 hectares
(1ha=10,000 m2)
… Wide variation is found around the globe
„
7.5 for Canadians, 10 for Americans
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20
5