1.Review When do populations grow exponentially

Apply Concepts Why does exponential growth show a characteristic J-shaped curve

2.Review What is the characteristic shape of a logistic growth curve

Explain Describe when logistic growth occurs Form a Hypothesis What factors might cause the

carrying capacity of a population to change.

CH 5 POPULATIONS5.1 How Populations Grow

In the 1950s, a fish farmer in Florida tossed a few plants called hydrilla into a canal

Today, their tangled stems snag boats in rivers and overtake habitats; native water plants and animals are disappearing

Why did they get out of control and what can be done.

Populations

A group of interbreeding individuals of the same type that live in a particular area

Needed to define Type of individual Time Place.

Geographic Range

Area inhabited by a population Range can vary greatly.

Density and Distribution

Population Density The number of individuals per unit area

Distribution How individuals are spaced out across the range:

randomly, uniformly, or clumps.

Random Distribution

Wild flowers grow randomly in a field.

Uniform Distribution

King penguins or a tree farm.

Clumped Distribution

School of fish or pack of wolves.

Population density Number of individuals of a species / (divided by) area

Dispersal Organisms spreading out to other area

Open population Individuals can come and go as they wish

Closed population Individuals must stay within the population.

How do you find the population size

Counting Individuals

Works well for

Limitations Large areas Similar looking organisms Large or small numbers Organisms often don’t stand still while you count.

Sampling Nonmoving Populations

3 Steps Find number of individuals in many smaller

areas Find the population density Multiply by the area.

Nonmoving Population Example

Number of Ponderosa pines in 100,000 acre section of Yellowstone National Park

Plot 1: 20 trees in 1 acre; Plot 2: 10 trees in 1 acre; Plot 3: 30 trees in 1 acre

Number of trees in sampled area60 trees in 3 acres= 20 trees per acre

Total number of trees = average density X area20 trees per acre X 100,000 acres= 2,000,000 trees.

Nonmoving Population Example 2

Number of Ponderosa pines in 100,000 acre section of Yellowstone National Park

Plot 1: 150 trees in 3 acres, Plot 2: 90 trees in 1.5 acres, Plot 3: 60 trees in .5 acre

Number of trees in sampled area150+90+60 = 300 trees 3+1.5 +.5= 5 acres 300 trees per 5 acres = 300/5 = 60 trees per acre

Total number of trees60 trees per acre X 100,000 acres = 6,000,000 trees.

Sampling Moving Populations

Capture Recapture method, catch recatch, tagging Catch a number of individuals from the population,

tag them, record the number of tagged individuals, then release them

Later (time depends on specie) go back to same area and catch individuals, record the total number caught AND the number that you tagged earlier.

Moving Populations Example

How many Walleyes are in Howard Lake Catch, tag, and release 50 walleyes then a week

later catch 60 walleyes, 20 of which are tagged How many walleyes in the lake Use Ratios and cross multiple.

Number caught and tagged

----------------------Total number

Number caught second time that are marked

-----------------------Total number caught

the second time

=

50 walleyes caught1st time

----------------------Total number of

walleyes in the lake

20 tagged walleyesthat were recaught-----------------------

60 walleyes caughtthe second time

=

50 x 60 / 20 = 3000/20 = 150 Walleyes in the lake.

Moving Populations Example 2

How many Rainbow Trout are in a 2 mile section of the Madison River

First time with an electrofisher you catch, clip the adipose fin, and release 100 fish

Second time you get 20 fish 5 of which were marked.

100 trout caught1st time

----------------------Total number oftrout in the river

5 tagged troutthat were recaught-----------------------20 trout caughtthe second time

=

100 x 20 / 5 = 2000/5 = 400 trout in that section of river.

Capture Recapture

Downfalls Electrofisher Catch them all Technique Injuries Length of time between catches Length of time trying to catch.

Population Growth

Tells you if population is growing or not Four rates affect the population size

Mortality Natality Emigration Immigration.

Birthrate and Death Rate Mortality

Death rate, population decreases

Natality Birth rate, population

increases.

Immigration and Emigration

Immigration Individuals move In,

population increases Emigration

Individuals leave, Exit, population decreases.

Age Structure

The number of males and females of each age a population contains

Helps to determine population growth.

Exponential Growth

The larger a population gets, the faster it grows Requires unlimited resources Cannot continue Creates a J Curve.

Organisms in a new environment can grow exponentially for a time.

Logistic Growth

Population’s growth slows and then stops after a period of exponential growth

Happens in natural populations S Curve.

Phase 1

Exponential growth Resources are unlimited, rapid reproduction Low mortality.

Phase 2

Growth slows down Due to high population size and less resources.

Phase 3

Growth stops Population will remain at or near this size

indefinitely.

Analyzing Data

Suppose that a pair of rabbits produces six offspring: 3 male and 3 female and that now offspring die

Calculate If each pair of rabbits breeds only once how many offspring would be produced each year for five years

Interpret Graphs Construct a graph of your data. What type of growth is occurring?

Growth Rate

May go up (+) or down (-) Growth rate = (Natality + Immigration) – (Mortality

+ Emigration)

What is a good growth rate.

Growth Rate Example

Start off with 50 elk

You have 20 elk calves born

You have 4 die of old age

You have 3 that jump the fence and escape

What was your growth rate for the year.

Carrying Capacity

The largest population an area can support forever without harming the environment.