Population Distribution 1.

1.Population Distribution→ How individual organisms are spread out in their habitats

Population Distribution

How individual organisms are spread out in their environments

▪ Clumped (clustered, grouped)▪ Random (no visible pattern)▪ Uniform (neat, organized, evenly spaced)

Tigers

Tigers are mostly solitary, apart from associations between mother and offspring. Individual tigers have a large territory, and the territories rarely overlap.

Distribution: uniform/randomDensity: lowReason: territorial, solitary animals

Bison

Female bison live in maternal herds which include other females and their offspring. When males become adults, they leave their maternal herd and join other males in bachelor herds. Herds do not typically mingle until mating season.

Distribution: clumpedDensity: highReason: herding animals

Ants

Ants form colonies that range in size from a few dozen individuals to highly organised colonies that may occupy large territories and consist of millions of individuals.

Distribution: clumpedDensity: highReason: colonial animals

Dandelions

Dandelions depend on wind to spread their seeds. Most people consider dandelions to be a weed, but others actually harvest them to eat and turn into tea!

Distribution: randomDensity: highReason: seed dispersal based on wind

Apple Trees in an Orchard

Distribution: uniformDensity: highReason: planted in rows

What Factors Affect Population Density?

1. Density-Dependent Factors→ increase as population increases

▫ Food supply▫ Parasites▫ Disease▫ Competition▫ Predation

2. Density-Independent Factors→ are not affected by population increase or decrease

▫ Rainfall▫ Flood▫ Acidity▫ Drought

2.Population Growth→ How populations increase in size

How can populations change size?

BirthsDeathsImmigration (organisms moving IN)Emigration (organisms moving OUT)

Growing populationB + I > D + E

Constant populationB + I = D + E

Shrinking populationB + I < D + E

Exponential Growth

Happens under:▪ Ideal conditions▪ Unlimited resources

The growth is unrestricted by the environment or other populations.The larger the population gets, the faster it will grow.

Exponential Growth - A Hypothetical Experiment

A single bacterium divides to produce two cells every 20 minutes. After 20 minutes, under ideal conditions, the bacterium divides to produce two bacteria. After another 20 minutes, those two bacteria divide to produce four cells. After three 20-minute periods, we have 2×2×2, or 8 cells. In one day, this bacterial population will grow to 4,720,000,000,000,000,000,000 individuals. (That’s 4.72 SEPTILLION!)If this growth continued without slowing down, this bacterial population would cover the planet within JUST a few days!

Most populations grow much slower than bacteria…

For example, a female elephant can produce a single offspring only every 2 to 4 years. Newborn elephants take about 10 years to mature.

If exponential growth continued and all descendants of a single elephant pair survived and reproduced, after 750 years there would be nearly 20 million elephants!

Population Growth

1. Exponential Growth→ uninhibited growth→ “J” curve

2. Logistic Growth→ growth is limited→ “S” curve

Logistic Growth: Stage One

Starts off as exponential growth…▪ resources are unlimited

(compared to small population)

▪ few deaths▪ many offspring produced

Logistic Growth: Stage Two

Growth slows down…▪ This happens in all

real-world populations at some time, whether due to limited resources or,

▪ birth rate gets closer to death rate

▪ Population still is growing!

Logistic Growth: Stage Three

Carrying Capacity: The maximum population size an environment can support

What determines carrying capacity?

These are also called LIMITING FACTORS:

1. Density-Dependent Factors→ increase as population increases

▫ Food supply▫ Parasites▫ Disease▫ Competition▫ Predation

2. Density-Independent Factors→ are not affected by population increase or decrease

▫ Rainfall▫ Flood▫ Acidity▫ Drought

Human Population Growth (1950-2050)

Human Population Growth (all history)

What is the carrying capacity of Earth?Most studies put it at 8-10 billion people