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Population Growth APBio

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Information about Population Growth APBio

Published on February 28, 2008

Author: MrDPMWest

Source: slideshare.net

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Population Growth and Regulation

The Study of Ecology Ecology : the study of interrelationships between living things and their nonliving environment The environment consists of two components Abiotic component: nonliving, such as soil and weather Biotic component: all living forms of life

Ecology : the study of interrelationships between living things and their nonliving environment

The environment consists of two components

Abiotic component: nonliving, such as soil and weather

Biotic component: all living forms of life

The Study of Ecology Ecology can be studied at several organizational levels Populations : all members of a single species living in a given time and place and actually or potentially interbreeding Ecosystem : all the interacting populations in a given time and place Communities : all the organisms and their nonliving environment in a defined area Biosphere : all life on Earth

Ecology can be studied at several organizational levels

Populations : all members of a single species living in a given time and place and actually or potentially interbreeding

Ecosystem : all the interacting populations in a given time and place

Communities : all the organisms and their nonliving environment in a defined area

Biosphere : all life on Earth

How Does Population Size Change? Several processes can change the size of populations Birth and immigration add individuals to a population Death and emigration remove individuals from the population Change in population size = (births – deaths) + (immigrants – emigrants)

Several processes can change the size of populations

Birth and immigration add individuals to a population

Death and emigration remove individuals from the population

Change in population size

= (births – deaths) + (immigrants – emigrants)

How Does Population Size Change? Ignoring migration, population size is determined by two opposing forces Biotic potential : the maximum rate at which a population could increase when birth rate is maximal and death rate minimal Environmental resistance : limits set by the living and nonliving environment that decrease birth rates and/or increase death rates (examples: food, space, and predation)

Ignoring migration, population size is determined by two opposing forces

Biotic potential : the maximum rate at which a population could increase when birth rate is maximal and death rate minimal

Environmental resistance : limits set by the living and nonliving environment that decrease birth rates and/or increase death rates (examples: food, space, and predation)

Population Growth The growth rate ( r ) of a population is the change in the population size per individual over some time interval Determined by Growth rate ( r ) = birth rate ( b ) – death rate ( d )

The growth rate ( r ) of a population is the change in the population size per individual over some time interval

Determined by

Growth rate ( r ) = birth rate ( b ) – death rate ( d )

Population Growth Birth rate ( b ) is the average number of births per individual per unit time Example: if there are 5 births among 10 individuals, b = 5/10 = 0.5

Birth rate ( b ) is the average number of births per individual per unit time

Example: if there are 5 births among 10 individuals, b = 5/10 = 0.5

Population Growth Death rate ( d ) is the proportion of individuals dying per unit time Example: if 4 of 10 individuals die, d = 4/10 = 0.4 Thus, r = b – d = 0.5 – 0.4 = 0.1

Death rate ( d ) is the proportion of individuals dying per unit time

Example: if 4 of 10 individuals die, d = 4/10 = 0.4

Thus, r = b – d

= 0.5 – 0.4

= 0.1

Population Growth Population growth per unit of time can be calculated by multiplying growth rate ( r ) by the original population size ( N ) Population growth (G) = rN In the previous example, population growth = rN = 0.1(10) = 1 , so the population has grown by one individual

Population growth per unit of time can be calculated by multiplying growth rate ( r ) by the original population size ( N )

Population growth (G) = rN

In the previous example, population growth = rN = 0.1(10) = 1 , so the population has grown by one individual

Population Growth To determine the size of the population at the end of the time period, add the population growth ( rN ) to the initial population size ( N ) = N + rN = 10 + 0.1(10) = 10 + 1 = 11

To determine the size of the population at the end of the time period, add the population growth ( rN ) to the initial population size ( N )

= N + rN

= 10 + 0.1(10)

= 10 + 1

= 11

Exponential Growth Exponential growth occurs when a population continuously grows at a fixed percentage of its size at the beginning of each time period This results in a J-shaped growth curve

Exponential growth occurs when a population continuously grows at a fixed percentage of its size at the beginning of each time period

This results in a J-shaped growth curve

Exponential Growth Doubling time describes the amount of time it takes to double its population at its current state of growth Doubling time can be calculated as 0.7 divided by r In our previous example, 0.7/0.1 = 7 time intervals

Doubling time describes the amount of time it takes to double its population at its current state of growth

Doubling time can be calculated as 0.7 divided by r

In our previous example, 0.7/0.1 = 7 time intervals

Biotic Potential Biotic potential is influenced by several factors The age at which the organism first reproduces Populations that have their offspring earlier in life tend to grow at a faster rate (2) The frequency at which reproduction occurs

Biotic potential is influenced by several factors

The age at which the organism first reproduces

Populations that have their offspring earlier in life tend to grow at a faster rate

(2) The frequency at which reproduction occurs

Exponential Growth Curves

Exponential Growth Curves

Biotic Potential (3) The average number of offspring produced each time (4) The length of the organism's reproductive life span (5) The death rate of individuals Increased death rates can slow the rate of population growth significantly

(3) The average number of offspring produced each time

(4) The length of the organism's reproductive life span

(5) The death rate of individuals

Increased death rates can slow the rate of population growth significantly

Effect of Death Rates on Population Growth No deaths 10% die between doublings 25% die between doublings bacteria

Exponential Growth Exponential growth cannot continue indefinitely All populations that exhibit exponential growth must eventually stabilize or crash Exponential growth can be observed in populations that undergo boom-and-bust cycles Periods of rapid growth followed by a sudden massive die-off

Exponential growth cannot continue indefinitely

All populations that exhibit exponential growth must eventually stabilize or crash

Exponential growth can be observed in populations that undergo boom-and-bust cycles

Periods of rapid growth followed by a sudden massive die-off

Exponential Growth Boom-and-bust cycles can be seen in short lived, rapidly reproducing species Ideal conditions encourage rapid growth Deteriorating conditions encourage massive die-off Example Each year cyanobacteria in a lake may exhibit exponential growth when conditions are ideal, but crash when they have depleted their nutrient supply

Boom-and-bust cycles can be seen in short lived, rapidly reproducing species

Ideal conditions encourage rapid growth

Deteriorating conditions encourage massive die-off

Example

Each year cyanobacteria in a lake may exhibit exponential growth when conditions are ideal, but crash when they have depleted their nutrient supply

A Boom-and-bust Population Cycle Conditions good, Boom; Conditions bad, Bust

Conditions good, Boom; Conditions bad, Bust

Exponential Growth Example Lemming cycles are more complex and involve overgrazing of food supply, large migrations, and massive mortality caused by predators and starvation

Example

Lemming cycles are more complex and involve overgrazing of food supply, large migrations, and massive mortality caused by predators and starvation

Lemming Population Cycles

Environmental Resistance Limits Population Growth Decreases birthrate, increases death rate Density-dependent factors Predation Parasitism Competition (inter- and intraspecific) Density-independent factors Weather, pesticides, pollutants Causes populations to stabilize at or below carrying capacity Maximum population size an area can support long term Limitations on population growth necessary

Decreases birthrate, increases death rate

Density-dependent factors

Predation

Parasitism

Competition (inter- and intraspecific)

Density-independent factors

Weather, pesticides, pollutants

Causes populations to stabilize at or below carrying capacity

Maximum population size an area can support long term

Limitations on population growth necessary

The S-Curve of Population Growth (biotic potential) Carrying Capacity Exponential Growth Equilibrium (environmental resistance) Number of Individuals Time

Environmental Resistance Carrying capacity ( K ) is the maximum population size that can be sustained by an ecosystem for an extended time without damage to the ecosystem

Carrying capacity ( K ) is the maximum population size that can be sustained by an ecosystem for an extended time without damage to the ecosystem

 

 

Environmental Resistance Logistic population growth can occur in nature when a species moves into a new habitat, e.g. barnacles colonizing bare rock along a rocky ocean shoreline Initially, new settlers may find ideal conditions that allow their population to grow almost exponentially As population density increases, individuals compete for space, energy, and nutrients

Logistic population growth can occur in nature when a species moves into a new habitat, e.g. barnacles colonizing bare rock along a rocky ocean shoreline

Initially, new settlers may find ideal conditions that allow their population to grow almost exponentially

As population density increases, individuals compete for space, energy, and nutrients

The Effects of Exceeding Carrying Capacity

Environmental Resistance Environmental resistance can be classified into two broad categories Density-independent factors Density-dependent factors

Environmental resistance can be classified into two broad categories

Density-independent factors

Density-dependent factors

Density-Independent Factors Density-independent factors limit populations regardless of their density Examples: climate, weather, floods, fires, pesticide use, pollutant release, and overhunting Some species have evolved means of limiting their losses Examples: seasonally migrating to a better climate or entering a period of dormancy when conditions deteriorate

Density-independent factors limit populations regardless of their density

Examples: climate, weather, floods, fires, pesticide use, pollutant release, and overhunting

Some species have evolved means of limiting their losses

Examples: seasonally migrating to a better climate or entering a period of dormancy when conditions deteriorate

Density-Dependent Factors Density-dependent factors become more effective as population density increases Exert negative feedback effect on population size Density-dependent factors can cause birth rates to drop and/or death rates to increase Population growth slows resulting in an S-shaped growth curve (or S-curve )

Density-dependent factors become more effective as population density increases

Exert negative feedback effect on population size

Density-dependent factors can cause birth rates to drop and/or death rates to increase

Population growth slows resulting in an S-shaped growth curve (or S-curve )

Density-Dependent Factors At carrying capacity, each individual's share of resources is just enough to allow it to replace itself in the next generation At carrying capacity birth rate ( b ) = death rate ( d )

At carrying capacity, each individual's share of resources is just enough to allow it to replace itself in the next generation

At carrying capacity birth rate ( b ) = death rate ( d )

Density-Dependent Factors Carrying capacity is determined by the continuous availability of resources Include community interactions Predation Parasitism Competition

Carrying capacity is determined by the continuous availability of resources

Include community interactions

Predation

Parasitism

Competition

Predation Predation involves a predator killing a prey organism in order to eat it Example: a pack of grey wolves hunting an elk Predators exert density-dependent controls on a population Increased prey availability can increase birth rates and/or decrease death rates of predators Prey population losses will increase

Predation involves a predator killing a prey organism in order to eat it

Example: a pack of grey wolves hunting an elk

Predators exert density-dependent controls on a population

Increased prey availability can increase birth rates and/or decrease death rates of predators

Prey population losses will increase

Predation There is often a lag between prey availability and changes in predator numbers Overshoots in predator numbers may cause predator-prey population cycles Predator and prey population numbers alternate cycles of growth and decline Predation may maintain prey populations near carrying capacity “ Surplus" animals are weakened or more exposed

There is often a lag between prey availability and changes in predator numbers

Overshoots in predator numbers may cause predator-prey population cycles

Predator and prey population numbers alternate cycles of growth and decline

Predation may maintain prey populations near carrying capacity

“ Surplus" animals are weakened or more exposed

Population Cycles in Predators and Prey

Experimental Predator– prey Cycles

Parasitism Parasitism involves a parasite living on or in a host organism, feeding on it but not generally killing it Examples: bacterium causing Lyme disease, some fungi, intestinal worms, ticks, and some protists While parasites seldom directly kill their hosts, they may weaken them enough that death due to other causes is more likely Parasites spread more readily in large populations

Parasitism involves a parasite living on or in a host organism, feeding on it but not generally killing it

Examples: bacterium causing Lyme disease, some fungi, intestinal worms, ticks, and some protists

While parasites seldom directly kill their hosts, they may weaken them enough that death due to other causes is more likely

Parasites spread more readily in large populations

Spatial Distributions The spatial pattern in which individuals are dispersed within a given area is that population’s distribution, which may vary with time There are three major types of spatial distributions Clumped Uniform Random

The spatial pattern in which individuals are dispersed within a given area is that population’s distribution, which may vary with time

There are three major types of spatial distributions

Clumped

Uniform

Random

Spatial Distributions Clumped distribution – includes family and social groups Examples: elephant herds, wolf packs, prides of lions, flocks of birds, and schools of fish Advantages Provides many eyes that can search for localized food sources Confuses predators with sheer numbers Cooperation for hunting more effectively

Clumped distribution – includes family and social groups

Examples: elephant herds, wolf packs, prides of lions, flocks of birds, and schools of fish

Advantages

Provides many eyes that can search for localized food sources

Confuses predators with sheer numbers

Cooperation for hunting more effectively

Population Distributions: Clumped

Spatial Distributions Uniform distribution – constant distance maintained between individuals; common among territorial animals defending scarce resources or defending breeding territories Examples: iguanas, shorebirds, tawny owls Advantage: a uniform distribution helps ensure adequate resources for each individual

Uniform distribution – constant distance maintained between individuals; common among territorial animals defending scarce resources or defending breeding territories

Examples: iguanas, shorebirds, tawny owls

Advantage: a uniform distribution helps ensure adequate resources for each individual

Population Distributions: Uniform

Spacial Distributions Random distribution – rare, exhibited by individuals that do not form social groups; occurs when resources are not scarce enough to require territorial spacing Examples: Trees and other plants in rain forests

Random distribution – rare, exhibited by individuals that do not form social groups; occurs when resources are not scarce enough to require territorial spacing

Examples: Trees and other plants in rain forests

Population Distributions: Random

Survivorship in Populations Survivorship describes the pattern of survival in a population Life tables track groups of organisms born at the same time throughout their life span, recording how many continue to survive in each succeeding year

Survivorship describes the pattern of survival in a population

Life tables track groups of organisms born at the same time throughout their life span, recording how many continue to survive in each succeeding year

 

Survivorship in Populations A survivorship curve for a population can be produced by graphing life table survivorship data Y-axis: the log of the number of individuals surviving to a particular age X-axis: age Three types of survivorship curves can be distinguished Late loss Constant loss Early loss

A survivorship curve for a population can be produced by graphing life table survivorship data

Y-axis: the log of the number of individuals surviving to a particular age

X-axis: age

Three types of survivorship curves can be distinguished

Late loss

Constant loss

Early loss

Survivorship Curves

Survivorship in Populations "Late loss" curves : seen in many animals with few offspring that receive substantial parental care; are convex in shape, with low mortality until individuals reach old age Examples: humans and many large mammals

"Late loss" curves : seen in many animals with few offspring that receive substantial parental care; are convex in shape, with low mortality until individuals reach old age

Examples: humans and many large mammals

Survivorship in Populations "Constant loss" curves : an approximate straight line, indicates an equal chance of dying at any age Example: some bird species

"Constant loss" curves : an approximate straight line, indicates an equal chance of dying at any age

Example: some bird species

Survivorship in Populations "Early loss" curves : high early mortality as most offspring fail to become established; are concave in shape Typical of most plants and many animals that do not receive parental care Examples: most invertebrates and fish

"Early loss" curves : high early mortality as most offspring fail to become established; are concave in shape

Typical of most plants and many animals that do not receive parental care

Examples: most invertebrates and fish

Human Population Growing exponentially Exponential growth will continue (age-structure) Developed countries with more stable populations We continue to overcome environmental resistance Medical advances, agricultural revolution U.S. population Growing faster than world average (>1% annually) Immigration accounts for 30% of our growth Baby boomers are at reproductive age

Growing exponentially

Exponential growth will continue (age-structure)

Developed countries with more stable populations

We continue to overcome environmental resistance

Medical advances, agricultural revolution

U.S. population

Growing faster than world average (>1% annually)

Immigration accounts for 30% of our growth

Baby boomers are at reproductive age

Rapid Human Population Growth In the last few centuries, the human population has grown at nearly an exponential rate Follows a J-shaped growth curve

In the last few centuries, the human population has grown at nearly an exponential rate

Follows a J-shaped growth curve

Technological Advances Most species must "make due" with the resources in an area Humans have manipulated the environment to increase the Earth’s carrying capacity Several technological “revolutions” have greatly influenced the human ability to make resources available Technical and cultural revolution Agricultural revolution Industrial-medical revolution

Most species must "make due" with the resources in an area

Humans have manipulated the environment to increase the Earth’s carrying capacity

Several technological “revolutions” have greatly influenced the human ability to make resources available

Technical and cultural revolution

Agricultural revolution

Industrial-medical revolution

Human Population Growth

Demographic Transition In "developed" countries, the industrial-medical revolution resulted in an initial rise in population, which then stabilized Caused by a decrease in death rates, followed later by a decrease in birth rates

In "developed" countries, the industrial-medical revolution resulted in an initial rise in population, which then stabilized

Caused by a decrease in death rates, followed later by a decrease in birth rates

Pop. Growth Rates: Developed & Developing Countries Developing Countries Developed Countries

Demographic Transition Declining birth rates associated with demographic transition result from many factors Better education Increased access to contraceptives Shift of populations to cities (children provide fewer advantages than in agricultural areas) More women working outside the home

Declining birth rates associated with demographic transition result from many factors

Better education

Increased access to contraceptives

Shift of populations to cities (children provide fewer advantages than in agricultural areas)

More women working outside the home

Demographic Transition Demographic transition has occurred in most developed countries When the adults of a population have just enough children to replace themselves, the situation is called replacement-level fertility (RLF) Because not all children survive to maturity, RLF is slightly higher than 2

Demographic transition has occurred in most developed countries

When the adults of a population have just enough children to replace themselves, the situation is called replacement-level fertility (RLF)

Because not all children survive to maturity, RLF is slightly higher than 2

Uneven Distribution Many "developing" countries still have rapidly growing populations, as birth rates vastly exceed death rates As in developed countries, death rates from infectious disease and starvation are low However, birth rates remain high Low incomes and the need for many children to raise family income or produce food Knowledge of and access to contraception are limited

Many "developing" countries still have rapidly growing populations, as birth rates vastly exceed death rates

As in developed countries, death rates from infectious disease and starvation are low

However, birth rates remain high

Low incomes and the need for many children to raise family income or produce food

Knowledge of and access to contraception are limited

Population Age Structure Age structure Refers to the distribution of human populations according to age groups Age structure can be shown graphically Age is shown on the vertical axis The number of individuals in each age group is shown on the horizontal axis, with males and females placed on opposite sides

Age structure

Refers to the distribution of human populations according to age groups

Age structure can be shown graphically

Age is shown on the vertical axis

The number of individuals in each age group is shown on the horizontal axis, with males and females placed on opposite sides

Population Age Structure All age-structure diagrams peak at the maximum life span, but the shape below the peak reveals if the population is expanding, stable, or shrinking

All age-structure diagrams peak at the maximum life span, but the shape below the peak reveals if the population is expanding, stable, or shrinking

Generalized Age-Structure Diagrams Post-Reproductive (46-100 y old) Reproductive (15-45 y old) Pre-Reproductive (0-14 y old) Expanding Stable Contracting

Age Structures Compared

Age Structures Compared

Population Age Structure These diagrams reveal that even if developing countries were to achieve RLF immediately, their population increases would continue for decades A large population of children today create a momentum for future growth as they enter their reproductive years

These diagrams reveal that even if developing countries were to achieve RLF immediately, their population increases would continue for decades

A large population of children today create a momentum for future growth as they enter their reproductive years

Fertility in Europe A comparison of growth rates for various world regions shows Europe as the only one with average rate of change that is negative

A comparison of growth rates for various world regions shows Europe as the only one with average rate of change that is negative

Population Growth by World Regions 0 0.5 1 1.5 2 2.5 3 -0.5 World Average 1.4% Developing Countries 1.7% Africa 2.4% Latin America/Caribbean 1.8% Asia (excluding China) 1.7% China 0.9% North America 0.6% Developed Countries 0.1% Europe -0.1% Natural Increase (annual %)

The U.S. Population U.S. population is fastest growing of all industrial nations U.S. fertility rate is only ~2.0, actually below RLF However, immigration is adding people rapidly

U.S. population is fastest growing of all industrial nations

U.S. fertility rate is only ~2.0, actually below RLF

However, immigration is adding people rapidly

U.S. Population Growth U. S. over-consumes and over-pollutes U.S. citizen uses 6X energy of average world citizen 4.7% of world population 22% of carbon dioxide and CFC emissions

U. S. over-consumes and over-pollutes

U.S. citizen uses 6X energy of average world citizen

4.7% of world population

22% of carbon dioxide and CFC emissions

The End

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