Populations

Review What is a population? A population consists of multiple individuals belonging to the same species, living in the same area at the same time Three important characteristics of a population are its:

1. Geographic Distribution This is the geographic range that the population inhabits In other words, this is where in the world that species is found

2. Density Which side has a higher density? Population density is the number of individuals per unit area This describes how closely packed together the individuals of a population are A B

3. Growth rate The growth rate is the increase or decrease of the number of individuals in a population over time

3 factors that affect population growth Number of births Number of deaths Number of individuals that enter or leave the population Immigration: entering Emigration: leaving Births Deaths Immigration Emigration

Therefore… A population grows when: A population shrinks when: Birth rate > death rate Immigration > emigration A population shrinks when: Birth rate < death rate Immigration < emigration

Two Types of Growth rates Exponential Growth: occurs when individuals of a population reproduce at a constant rate Logistic Growth: occurs when a population’s growth slows or stops following a period of exponential growth

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially Do you think this type of growth is common in nature? Why or why not?

Logistic Growth As resources become less available, the growth of a population slows or stops Carrying capacity is the largest number of individuals of a population that a given environment can support