how populations change

HOW POPULATIONS CHANGEChapter 8 Section 1

A POPULATION IS…all the members of a species living

in the same place at the same time

3 PROPERTIES OF POPULATIONS…

SIZE – number of individuals in the population How many?DENSITY – number of individuals per area or volume

How tightly packed? DISPERSION – the distribution or arrangement of

a population within a given space can be dispersed evenly (uniformly), clumped,

random

WHAT FACTORS AFFECT THE SIZE OF A POPULATION? Births, Deaths, Immigration and Emigration

Immigration - when individuals move into a population

Emigration- when individuals leave a population

EMIGRATION AFTER THE CIVIL WAR

Confederate Colonies of Brazil: The Confederados

o at the end of the Civil War (1860's) some Confederates left the US (emigrated) to South

America o numbered in the thousandso settled primarily in Brazil – coastal areaso some returned to their homes in the United States,

but many more settled permanently in Brazil and their

descendants are living there today

HOW DOES A POPULATION CHANGE?

Populations grow when… there are more births than deaths or when individuals move into the population.

Populations decline when… there are more deaths than births or when individuals leave the population .

POPULATION GROWTH IS…a change in the size of a population over time

GROWTH RATE = birth rate – death rate

Growth rates can be… positive, negative or zero positive growth – more births than deaths negative growth – fewer births than deaths zero growth – number of births = number of

deaths

GROWTH RATE

REPRODUCTIVE POTENTIALThe maximum number of offspring that

each member of a population can produce Some species have higher reproductive

potentials than others Insects have a large reproductive potential as

compared to humans

REPRODUCTIVE STRATEGIES

“R” strategists – overcome massive loss of offspring by producing many offspring – in hopes that some will survive

Example – insects

“K” strategists – have fewer offspring and longer generation times

Example - humans

R STRATEGIST (MANY OFFSPRING) OR K STRATEGIST (FEW OFFSPRING)

2 Types of population growth models …

exponential growth and logistic growth

Time

EXPONENTIAL GROWTH

Populations sometimes undergo exponential growth which means that the population grows faster and faster

“J” shaped graph

Exponential growth occurs in nature only when there is plenty of food and space and little or no competition or predators

EXPONENTIAL GROWTH OF HUMAN POPULATION

LOGISTICAL GROWTH

Populations sometimes undergo logistical growth which means the growth rate decreases with increasing number of individuals until it becomes zero when the population reaches a maximum

“S” shaped graph

LOGISTICAL GROWTH

LINEAR GROWTH means a population grows by a fixed amount each

generation a steady increase in a population this type of growth is not characteristics of most

populations

WHAT LIMITS THE GROWTH OF A POPULATION?

Carrying Capacity – the maximum population size that an environment (or ecosystem) can sustain

Populations cannot grow indefinitely A population may increase beyond its carrying

capacity but this cannot be maintained Because ecosystems change, the carrying capacity

is difficult to predict or calculate exactly

WHAT ELSE LIMITS A POPULATION?

RESOURCES - water, sunlight, minerals,… The most severely limited resources will

determine the carrying capacity of an environment!

COMPETITION - for food, shelter (habitat) and mates

PREDATORS

2 TYPES OF LIMITING FACTORS IN ECOSYSTEMS

Density Dependent

Factors

Resources that decrease as a

population increases

Density Independent Factors

Environmental factors that affect

all populations equally

Density Dependent Factor(s) – Resources that decrease as a population

increases regulate a population when individuals

are densely packed (crowded) together

Examples – limited resources, predation, disease,

food, water, shelter, space,….

Density Independent Factor(s) – Environmental factors that affect all

populations equally regulate a population regardless of the

population’s density – this type of regulation affects all members of a population Examples – severe weather, current,

natural disasters, climate, temperature, precipitation, salinity,…