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Population

A population is a group of organisms that belong to the same species and live in a particular place at the same time; they interbreed with each other

Populations can be measured in terms of

Size

Number of individuals that population can contain

Density

Measure of how crowded the population is

Dispersion

Describes the distribution of individuals within the population and may be random, uniform, or clumped

Clumped; large area and most of the population tends to stay in little groups

Even; spread out evenly

Random: scattered; some of individuals spread out evenly and in other areas there are some grouped

Growth rate

Age Structure

A populations age structure indicates the percentage of individuals at each age

The distribution of individuals among different ages in a population

Survivorship

Patterns of Mortality

Populations show three patterns of mortality or survivorship curves

Type I

Low mortality until late in life

Type II

Constant mortality throughout life

Type III

High mortality early in life followed by low mortality for the remaining life span

Population Growth Rate

Demographers, scientists who study population dynamics, define the growth rate of a population as the amount by which a populations size changes in a given time

Life expectancy

How long, on average, an individual is expected to live

Birth rate

The number of births occurring in a period of time

Death rate or mortality rate

The number of deaths occurring in a period of time

Emigration

The movement of individuals out of a population (out)

Immigration

The number of individuals into a population (in)

Survivorship curve

The graph of a species' mortality rate

Population Size Equations

Birth rate - death rate = growth rate

(Birth rate + immigration) - (death rate + emigration)

End up with zero- stagnant population

Exponential model

A model of population growth that describes a population that increases rapidly after only a few generations

Describes perpetual growth at a steady rate in a population

The model assumes constant birth and death rates and no immigration or emigration.

Exponential growth

Population growth in which the birth and death rates are constant

Growth Factors

Limiting factor

Biotic or abiotic factor that restrains the growth of a population

Carrying capacity

The number of individuals of a species that an ecosystem is capable of supporting

Logistic growth

Population growth in which birth and death rates vary with population size and are equal at the carrying capacity

Logistic model

An expansion of the exponential model that takes into account limiting factors wish as fluctuating birth and death rates

Birth rates fall and death rates climb as the population grows

When the carrying capacity is reached, the number of individuals the environment can support is reached and population growth becomes stable

Population

A population is a group of organisms that belong to the same species and live in a particular place at the same time; they interbreed with each other

Populations can be measured in terms of

Size

Number of individuals that population can contain

Density

Measure of how crowded the population is

Dispersion

Describes the distribution of individuals within the population and may be random, uniform, or clumped

Clumped; large area and most of the population tends to stay in little groups

Even; spread out evenly

Random: scattered; some of individuals spread out evenly and in other areas there are some grouped

Growth rate

Age Structure

A populations age structure indicates the percentage of individuals at each age

The distribution of individuals among different ages in a population

Survivorship

Patterns of Mortality

Populations show three patterns of mortality or survivorship curves

Type I

Low mortality until late in life

Type II

Constant mortality throughout life

Type III

High mortality early in life followed by low mortality for the remaining life span

Population Growth Rate

Demographers, scientists who study population dynamics, define the growth rate of a population as the amount by which a populations size changes in a given time

Life expectancy

How long, on average, an individual is expected to live

Birth rate

The number of births occurring in a period of time

Death rate or mortality rate

The number of deaths occurring in a period of time

Emigration

The movement of individuals out of a population (out)

Immigration

The number of individuals into a population (in)

Survivorship curve

The graph of a species' mortality rate

Population Size Equations

Birth rate - death rate = growth rate

(Birth rate + immigration) - (death rate + emigration)

End up with zero- stagnant population

Exponential model

A model of population growth that describes a population that increases rapidly after only a few generations

Describes perpetual growth at a steady rate in a population

The model assumes constant birth and death rates and no immigration or emigration.

Exponential growth

Population growth in which the birth and death rates are constant

Growth Factors

Limiting factor

Biotic or abiotic factor that restrains the growth of a population

Carrying capacity

The number of individuals of a species that an ecosystem is capable of supporting

Logistic growth

Population growth in which birth and death rates vary with population size and are equal at the carrying capacity

Logistic model

An expansion of the exponential model that takes into account limiting factors wish as fluctuating birth and death rates

Birth rates fall and death rates climb as the population grows

When the carrying capacity is reached, the number of individuals the environment can support is reached and population growth becomes stable