Ch 5- Population• Why do populations change?• There are 3 important

characteristics of a population- Geographic distribution, density and growth rate

• Geographic distribution- the area inhabited by a population

• Population density- number of individuals per unit area– Depends on species and its

ecosystem

Population Growth

• What factors affect population size?– # of births, # of deaths, and # of individuals that enter

and leave the population• Immigration- the movement of individuals into an

area• Emigration- the movement of individuals out of an

area• What causes these movements?– Young animals reach maturity search for mates,

shortage of food

Exponential Growth

• Individuals in a population reproduce at a constant rate

• Under ideal conditions with unlimited resources, and in the absence of predation and disease, a population will grow exponentially

Logistic Growth

• A population’s growth slows or stops following a period of exponential growth

• Why might this happen?– Resources become less available

• Carrying capacity- the largest number of individuals that a given environment can support

• Many natural populations follow the logistic growth curve

Sec 2- Limits to Growth

• Limiting factors- factor that causes population growth to decrease

• A resource can also affect long term survival of a species– Pandas

• Density-dependent factors- limiting factor that depends on population size– Factors greatly affect large and dense populations– Factors include; competition, predation, parasitism,

and disease

• Competition may occur between individuals of same species or of different species– The more individuals the faster the resources are

used up– Competition between different species leads to

evolutionary change• Predation- often controls populations in nature– Moose populations rise, wolves population soon

rises. Moose populations soon decrease, later followed by the decline in wolves

• Parasitism and disease- range in size, similar to predators, take nourishment from host, weakening or causing death to them

• Density-Independent Factors- affect all populations in similar ways, regardless of population size– Unusual weather– Natural disasters– Seasonal cycles– Certain human activities- clearing forests,

damming rivers• Environments are always changing, most

populations can adapt to certain amount of change

Sec 3- Human Population Growth

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

• Think back to early human existence, how has human populations increase?

• Can the human population keep growing exponentially forever?

• Are birthrates, death-rates, and age structure the same in every country?

• Demography- scientific study of human populations• Demographic transition- dramatic change in birth and

death rates– Change from high birthrates and high death rates to low

birthrates and low death rates• What causes changes?

– Birth rates exceed death rates, advances in nutrition, sanitation, and medicine. Population increases rapidly. Societies modernize, people have less kids, population growth slows

• Age Structure diagrams- shows the population of a country by gender and age– Can predict future growth

• Future Population growth- world population will continue to rise but at a slower rate