Chapter 19- Populations

• A population is a group of organisms of the same species living in the same place at the same time

• Millions of different populations all evolving according to their own self interest in a particular environment.

• But each population is a part of the environment of its neighbors, so any evolutionary change has a ripple effect.

A Population• Group of organisms

of the same species living in the same place at the same time

• Individuals may come and go, but the population can remain the same

Population Growth• Since each organism of a population

is governed by the selfish gene, populations tend to grow

• If unlimited resources are present, growth will be exponential

• It will proceed very quickly for rapidly reproducing organisms and more slowly for slowly reproducing ones

• The curve, however, will always be a “J” curve or an exponential growth curve

Generation # of bacteria time1 1 02 2 15min3 4 30min4 8 45min5 16 1hr6 32 75min7 64 90min8 128 105min9 256 2hrs10 51211 102412 204813 4096 3hrs14 819215 16,38416 32,76817 65,536 4hrs18 131,07219 262,14420 524,28821 1,048,576 5hrs22 2,097,15223 4,194,30424 8,388,608

Population Growth 2• Resources are never unlimited,

though. • As population rises, resources

decline.• If the growth is too rapid,

resources are rapidly depleted and a population crash can occur

• This pattern occurs often with many populations (including humans)

Gypsy moth caterpillar

Population Growth 3• More often what happens is

that the resources slowly decrease, the growth rate slowly decreases, and they meet.

• This point that they oscillate around is the carrying capacity of the environment for that particular organism

• So when would you “harvest” these individuals? (1,2,3,4,or 5)

S - shaped curve

Population Mortality

• Organisms differ on strategies of reproduction and differ on types of predation

• Those organisms that put much care into their few young tend to have good survivorship of young

• Those organisms that spread their young all over tend to have poor survivorship of their young

• A graphic representation of the rates of survival at different ages is called a survivorship curve

Population Density and Dispersion

• Population density is simply the number of individuals measured per unit of area or volume

• Additionally, the population can clump in different ways– Random– Clumped– Regular

Growth Rate Limiting Factors(effecting birth or mortality rates)

Density-Dependent – Predation– Increased competition

for scarce resources– Sickness– Others?...

Density-Independent– Weather

• Ice Age• Global Warming• Flood• El Nino• Etc.

Range of Tolerance is an important factor: temperature, light, salinity, nutrients, water

Human Growth Patterns

What are the causes that allow this to happen?What are some possible consequences of this?What are some possible results of the population boom?What will the future look like?

Graph showing possible future population growth based on Total Fertility Rate - the average number of children a woman has