Download Chapter 5 Bio Roche

Chapter 5 & 6
Populations
&
Humans in the Biosphere
Chapter 5
Populations
Copyright Pearson Prentice Hall
Videos
• Quest Video KQED: What’s killing the sea otters
– http://youtu.be/Wcy-i_IJH9Y
• Sea Otters and Kelp
– http://youtu.be/v_aSl3iL7rM
– http://youtu.be/D3W4OCnHyCs
• The science of overpopulation youtube
– http://youtu.be/dD-yN2G5BY0
• 7 billion; how did we get so big so fast youtube
– http://youtu.be/VcSX4ytEfcE
• 2012 wolf population on Isle Royale youtube
– http://youtu.be/HbtbWKKE1tY
– http://youtu.be/PdwnfPurXcs
• Black-Footed Ferrets
– http://youtu.be/LkoCNnV7RFY
What shapes an ecosystem?
•
•
•
•
•
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The Niche
Competition
Exponential growth
Logistic growth
Carrying Capacity
Limiting Factors
5-1
How Populations Grow
Four Important Characteristics of a Population
1. Geographic distribution: the area inhabited
2. Population density: the number of
individuals per unit area
# 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠
=
𝑎𝑟𝑒𝑎
3. Growth rate: change in number of individuals
over time
4. The population’s age structure.
Exponential Growth
Under ideal conditions with unlimited
resources & protection from predators &
disease, a population will grow exponentially
= the biotic potential of a species.
 Individuals in a population reproduce at a
constant rate.
 Population reaches an infinitely large
size.
 Characterized by a J shaped curve.
Exponential Population Growth
Logistic Growth
• In nature, exponential growth does not
continue in a population for very long.
• A population's growth slows or stops
following a period of exponential growth
• The environment reaches its carrying
capacity
1. As resources become less available, the growth
of a population slows or stops.
2. When birthrate decreases, death rate
increases.
3. When immigration decreases, emigration
increases
Logistic growth is characterized by
an S-shaped curve.
Carrying Capacity
–The largest number of individuals that a
given environment can support.
–When a population reaches the carrying
capacity of its environment, its
The growth levels off.
The average growth rate is zero.
• Stop and practice
5-2 Limits to Growth
Limiting Factors
– The primary productivity of an ecosystem
can be reduced when there is an insufficient
supply of a particular nutrient.
– Ecologists call such substances limiting
nutrients.
– A limiting nutrient is an example of a
limiting factor.
– In the context of populations, a limiting
factor causes population growth to decrease.
Copyright Pearson Prentice Hall
Density-Dependent Limiting Factors
 Depend on population size.
 Become limiting if population reaches a
certain size; generally LARGE & DENSE,
not scattered and small
 Include:
1.
2.
3.
4.
Competition
Predation
Parasitism
Disease
Density-Dependent Factors: Competition
• Crowded populations of the same species
compete for food, water, space, sunlight
• Competition can also occur between members
of different species.
– Both species will be under pressure to change in
ways that reduce competition
– This type of competition can lead to evolutionary
change.
– Over time, the species may evolve to occupy
different niches.
Copyright Pearson Prentice Hall
Density-Dependent Factors: Predation
–Populations in nature are often
controlled by predation.
–The regulation of a population by
predation takes place within a predatorprey relationship.
• Example: A small population of wolves controls
the size of a large population of moose.
The gray wolf and moose population
of Michigan’s Isle Royale
• Isle Royale is a small, isolated and remote,
forested island in Lake Superior
• It is uninhabited by humans except for 155
campsite permits each summer
• There is little migration of animals onto the
island
• Here scientists conduct the longest continuous
study of a predator-prey system in the world
Density-Dependent Factors-Predation
Wolf and Moose Populations on Isle Royale
Moose
Wolves
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The predator-prey cycle
• Periodic increases in the moose population
are quickly followed by increases in the wolf
population
• More wolves results in increased predation
• This causes moose population to decline
• Since there are fewer prey the wolf population
declines also
Density-Dependent Factors:
Parasitism and Disease
• The moose population on Isle Royale is
affected by a parasite
• The wolf population on Isle Royale is affected
by a virus introduced by a camper’s dog
Should humans intervene?
• Rolf Peterson, the longest-serving director of wolf-moose
studies on Isle Royale, argued for this view in an op-ed he
coauthored for the New York Times:
• “The future health of Isle Royale will be judged against one
of the most important findings in conservation science: that
a healthy ecosystem depends critically on the presence of
top predators like wolves when large herbivores, like
moose, are present. Without top predators, prey tend to
become overabundant and decimate plants and trees that
many species of birds, mammals and insects depend on.”
• - See more at:
http://blog.nature.org/science/2013/10/10/should-we-letthe-wolves-of-isle-royale-disappear/#sthash.JZOyjq6c.dpuf
Density-independent limiting
factors
• Affect all populations in similar ways, regardless
of the population size.
•Examples:
• unusual weather like drought or hurricanes
• natural disasters
• seasonal cycles
• certain human activities—such as damming
rivers and clear-cutting forests
5-3
Human Population
Growth
Historical Overview
With advances in
sanitation,
agriculture, industry
and medicine, the
human population
experienced
exponential growth.
Demography is the study of populations
• Demography helps to explain the patterns of
population growth and decline
• Birthrates, death rates, and the age structure
help predict the growth rate of countries
• Globally, the growth rate hit a peak in the 60’s
at around 2%
• The current growth rate is around 1%.
– Although declining, any value above zero means that
population continues to grow.
– It is expected to reach 9 billion by 2050.
Patterns of Population Growth
80+
Males
Females
60–64
Age (years)
• In the United
States, there are
nearly equal
numbers of
people in each
age group.
• This age
structure
diagram predicts
a slow but
steady growth
rate for the near
future.
U.S. Population
40–44
20–24
0–4
8 6 4 2 0 2 4 6 8
Percentage of Population
Copyright Pearson Prentice Hall
Patterns of Population Growth
80+
Males
Females
60–64
Age (years)
• In Rwanda, there
are many more
young children
than teenagers,
and many more
teenagers than
adults.
• This age
structure
diagram predicts
a population
that will double
in about 30
years.
Rwandan Population
40–44
20–24
0–4
Percentage of Population
Copyright Pearson Prentice Hall
The Demographic Transition
– Over the past century, population growth in
the United States, Japan, and much of
Europe has slowed dramatically.
– According to demographers, these
countries have completed the demographic
transition, a dramatic change in birth and
death rates.
Three Stages of
Demographic Transition
• Stage 1: both
rates high
• Stage 2: death
rate drops birth
rate high =
population
increases
• Stage 3: birth
rate drops and
population
growth slows
Patterns of Population Growth
• The
demographic
transition is
complete
when the
birthrate falls
to meet the
death rate,
and
population
growth stops.
Copyright Pearson Prentice Hall