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Unit 5 EcologyUnit 5 Ecology

Ch. 19 PopulationsCh. 19 Populations

Characteristics of Populations

Characteristics of Populations

�3 important characteristics of a population are its size, density, & geographic distribution.

�Population Size—the # of individuals in a population

�3 important characteristics of a population are its size, density, & geographic distribution.

�Population Size—the # of individuals in a population

Characteristics of Populations

Characteristics of Populations

�Population density - the # of individuals per unit area

�Geographic dispersion refers to the area occupied by a population

�Clumped

�Random

�Uniform

�Population density - the # of individuals per unit area

�Geographic dispersion refers to the area occupied by a population

�Clumped

�Random

�Uniform

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ClumpedClumped

UniformUniform

RandomRandom

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Population DynamicsPopulation Dynamics

�Populations are always changing due to:

�Birth rate—

�Death rate—

�Populations are always changing due to:

�Birth rate—

�Death rate—

Survivorship curvesSurvivorship curves

�A survivorship curve is a diagram showing the number of surviving members over time from a measured set of births.

�Help to describe the reproductive strategy of a species.

�A survivorship curve is a diagram showing the number of surviving members over time from a measured set of births.

�Help to describe the reproductive strategy of a species.

�Survivorship curves can be type I, II or III.

�Survivorship curves can be type I, II or III.

– Type I —low level of infant mortality and an older population

– common to large mammals and humans

– Type II —survivorship rate is equal at all stages of life

– common to birdsand reptiles

– Type III —very high birth rate, very high infant mortality

– common to invertebrates and plants

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Population Growth RatePopulation Growth Rate

�Growth rate refers to the speed of a population increasing or decreasing in size

�4 factors affect population size: the birth rate, the death rate (mortality rate), the # of individuals that enter a population (immigration) & the number that leave the population (emigration)

�Growth rate refers to the speed of a population increasing or decreasing in size

�4 factors affect population size: the birth rate, the death rate (mortality rate), the # of individuals that enter a population (immigration) & the number that leave the population (emigration)

Population GrowthPopulation Growth

�Immigration - movement of individuals into an area, can cause a population to grow

�Emigration - movement of individuals out of an area, can cause a population to decrease

�Immigration - movement of individuals into an area, can cause a population to grow

�Emigration - movement of individuals out of an area, can cause a population to decrease

Population GrowthPopulation Growth

�A population can grow when its birth rate is greater than its death rate

�If the birth rate = death rate, the population will stay the same

�If the death rate is greater than the birth rate, the population will decrease

�A population can grow when its birth rate is greater than its death rate

�If the birth rate = death rate, the population will stay the same

�If the death rate is greater than the birth rate, the population will decrease

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Exponential GrowthExponential Growth

�If a population has plenty of space & food, & is protected from predators & disease, then organisms in that population will multiply & it will increase in size

�Exponential growth - occurs when the individuals in a population reproduce at a constant rate

�If a population has plenty of space & food, & is protected from predators & disease, then organisms in that population will multiply & it will increase in size

�Exponential growth - occurs when the individuals in a population reproduce at a constant rate

Exponential GrowthExponential Growth

�Model in which pop. grows without limit at its maximum rate.

�This rate = biotic potential and symbol is r.

�r = (b-d) + (i-e)

�b = birth rate i = immigration (coming)

�d = death rate e = emigration

(leaving)

�Sometimes a population can be increased more by immigration than the birth rate.

�Model in which pop. grows without limit at its maximum rate.

�This rate = biotic potential and symbol is r.

�r = (b-d) + (i-e)

�b = birth rate i = immigration (coming)

�d = death rate e = emigration

(leaving)

�Sometimes a population can be increased more by immigration than the birth rate.

Exponential Cont.Exponential Cont.

�Exponential growth usually only occurs for a short period of time.�ex. algae colonizing a new pond

�organisms in a new habitat

�Eventually all populations will reach the carrying capacity (the number of individuals a place can support)�symbolized by k

�J-shaped curve

�Exponential growth usually only occurs for a short period of time.�ex. algae colonizing a new pond

�organisms in a new habitat

�Eventually all populations will reach the carrying capacity (the number of individuals a place can support)�symbolized by k

�J-shaped curve

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Logistic GrowthLogistic Growth

�Occurs when a population’s growth stops or slows down

�S-curve

�Usually occurs after a period of exponential growth.

�Occurs when a population’s growth stops or slows down

�S-curve

�Usually occurs after a period of exponential growth.

Logistic GrowthLogistic Growth

�Carrying capacity - the # of individuals in a population, that an environment can support

�Shown in a graph, when a population levels off

�Carrying capacity - the # of individuals in a population, that an environment can support

�Shown in a graph, when a population levels off

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Logistic GrowthLogistic Growth

�Model in which population grows and growth rate slows as it reaches carrying capacity.

�As N approaches K, the rate of pop. growth slows. (N= # of individuals present at any one time)

�Factors that create this are:

�increasing competition for limited resources

�buildup of waste

�increased predation

�S-shaped curve

�Model in which population grows and growth rate slows as it reaches carrying capacity.

�As N approaches K, the rate of pop. growth slows. (N= # of individuals present at any one time)

�Factors that create this are:

�increasing competition for limited resources

�buildup of waste

�increased predation

�S-shaped curve

Population Growth Cont.Population Growth Cont.

Phases of population growth:

1. Lag phase- a period of very slow growth in a population

2. Exponential phase- a period of rapid growth in a population

3. Stabilization phase- a period when no growth in a population occurs because it has reached carrying capacity.

Phases of population growth:

1. Lag phase- a period of very slow growth in a population

2. Exponential phase- a period of rapid growth in a population

3. Stabilization phase- a period when no growth in a population occurs because it has reached carrying capacity.

Applying Growth ModelsApplying Growth Models

�r - selected adaptation:�adaptations favor a high rate of increase, no limits as of yet.�ex.. dandelion, aphids, mice, cockroaches

�k - selected adaptations:�all favor reproduction near the carrying capacity of the species.�ex.. whooping cranes, whales, coconut palm

�What is the difference in offspring and rate of reproduction between the r & k selected species?

�r - selected adaptation:�adaptations favor a high rate of increase, no limits as of yet.�ex.. dandelion, aphids, mice, cockroaches

�k - selected adaptations:�all favor reproduction near the carrying capacity of the species.�ex.. whooping cranes, whales, coconut palm

�What is the difference in offspring and rate of reproduction between the r & k selected species?

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Limits to GrowthLimits to Growth

�Limiting factor - a factor that causes population growth to decrease

�Limiting factor - a factor that causes population growth to decrease

Limits to GrowthLimits to Growth

�Density-dependent factor - a limiting factor that depends on population size

�EXAMPLES:�Competition

�Predation

�Parasitism

�Disease

�Density-dependent factor - a limiting factor that depends on population size

�EXAMPLES:�Competition

�Predation

�Parasitism

�Disease

Limits to GrowthLimits to Growth

�Competition:

�When populations become crowded, organisms compete with each other for food, water, space, sunlight, etc.

�Competition will cause 2 different species to evolve over time, to occupy separate niches, therefore, less competition

�Competition:

�When populations become crowded, organisms compete with each other for food, water, space, sunlight, etc.

�Competition will cause 2 different species to evolve over time, to occupy separate niches, therefore, less competition

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Limits to GrowthLimits to Growth�Predation:

�The regulation of a population by predation takes place within a predator-prey relationship

�Predation:

�The regulation of a population by predation takes place within a predator-prey relationship

Limits to GrowthLimits to Growth

�Parasitism & Disease:

�Parasites can limit the growth of a population, by acting as predators

�Many take the nourishment of their hosts, some cause disease & even death

�Parasitism & Disease:

�Parasites can limit the growth of a population, by acting as predators

�Many take the nourishment of their hosts, some cause disease & even death

Limits to GrowthLimits to Growth

�Density-independent factors -affect all populations in similar ways, regardless of population size

�Examples include: unusual weather, natural disasters, seasonal changes, & certain human activities (damming rivers, clear-cutting forests)

�Density-independent factors -affect all populations in similar ways, regardless of population size

�Examples include: unusual weather, natural disasters, seasonal changes, & certain human activities (damming rivers, clear-cutting forests)

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Influence of Population

DensityDensity-Dependent Effects- only become limiting factors

when the population density (# of organisms in a certain area) reaches a certain level.

3 density-dependent factors:

1.Competition - when populations are crowded, there is a

struggle for food

2.Predation - controls a population size

predator-prey relationship- most well-known population

control

Ex.. wolves and moose, as moose population fall, soon after

wolf population fall, etc..

3.Parasitism and Disease - take nourishment from the host and

weaken it or kill it.

Influence of Population

Density� Density-Independent Effects- affect all populations in a

similar way regardless of population size.

Some types of density-independent factors are:

1. Unusual weather

2. Natural disaster

3. Seasonal cycles

4. Certain human activities- damage to rivers or

lakes, clear cut forests

Limits to GrowthLimits to Growth

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Human Population GrowthHuman Population Growth

�In the US & other developed countries, the current growth rate is very low

�In some developing countries, the population growth rate is nearly 3 people per second

�Because of this, the human population is on its way to reaching 9 billion people within your lifetime

�In the US & other developed countries, the current growth rate is very low

�In some developing countries, the population growth rate is nearly 3 people per second

�Because of this, the human population is on its way to reaching 9 billion people within your lifetime

Historical OverviewHistorical Overview

�Like the populations of many other living organisms, the size of the human population tends to increase with time

�Like the populations of many other living organisms, the size of the human population tends to increase with time

Patterns of Population Growth

Patterns of Population Growth

�The human population cannot keep growing exponentially forever, because Earth & its resources are limited

�Experts have predicted that war, famine, & disease would limit human population growth

�The human population cannot keep growing exponentially forever, because Earth & its resources are limited

�Experts have predicted that war, famine, & disease would limit human population growth

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Population DemographyPopulation Demography

�Demography- the statistical study of populations to make predictions.

�Age structure:�cohort- group of individuals the same age.

�fecundity- characteristic birth rate of a cohort

�mortality- characteristic death rate of a cohort

�A population’s growth depends directly on fecundity and mortality.

�Demography- the statistical study of populations to make predictions.

�Age structure:�cohort- group of individuals the same age.

�fecundity- characteristic birth rate of a cohort

�mortality- characteristic death rate of a cohort

�A population’s growth depends directly on fecundity and mortality.

Patterns of Population Growth

Patterns of Population Growth

�Population growth depends on how many people of different ages make up a given population

�Age-structure diagrams -population profiles that demographers can use to predict future growth

�Population growth depends on how many people of different ages make up a given population

�Age-structure diagrams -population profiles that demographers can use to predict future growth

Patterns of Population Growth

Patterns of Population Growth

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An Uncertain FutureAn Uncertain Future

� The rapidly growing human population is the biosphere’s greatest challenge!

�250 new babies a day

�1 million people every 3 days

�Of the new billion people in the 1990’s, 90% will live in developing countries.

� 85% of the worlds wealth in developed countries & 15% in developing countries

� 23% of the world’s pop. lives in developed countries while 77% live in developing countries.

� The rapidly growing human population is the biosphere’s greatest challenge!

�250 new babies a day

�1 million people every 3 days

�Of the new billion people in the 1990’s, 90% will live in developing countries.

� 85% of the worlds wealth in developed countries & 15% in developing countries

� 23% of the world’s pop. lives in developed countries while 77% live in developing countries.

Future Population GrowthFuture Population Growth

�Demographers predict that the human population will be growing more slowly over the next 50 years

�Demographers predict that the human population will be growing more slowly over the next 50 years