Understanding Populations
Chapter 8 p.196- 217
Key Terms
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Populations
Density
Dispersion
Growth rate
Reproductive potential
Exponential growth
Carrying capacity
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Niche
Competition
Predation
Parasitism
Mutualism
Commensalism
Symbiosis
Objectives
• Describe the 3 main properties of a
population
• Describe exponential population growth
• Describe how the reproductive behavior of
individuals can affect the growth rate of their
populations
• Explain how populations sizes in nature are
regulated
What is a Population?
• All the members of a species living in the
same place at the same time.
Properties
1. size2. density- the number of individuals per unit
area or volume
3. Dispersion- is the relative distribution or
arrangement of its individuals within a given
amount of space
Dispersion Patterns
• Within a population’s geographic range, local
densities may vary greatly.
• The dispersion pattern of a population refers to
the way individuals are spaced within their area.
• These patterns are important characteristics for
an ecologist to study, since they provide insights
into the environmental effects and social
interactions in the population.
1. Clumped
2. Uniform
3. Random
Dispersion Patterns
Clumped pattern
– Most common in nature
– Individuals are aggregated in patches
– Often results from an unequal distribution of resources
in the environment.
• For example, plants or fungi may be clumped in areas where
soil conditions and other factors favor germination and growth.
– Clumping of animals is often associated with uneven
food distribution or with mating or other social behavior.
• For example, fish are often clumped in schools, which may
reduce predation risks and increase feeding efficiency.
Mosquitoes often swarm in great numbers, increasing their
chances for mating.
Uniform, or even, pattern
– Pattern of dispersion often results from
interactions between the individuals of a
population.
• For example, some plants secrete chemicals that inhibit
the germination and growth of nearby plants that could
compete for resources.
– Animals may exhibit uniform dispersion as a result
of territorial behavior.
• For example, penguins and humans
Random dispersion
– Individuals in a population are spaced in a
patternless, unpredictable way.
• For example, clams living in a coastal mudflat might be
randomly dispersed at times of the year when they are
not breeding and when resources are plentiful and do
not affect their distribution.
– Varying habitat conditions and social interactions
make random dispersion rare.
How does a Population
Grow?
• Birth rates and death rates  change in rate is
the growth rate
• Can be +, -, or even 0
Equation:
Change in the population size =
Birth rates – Death Rates
(You can also look at immigration and
emigration)
How Fast Can a Population
Grow?
• A female sea turtle can lay 2,000 eggs  many
will die
Reproductive potential- limited buy the number of
offspring an individual can have
– 750 years for a pair of elephants to produce 19 million
decedents
– One bacteria can produce 19 million decedents in a
few days
• Can change or increase based on when
reproduce, how many offspring, how often they
reproduce
• Small organisms short life span high reproduction
rate and vise versa
Exponential Growth
• They grow faster and faster
– Dog has 6 puppies and they each have 6 puppies
and so on
• This can occur if there is plenty of food and
space and there is no competition or
predators
Logistic Growth Model (Carrying Capacity)
– A description of idealized population growth that is slowed by limiting factors
as the population size increases. (can be both abiotic and biotic factors)
• Limiting factors are environmental factors that restrict population growth.
• carrying capacity is the maximum population size that a particular
environment can support or “carry”
– S-shape curve or J- shaped
• 1. Exponential Growth Phase-When the population first starts growing,
population growth is close to exponential growth
• 2. Transitional Phase- The population growth starts to slow
• 3. Plateau Phase- Carrying capacity is reached and the population is as big
as it can theoretically get in its environment
What Limits Population Growth?
• Environments are never constant and populations
cannot grow forever and rarely grow at their
reproductive potential
• Environments can change and resources can be
used up  populations can change over time
1. Carrying Capacity maximum number of a species
that an environment can sustain
• Difficult to determine, often by population
averages or after large population crash
carrying capacity
• In order to determine what a sustainable population level might be, we
need to understand the ecological concept of carrying capacity. Carrying
capacity is the population level of an organism that can be sustained given
the quantity of life supporting infrastructure available to it. If the numbers
of an organism are below the carrying capacity of its environment, its birth
rate will increase. If the population exceeds the carrying capacity, the
death rate will increase until the population numbers are stable. Carrying
capacity can be increased by the discovery and exploitation of new
resources (such as metals, oil or fertile uninhabited land) and it can be
decreased by resource exhaustion and waste buildup, for example
declining soil fertility and water pollution.
Determining Population Growth
Logistic Growth Curves
overshoot
• In ecology, overshoot is said to have occurred
when a population's consumption exceeds the
carrying capacity of its environment, as
illustrated in this graphic:
World Population
• An increase in the carrying capacity of an environment can generally be
inferred from a rise in the population inhabiting it. The stronger the rise,
the more certain we can be that the carrying capacity has expanded. In
our case a graph of world population makes it obvious that something
(OIL) has massively increased the world's carrying capacity in the last 150
years. During the first 1800 years of the Common Era, like the tens of
thousands of years before, the population rose very gradually as humanity
spread across the globe. Around 1800 this began to change, and by 1900
the human population was rising dramatically: What happens when oil
runs out?
What Limits Population Growth?
2. Resource Limits or limiting resource can
determine the carrying capacity
3. Competition within a populationcompetition for the same resources, shelter,
food or breeding sites, predator/ prey
Territory- area defended by one or more
individuals against other s
Limiting factors
Factors that influence an organism into two types
1. Living components- biotic factors
2. Nonliving factors- abiotic factors (changing)
a)
b)
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f)
Temperature
Humidity
pH
Salinity
Oxygen concentrations
Amount of sunlight
Web cd 34 b
Ecology 2010
2 types of Population Regulations
1. Density Dependent – death is a result of over
population
• Competition among members of a growing population for limited
resources, like food or territory.
• Health of organisms
• Predation
• Physiological factors (reproduction, growth, hormone changes)
2. Density Independent- death is a result
regardless of the population size
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Weather conditions
Acidity
Salinity
Fires
Catastrophies
8.2 How Species Interact with Each
Other
• Explain the difference between niche and
habitat
• Give examples of parts of a niche
• Describe the five major types of interactions
between species
• Explain the difference between parasitism and
predation
• Explain how symbiotic relationships my evolve
An Organism’s Niche
• Unique role of a species within an ecosystem
• Physical home, abiotic and biotic factors, but it
is not the same as a habitat which is the
location
• Job or role in ecosystem
Keystone Species
Sometimes changes in the population of a single species, often called a
keystone species, can cause dramatic changes in the structure of a
community.
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In the cold waters off the Pacific coast of North America, for example, sea
otters devour large quantities of sea urchins.
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Urchins are herbivores whose favorite food is kelp, giant algae that grow in
undersea “forests.”
– A century ago, sea otters were nearly eliminated by hunting. Unexpectedly, the
kelp forest nearly vanished.
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Without otters as predators, the sea urchin population skyrocketed, and
armies of urchins devoured kelp down to bare rock.
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Without kelp to provide habitat, many other animals, including seabirds,
disappeared.
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Otters were a keystone species in this community.
Ecology 2010
Species interactions
• Competition- -/– Indirect- use same resources but never actually
occupy same time (night/day) (intraspecific and
interspecific)
– Adaptations (resource partition/ reduced niche)
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Predation- +/Parasitism- +/- (require host to survive)
Mutualism- +/+
Commensalism- +/ 0
Symbiosis and coevolutoin
Types of Competition
1. Interspecific competition- type of interaction in
which two or more species use the same limited
resources (plants and sunlight)
2. Intraspecific competition- same species
Web cd 37 A
3. Competitive exclusion- one species gets eliminated
from the community due to resources
4. Reduce niche size- interactions with other species,
-fundamental- potentially use,
-realized niche- what is actually used
Ecology 2010
Ecology 2010
The Competitive Exclusion
Principle
– The competitive exclusion principle states that no two
species can occupy exactly the same niche in exactly the
same habitat at exactly the same time.
– If two species attempt to occupy the same niche, one
species will be better at competing for limited resources
and will eventually exclude the other species.
– As a result of competitive exclusion, natural communities
rarely have niches that overlap significantly.
Ecology 2010
The Competitive Exclusion Principle
– In the experiment shown in the graph, two species of
paramecia (P. aurelia and P. caudatum) were first
grown in separate cultures (dashed lines) . In separate
cultures, but under the same conditions, both
populations grew. When organism were put in the
same culture one species dies off.
– However, when both species were grown together in
the same culture (solid line), one species
outcompeted the other, and the less competitive
species did not survive.
Ecology 2010
Types of Competition
4. Character displacement- evolution of
differences in a characteristic due to
competition, way to reduce niche overlap,
finches
5. Resource partitioning- when similar species
coexist each species may avoid competition
with others by using a specific part of an
available resource (warbler eating insects at
diff parts of tree)
Ecology 2010
Dividing Resources
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Instead of competing for similar
resources, species usually divide
them.
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For example, the three species of
North American warblers shown all
live in the same trees and feed on
insects.
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But one species feeds on high
branches; another feeds on low
branches, and another feeds in the
middle.
Ecology 2010
Parasitism
Tapeworm in Small Intestine
• A parasite lives on or in its host and obtains its
nourishment from the host.
– For example: A tapeworm is an internal parasite that lives inside
the intestines of a larger animal and absorbs nutrients from its
hosts.
– Another example: Ticks, which suck blood from animals, and
aphids, which tap into the sap of plants, are examples of external
parasites.
• Natural selection favors the parasites that are best able to
find and feed on hosts, and also favors the evolution of
host defenses.
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http://oldnewsbaby.com/site/click/8b0c2347f6ec462a9f82592cb0a664c7
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http://user.it.uu.se/~svens/larverna/normal.html
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http://www.neatorama.com/2006/08/21/six-horrifying-parasites/
Tick on a dog
Commensalism
• One partner benefits without significantly affecting the
other.
• Few cases of absolute commensalism have been
documented, because it is unlikely that one partner will
be completely unaffected.
• For example: algae that grow on the shells of sea
turtles, barnacles that attach to whales, and birds that
feed on insects flushed out of the grass by grazing cattle.
Algae on Sea Turtle
Barnacles on Whale
Mutualism
• Benefits both partners in the relationship.
• For example: the association of legume plants and
nitrogen-fixing bacteria.
– Bacteria turn nitrogen in the air to nitrates that the plants can
use
• Another example: Acacia trees and the predaceous ants
they attract.
– Tree provides room and board for ants
– Ants benefit the tree by attacking virtually anything that touches
it.
Acacia Trees and Ants
Examples
1. Tapeworms live in the intestines of mammals, where they absorb large
amounts of their hosts’ food.
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Fleas, ticks, lice, and the leech shown, live on the bodies of mammals and
feed on their blood and skin.
2. The sea anemone’s sting has two functions: to capture prey and to protect the anemone
from predators. Even so, certain fish manage to snack on anemone tentacles.
The clownfish, however, is immune to anemone stings. When threatened by a predator, clownfish
seek shelter by snuggling deep into an anemone’s tentacles.
3. Barnacles often attach themselves to a whale’s skin. They perform no known service to
the whale, nor do they harm it. Yet the barnacles benefit from the constant movement
of water—that is full of food particles—past the swimming whale.
Ecology 2010
Chapter 9: The Human
Population
P218- 233
Key Terms
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Demography
Age structure
Survivorship
Fertility rate
Migration
Life expectancy
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Demographic transition
Infrastructure
Arable land
Urbanization
Least developed
countries
objectives
• Describe how the size and growth rate of the
human population has changed in the last 200
years
• Define four properties that scientists use to
predict population size
• Make predictions about population trends based
on age structure
• Describe the four stages of the demographic
transition
• Explain why different countries may be at
different stages of the demographic transition
9.1 Studying Human Populations
• How have the human populations changed in
the US in the past 50 years ?
• What problems can occur if human population
growth too rapidly?
9.1 Studying Human Populations
• Populations grew faster in the 20th century that it
has before  leads to environmental problems
• Demography- is the study of populations, but
most often refers to the study of human
populations
• Study historical size and makeup to make
predications
• Economics and social structure that can impact
populations (developed vs. developing)
Human Populations Over Time
• 1800s populations begin to grow
exponential due to increase in food,
medical, hygiene  Earth is reaching it
carrying capacity
Forecasting Population size
• What resources will your community need in
20 years? (schools, retirement communities,
roads, utilities)
• Constant changes due to human behavior
1. Age structure
2. Survivorship
3. Fertility rates
4. Migration/emigration
Age Structure Diagrams
Survivorship curves fit three
types.
Is the percentage of members of a group
that are likely to survive to any given age
1. Type I curve shows a low death rate in early and middle
life but the death rate increases steeply in old age.
Produce few offspring, take care of their young, many
survive into maturity (Japan/ Germany)
2. Type II curve shows a death rate is more constant
throughout the lifetime of the species.
3. Type III high death rates for the very young, mature
individuals survive longer, usually involves very large #
of offspring with little or no parent care
http://www.quia.com/rr/486328.html?AP_rand=59817604
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Questions:
1. Which curve would fit an organism that cares for
its young and reproduces relatively late in life?
Type I
2. Which curve would be typical of an organism
that experiences high predation as small
individuals but when they are adults are more
able to avoid most predators?.
Type III
3. Which curve might best fit rodents that die in
numbers at all ages?
Type II
Declining Death Rates
• Recent years death rates have decreased more
rapidly than birth rates
• Adequate food, clean water, medical and
sanitation
• Life expectancy- average number of years a
person is likely to live (67 years)
The Demographic Transition
• Describes how these changes can occur, based
on observations of history of many developed
countries
• Developed countries stopped growing
• Industrial development causes economic and
social progress that affects pop growth
Stages of the Transition
• 1st- preindustrial condition- BR and DR are both
at high levels and pop size stable
• 2nd- Transitional- pop explosion; death rates
decline and birth rates remain high pop grows
fast
• 3rd- Industrial- pop growth slow; birth rates
decrease; BR close to DR pop stabilizes; pop still
large
• 4th- Postindustrial- BR drops below replacement
level; pop decrease
Stages of Demographic
Transition
Women and Fertility
• Education and economic independence for
women
• Cost of child care; waiting past fertility
• Developed countries  1.6 children
• Developing countries  3.1 children
9.2 Changing Population Trends
• Describe three problems caused by rapid
human population growth
• Compare population growth problems in
more-developed countries and less developed
countries
• Analyze strategies countries may use to
reduce their population growth
• Describe worldwide populations into the next
century
Changing Population Trends
• Populations that have high rates of growth
create environmental problems
• Rapidly growing population uses resources at
an increase rate and can overwhelm the
infrastructure of a community.
• Infrastructure is the basic facilities and
services that support a community, such as
public water supplies, sewer lines, power
plants, roads subways, schools and hospitals
Problems of Rapid Growth
• Limited resources (vegetation, water and land)
• Standards of living can decline
– Shortage of fuelwood
– Unsafe water
– Arable land- used to grow crops
– Urbanization- city living rather than rural
(suburban sprawl)
Demographically Diverse World
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More or less developed
Development is complex and politically sensitive
Modern industries but income low
Stable and educated populations but little
industrialization
• Focus on least developed countries- few signs of
development
• More developed  slow population growth
• Less developed  faster population growth
Managing Development and
Population Growth
• China, Thailand, India campaigns to reduce
the fertility rates of citizens (public
advertising, family planning program,
economic incentives, legal punishments)
• 1994- UN held International Conference on
Population and Development (ICPD)- favor
stabilizing population growth through
investments in development, improvements in
women’s status
Growth is Slowing
• Human pop is 6 billion ww
• Peaked at 87 million people per year between
1985 and 1990
• 1990-1995 pop grew 81 million
• Fertility rates have declined since 1970s
• 2050 predict low fertility rates and world
population of 9 billion
US Fertility Rate
Over