CHARACTERIZATION OF POPULATIONS

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CHARACTERIZATION OF POPULATIONS LAB 4
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Populations can be characterized based on four
main properties

• Distribution
• Density
• Percent Cover
• Dispersion
• A couple of others that are important
• 5. Frequency
• 6. Importance Value

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Four Main Properties
describes the geographical extent of a
population. Its the area or areas where a
species lives and reproduces.
1 - Distribution
2 - Density
of individuals of a species/unit area.
the proportion of organismal density
in an area that can be attributed to one species,
usually expressed as .
Relative density
For example, if half of the plants living in a
meadow are sunflowers, the relative density of
sunflowers is 50, regardless of the absolute
density.

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Relative Density Equation
You try it!
Find the Relative Density for Species C
To express as a , Dr 0.22 x 100 22
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Four Main Properties
3 - Cover the percentage of an area covered
by a species
We can also talk about relative cover
How can it be more than 100?
Relative Cover of Violet
To express as a , Cr .19 x 100 19
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Four Main Properties
4 - Dispersion spacing of individuals of a
population in an area
Clumped where individuals are grouped into
patches. Examples Congregations near areas with
food, shade water. Social
behaviors such as mating time (leks).
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Four Main Properties
4 - Dispersion spacing of individuals of a
population in an area
Random Occurs in the absence of strong
interactions. Examples Resources arent
limiting, so individuals arent
defending territories, etc.
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Four Main Properties
4 - Dispersion spacing of individuals of a
population in an area
Uniform Results from direct interaction between
individs. in pop. Examples Animals defending
territory (i.e., nesting penguins
in packed colonies and each has its little
space).
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5 - Frequency
is a measure of the chance that you will
encounter an individual of the population in one
of your samples.
So if a certain plant occurs in half of your
quadrat samples, the frequency of that plant is
0.50
6 - Importance Value
the sum of the 3 relatives. This
gives an overall estimate of the dominance of a
species.
IV Fr Cr Dr
(Use proportions in this equation)
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So how do we measure all these properties of a
population?
What is a census?
Is it practical?
Remember that to describe a population, we take
samples in order to estimate what that population
is like (Lab 2).
In these cases, n 6
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SAMPLING POPULATIONS

• Which sampling method do we use?
• Some factors that affect the appropriateness of a
  sampling method include
• organism size
• abundance
• mobility of the organism

Sampling Methods for Plants Non-motile Animals
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Types of data collected

• Quadrats
• Numbers
• Size
• cover
• Number of species
• biomass

• Transects
• Density index
• Cover index
• Number of species

Which types of data are comparable across these
sampling methods?
? Relative measures relative species density
and relative cover
So what about dispersion? How do we sample or
measure dispersion?
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How do we determine if a population is clumped,
random, or uniform? Just look at it? How
practical is that? Is there a more rigorous or
precise or mathematical method? We can sample our
population with multiple quadrats Then we can
plot the number of critters (x-axis) vs. the
frequency with which we find that number of
critters in our sample quadrats We generate a
graph that looks like this
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Clumped when a population dispersion is clumped,
most of our sample quadrats will have no
organisms, while a few will have many. (variance
in quadrat counts is high)
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Random when a population dispersion is random,
the relationship between number of individuals
and the number of quadrats with that number of
individuals will follow a Poisson distribution
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Uniform when a population dispersion is uniform,
most quadrats will have the same number of
organisms. (variance in quadrat counts is very
low)
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Graph of probability distribution for of
individuals for uniform, clumped, and random
Most quadrats have about 5 individuals
Most quadrats have 0 or 1 individual, a few have
many
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The Bonus it comes with a t-test!! We can
determine if dispersion is significantly
different from random!
(for todays assignments -- the spreadsheet will
calculate)
Know This!!
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Your (educated) guess?
P gt 0.05, therefore we cannot reject the null
hypothesis
We accept the null hypothesis that Cd 1
Random!!!!
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Your (educated) guess?
P lt 0.05, therefore we reject the null hypothesis
We accept the alternate hypothesis that Cd ? 1
Since Cd ? 1 and is closer to zero than gt1,
Uniform!!!
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Your (educated) guess?
P lt 0.05, therefore we reject the null hypothesis
We accept the alternate hypothesis that Cd ? 1
Since Cd ? 1 and is much gt 1, Clumped!!!
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Assignment Questions 1 8 on page 4-19, 4-20
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Lab exercises We are going to be comparing how
well our sampling methods estimate the actual
population characteristics With this very small
hypothetical population, we can determine the
true population size, density, etc., by census
(done for you), and compare it to our
estimates. We will be using these techniques next
week on Waahila ridge
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Lab exercises - Quadrats

• individual tick marks one unit

• each square is one individual of a given species
• obtain random coordinates (follow instructions
  in manual)
• e.g. x 3, y 5
• plot your 5 x 5 unit quadrat 25 square units
  (u2)

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Lab exercises - Quadrats

• Measurements
• Number of each species (only count if gt 50 of a
  plant is within the quadrat)
• Density of each species (number divided by 25
  u2)
• Total density of the community
• Relative density of each species
• Percent cover of each species
• Relative coverage of each species
• Total coverage of the community
• Calculate population averages

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Lab exercises - Transects

• Generate two pairs of random x-y coordinates
• Flip a coin to determine which of the two will
  be your starting point
• Draw a line 10 units long ( 2.5 inches) from
  your starting point in the direction of your
  other point (NOTE stop your line at 10 units.
  You may go past your other point or you may not
  reach it).

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Lab exercises - Transects

• Measurements
• Number of each species that the transect line
  touches
• Density index for each species (number divided
  by 10 u)
• Total density index of the community
• Relative density index of each species
• Percent cover of each species (the length of
  line that goes over a species divided by the
  total length of line
• Relative coverage of each species
• Total coverage of the community
• Calculate population averages

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• Use Excel spreadsheet to generate
• 25 pairs of coordinates
• Plot out those 25 quadrats and count the number
  of organisms (dots) in each square
• Fill in the frequency table
• Use excel to generate your dispersion graph

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So what do we do with this part?
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Look Closer
In this box, make a rough drawing of what the
curves generated by excel look like
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NEXT WEEK
LAB 5 - WA AHILA RIDGE TRIP I VEGETATION
SAMPLING
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The PowerPoint for next weeks lab is posted on
the website. Your TA will not have time to
spend on a long introduction before you go up the
ridge. You must read and study the PowerPoint
for lab 5 before coming to lab.
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Directions to Waahila Ridge
Your TA may have you meet at the base of the ridge
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Observation climate and vegetation seem to vary
at different elevations on the ridge.
Purpose to identify relationships between
organisms and their environment.
15 - 20 x 20m plots have been established on the
ridge at different elevations
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III. HIKING AND FIELD TRIP REGULATIONS
A. Appropriate Footwear
B. Appropriate Clothing
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