Transcript Population size

Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 40
Population Ecology
© Cengage Learning 2015
© Cengage Learning 2015
The biosphere is
the global
ecosystem, the
sum of all the
planet’s
ecosystems or all
of life and where
it lives.
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© Cengage Learning 2015
40.1 How Do We Describe Populations?
• Ecological factors affect the size, density,
distribution, and age structure of a
population
• Studying population ecology often involves
the use of demographics, which often
change over time
• Demographics
– Statistics that describe a population
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How Do We Describe Populations?
• Biologists frequently use sampling
techniques to estimate population size
– Plot sampling estimates the total number of
individuals in an area based on direct counts
in a small portion of that area
– Estimates from plot sampling are most
accurate when the organisms counted are not
very mobile and conditions across the area
they occupy are more or less uniform
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How Do We Describe Populations?
• Population density
– Number of individuals per unit area or volume
– Example: Number of dandelions per square
meter of lawn
• Population distribution
– Describes how individuals are distributed
– Individuals may be clumped, uniformly
dispersed, or randomly dispersed in an area
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Figure 19.1
How Do We Describe Populations?
• Scientists use mark-recapture sampling to
estimate the population size of mobile
animals, such as Florida Key deer
• Mark-recapture sampling
– Method of estimating population size of
mobile animals by marking individuals,
releasing them, then checking the proportion
of marks among individuals recaptured at a
later time
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40.2 Why Does the Size of a Population
Change?
• Immigration
– Movement of individuals into a population
– Population increases
• Emigration
– Movement of individuals out of a population
– Population decreases
• Zero population growth
– Interval in which births equal deaths
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Why Does the Size of a Population
Change?
• Biotic potential
– Maximum possible population growth rate
under optimal conditions
– Under ideal conditions (shelter, food, and
other essential resources are unlimited, no
predators or pathogens) a population’s growth
rate reaches its biotic potential
– Microbes have high biotic potentials
– Large-bodied mammals have low biotic
potentials
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Why Does the Size of a Population
Change?
Exponential
Growth
Curve
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Why Does the Size of a Population
Change?
Exponential Growth Curve
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40.3 What Constrains Population Growth?
• Limiting factors
– A necessary resource, the depletion of which
halts population growth
– Populations seldom reach their biotic potential
because of the effects of limiting factors
– Not always easy to identify all the factors that
can restrict population growth
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What Constrains Population Growth?
• Limiting factors
– Examples: essential resources such as food,
mineral ions, refuge from predators, and safe
nesting sites
– In any environment, one essential factor will
run out first, and acts as the brake on
population growth
– Supplying the first limiting factors simply
substitutes one for another – all natural
populations eventually encounter limits
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What Constrains Population Growth?
• Logistic growth
– A pattern of logistic growth shows how a small
population starts growing slowly in size, then
grows rapidly, then levels off as the carrying
capacity is reached
– Plots out as an S-shaped curve
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What Constrains Population Growth?
• Carrying capacity
– Maximum number of individuals of a species
that an environment can sustain
– Ultimately, the sustainable supply of
resources determines population size
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What Constrains Population Growth?
Population size
(number of individuals)
initial carrying capacity
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2
3
4
new carrying capacity
1
What Constrains Population Growth?
• 1944: 29 reindeer introduced to St.
Matthew Island
• 1957: 1,350 well-fed reindeer (lichens)
• 1963: 6,000 hungry reindeer (carry
capacity exceeded)
• 1966: 42 live reindeer, and many bleached
bones
• 1980s: No reindeer
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What Constrains Population Growth?
© Cengage Learning 2015
40.4 How Do Life History Patterns Vary?
• Reproduction-related events that occur
between birth and death make up a life
history pattern
• Life history pattern
– A set of traits related to growth, survival, and
reproduction such as life span, age-specific
mortality, age at first reproduction, and
number of breeding events
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How Do Life History Patterns Vary?
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How Do Life History Patterns Vary?
• Type I survivorship curve
– Elephants have type I survivorship, with low
mortality until old age
– Typical of large animals that bear one or few
offspring at a time and provide extended
parental care
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How Do Life History Patterns Vary?
• Type II survivorship curve
– Snowy egrets are type II population,
with a fairly constant death rate
– Typical of lizards, small mammals, and
large birds
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How Do Life History Patterns Vary?
• Type III survivorship curve
– Sea urchins are type III; mortality is high
for larvae and in old age, but low in
adults
– Typical of species that produce many
small offspring and provide little or no
parental care
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Percentage of survivors (log scale)
100
I
10
II
1
III
0.1
0
50
100
Percentage of maximum life span
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Figure 19.4
How Do Life History Patterns Vary?
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© Cengage Learning 2015
Figure 19.5a
500
Ideal
conditions
20 rabbits to
475 rabbits in
12 months
450
400
Population size (N)
Exponential
growth of a
rabbit
population
350
300
250
200
150
100
50
0
0
1
2
3
4
5
6
7
8
9 10 11 12
Time (months)
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Figure 19.5
Biology and Society:
Multiplying Like Rabbits
– In 1859, 12 pairs of European rabbits were
released on a ranch in southern Australia.
– By 1865, 20,000 rabbits were killed on just that
one ranch.
– By 1900, several hundred million rabbits were
distributed over most of the continent.
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Learning
2015 Inc.
© 2010 Pearson
Education,
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Figure 19.00
– The European rabbits
• Destroyed farming and grazing land
• Promoted soil erosion
• Made grazing treacherous for cattle and sheep
• Competed directly with native marsupials
– The European red fox
• Was introduced to control the rabbits
• Spread across Australia
• Ate several species of native birds and small
mammals to extinction
• Had little impact on the rabbit population
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– In 1950, the Australian government introduced a
virus lethal to European rabbits into the rabbits’
Australian environment.
–Did this work?
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40.6 How Has the Size of the Human
Population Changed Over Time?
• For most of history, the human population
grew very slowly
– In 2009, human population size surpassed 6.8
billion
• Growth rate began to increase about
10,000 years ago, then soared during the
past two centuries
• Three trends promoted the large increases
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How Has the Size of the Human
Population Changed Over Time?
• Three factors of human population growth
– Humans were able to migrate into new
habitats and expand into new climate zones
– Humans developed new technologies that
increased the carrying capacity of existing
habitats
– Humans sidestepped some limiting factors
that restrain growth of other species
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© Cengage Learning 2015
In the developing world
– Death rates have dropped / High birth rates persist
1 Billion : 10,000 Years
2 Billion : 123 Years
3 Billion : 33 Years
4 Billion : 14 Years
5 Billion : 13 Years
6 Billion : 12 Years
7 Billion : 13 Years
8 Billion 12 Years
9 Billion : 24 Years
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How Has the Size of the Human
Population Changed Over Time?
• Human skills that override normal
population limits
– Learned to start fires, build shelters, make
clothing, manufacture tools, and hunts
together
– Language allowed knowledge to pass through
generations
– Agriculture provided a more dependable food
supply
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How Has the Size of the Human
Population Changed Over Time?
• Human skills that override normal
population limits
– Improved sanitation and medical advances
(vaccines, antibiotics) cut the death toll from
disease
– Energy of fossil fuels allowed development of
mechanized agriculture to sustain the ever
larger population
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How Has the Size of the Human
Population Changed Over Time?
• Quality of life is inversely related to
population growth, resource depletion, and
pollution
• Many governments now offer family
planning programs to reduce fertility rates
• Worldwide, total fertility rate has fallen
from 6.5 in 1950 to 2.6 in 2008; and
replacement fertility rate for developed
countries is 2.1
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How Has the Size of the Human
Population Changed Over Time?
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How Has the Size of the Human
Population Changed Over Time?
• Age structure diagrams show the age
distribution of individuals
– The broader the base of an age structure
diagram, the greater proportion of young
people, and the greater expected growth
– More than 1/3 of the world population is in the
broad pre-reproductive base
– World population growth can’t be slowed for
many years, because 1.9 billion people are
about to enter reproductive age
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How Has the Size of the Human Population Changed Over Time?
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How Has the Size of the Human
Population Changed Over Time?
• Future growth
– World population is expected to reach 8.9
billion by 2050, and possibly to decline as the
century ends
– China and India each hold more than one
billion people (together, 38% percent of the
world population); the United States is third,
with 307 million
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40.7 How Does Industrialization Affect
Population Growth?
• The most highly developed countries have
the lowest birth rates and infant mortality,
and the highest life expectancy
• High population growth is correlated with
low levels of economic development, and
low per capita consumption of resources
• Negative population growth in some
countries also poses challenges
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How Does Industrialization Affect
Population Growth?
• On a per capita basis, people in highly
developed countries use far more
resources than those in less developed
countries, and generate more waste and
pollution
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How Does Industrialization Affect
Population Growth?
• Ecological footprint
– Area of Earth’s surface required to sustainably
support a particular level of development and
consumption
– People in China and India consume less than
average
– Per capita footprint of the United States is
more than three times average
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How Does Industrialization Affect
Population Growth? (cont’d.)
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11/25 Friday Schedule
Populations
40
11/27
No Class
12/2
41
12/4
Trophic Levels
12/9
12/16
Ecology
Succession
Biomes & Human 43&44 12/11
Effect
Final Exam
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Lecture Review
Lab Final Exam
42
Vultures evolved an extreme gut to cope with disgusting dietary habits
November 25, 2014
How is it that vultures can live on a diet of carrion that would at least lead to severe food-poisoning,
and more likely kill most other animals?
When vultures eat lunch they happily strip the rotting carcasses they find back to the bone. And if,
however, the animal's hide is too tough to easily pierce with their beak, they don't hesitate to enter it
using other routes, among them the back entrance -- so to speak: via the anus. Although their diet
of meat that is both rotting and liberally contaminated with feces would likely kill most other animals,
they are apparently immune to the cocktail of deadly microbes within their dinner such as Clostridia,
Fuso- and Anthrax-bacteria.
"To investigate vultures' ability to survive eating this putrid cocktail, we generated DNA profiles from
the community of bacteria living on the face and gut of 50 vultures from the USA. Our findings
enable us to reconstruct both the similarities, and differences, between the bacteria found in turkey
vultures and black vultures, distributed widely in the Western Hemisphere. Apparently something
radical happens to the bacteria ingested during passage through their digestive system," says Lars
Hestbjerg Hansen, a professor at Aarhus University who together with PhD-student Michael
Roggenbuck lead the study while he was at the University of Copenhagen.
On average, the facial skin of vultures contained DNA from 528 different types of micro-organisms,
whereas DNA from only 76 types of micro-organisms were found in the gut. Michael Roggenbuck
explains:
"Our results show there has been strong adaptation in vultures when it comes to dealing with the
toxic bacteria they digest. On one hand vultures have developed an extremely tough digestive
system, which simply acts to destroy the majority of the dangerous bacteria they ingest. On the
other hand, vultures also appear to have developed a tolerance towards some of the deadly
bacteria -- species that would kill other animals actively seem to flourish in the vulture lower
intestine."
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How Do Life History Patterns Vary?
• R-selection
– Individuals who produce maximum number
offspring as quickly as possible have a
selective advantage
– Occurs when population density is low and
resources are abundant
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How Do Life History Patterns Vary?
• K-selection
– Individuals who produce offspring that
outcompete others for limited resources have
a selective advantage
– Occurs when a population is near carrying
capacity
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How Does Predation Affect Life History
Traits?
• Overfishing of cod
– In response to fishing pressure on larger fish,
Atlantic codfish began maturing faster and
reproducing younger
– A 1992 ban on cod fishing came too late to
stop the Atlantic cod population from crashing
– Life history changes were early signs of
overfishing – had biologists recognized the
signs, they might have been able to save the
fishery and more than 35,000 jobs
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