Ch. 5 Populations

Characteristics of Populations **3 important characteristics of a population are Population Density

Population Growth ** 3 factors can affect pop size: Birth rate Death rate Individuals entering and leaving the pop. * birth rate > death rate = * death rate > birth rate = * birth rate = death rate –

Immigration / Emigration Add or subtract? Emigration

Population Growth Put 4 bacteria cells in a culture of infinite food / unlimited about of bacteria can grow. After 5 mins.  the bacteria reproduce to make 2x the original # of bacteria

Exponential Growth 1 0 min 4 2 5 min 8 3 10 min 16 15 min 32 5 20 min GEN TIME # BACT 1 0 min 4 2 5 min 8 3 10 min 16 15 min 32 5 20 min 64

Does not happen in nature. Why? Exponential growth Happens only at near perfect conditions Does not happen in nature. Why? In natural populations, 100 % of new offspring do not survive to reproduce What adds and subtracts members from a population?

Growth Rate All these factors; birth, death, immigration, and emigration determine growth rate.

Carrying Capacity Carrying Capacity * When death rate = birth rate* at capacity. What factors determine carrying capacity?

2 factors that limit population growth Density – dependent limiting factors

Competition Competition The struggle for use of the same resources that are limited. Animals  Plants  Competition is most fierce between the same species. Why?

Predation All consumers are predators The organism eaten by the consumer Prey Changes in the size of a predator – prey population often occur in cycles. Ex lynx and hare populations

The S – Shaped Curve Population begins to grow – little competition Grows until

Logistic Growth Growth that has a carrying capacity

Density – Independent limiting factors Winters, droughts, seasons Specific organisms – insects and grasses DILF  exponential growth followed by a sudden collapse of the population

Human Population How do factors such as improved medical care and increased availability of food impact the birth rates of humans? Scientist believe the earth’s total carrying capacity for humans is 15 to 20 billion people. What changes in lifestyle would be required in order to accommodate 15 to 20 billion people?

Exponential growth of humans Currently, the human population is growing at an exponential rate. 7 billion now.

Projected Population Growth

Patterns of Population Growth Demography Demographic transition A dramatic change in birth rates and death rates Age – Structure Diagrams

Figure 5-13 Age Distribution Section 5-3 U.S. Population Rwandan Population Males Females Males Females

There must be a carrying capacity. What happens when a population starts to reach it’s carrying capacity? What type of graph represents this? Can you predict what will happen if the population does not level off?