POPULATIONS Definition All the members of a species

POPULATIONS Definition: All the members of a species that live in one place at one time.

PROPERTIES of Populations Geographic dispersion—the way in which individuals of a population are spread in an area or volume. Eg. Bears, owls, tigers Eg. Dandelions Eg. Wolves, bison, elephants

Population Growth SIZE Definition n Population SIZE ¡ The number of individuals in a population

Population Size n Depends on: ¡ ¡ Birth + Death Emigration: movement of individuals OUT OF a population Immigration: movement of individuals INTO a population +

Population Size Calculation n What if there were 1267 rabbits in a colony. In one year 1500 rabbits were born, 1285 died, 65 emigrated and 0 immigrated. What is the new size of the population? Answer: 1417 By how much did the population grow? ¡ 150 What would the number look like if there was a decline in population growth? ¡ Negative number ¡ n n

Population Growth RATE Population growth RATE ¡ The amount by which a population’s size changes over time.

2 Types of Population Growth Rate 1. 2. Exponential Logistic

EXPONENTIAL Model of Population Growth n n A population grows exponentially when resources are abundant. If a population grows exponentially the population size increases dramatically over a period of time.

Do the Math n Fill in the chart with the correct quantities Time (minutes) 0 20 40 60 80 100 120 140 160 180 200 Formula Number of Cells 20 21 22 23 24 25 26 27 28 29 210 1 2 4 8 16 32 64 128 256 512 1024

Positive Feedback n Exponential growth is an example of positive feedback. ¡ The more organisms there are, the more babies will be born who, in turn, grow up to have babies themselves and so on.

Positive Feedback n Positive feedbacks can be expressed in graph form as well. “J” shaped curve

Exponential Growth Curve n n n Trace the trend line for the exponential growth curve and label the x and y axes with appropriate terms and Add a title

n Time vs. Number of Individuals

Logistic. Model of Population Growth n n n Exponential growth is not sustainable long term!!! Most populations will face limiting factors and thus show a “logistic” growth rate. Populations are limited by finite resources in the environment.

Logistic Population Growth The amount of resources in an environment dictates its carrying capacity. Definition of Carrying Capacity: The number of individuals the environment can support over a long period of time. • Based on the amount of resources in that environment.

Logistic Growth Curve n n On your notes trace the trend line Label the x and y axis Add a title Label the phrases ¡ Birth rate increases ¡ Death rate increases ¡ Carrying capacity

LOGISTIC Model of Population Growth When at carrying capacity, birth rate is equal to death rate As population reaches carrying capacity, death rate increases “S” When. Stretched populationout is small, birth rate is higher than death rate

Logistic Growth Curve n According to the graph, how many individuals will this environment “carry” for the long term? ¡ 2. 50 thousand

Negative Feedback Logistic growth is an example of negative feedback. n Since resources are limited, there is competition for these resources, therefore death rates rise, causing the population to stabilize.

Negative Feedback n Negative Feedback Loops can be expressed in graph form-the graph is shaped like the letter “S” (logistic).

Logistic Growth Curve n n Often the population Carrying Capacity oscillates up and down, but there is an overall equilibrium to the population. Draw in the carrying capacity line in your notes

Logistic Growth Curve n The carrying capacity is around 1. 5 million individuals

Negative Feedback Limiting factors cause negative feedback loops. There are 2 types of limiting factors: 1. Abiotic n Examples of abiotic limiting factors ¡ ¡ temperature Space

Negative Feedback 2. Biotic factors n Examples of biotic limiting factors ¡ ¡ Food Disease

Population DENSITY n Definition: Population DENSITY Number of individuals per unit of area Low density High density

Do the math n In a 3 km 2 area there are 7 deer. What is the density of the deer population? ¡ Answer: 2. 3 deer/km 2

Population Size REGULATION 1. Density Independent Factors: factors that reduce population regardless of population size Examples: ¡ Weather ¡ Fires ¡ Floods

Population Size REGULATION 2. Density Dependent Factors: triggered by increasing population density Examples ¡ Food shortages ¡ Space limitations ¡ Waste accumulation