BIO 101: FA12
Bio 101: What is Science? How do individuals in a population
interact?
Class Meeting: Friday, 31 August 2012
Announcements:
 HW3:
Practicing decifering experimental designs with cane toad paper. Pushed
back to Wednesday 9/5/12 before class. We will practice this in class
today.
 A great place for more information on the process of
science!
http://undsci.berkeley.edu/article/intro_01
 HW4: due next Wednesday. We will talk about that later today.
 HW5: Group contract. Will have assignment and sample contract up this afternoon. Due next Friday (9/7/12)
 My office is changing. I am now in Biology 1112B (1st floor office suite)
Objectives:
 Distinguish questions that can be answered
scientifically from those that cannot. Given a question
or results from a "study" explain whether the results or question can
or cannot be answered scientifically. chapter 1
 Identify the pattern of scientific reasoning
and investigation. Given a question/statement, create a testable
hypothesis including...
 Null and alternative hypotheses
 Independent and dependent variables
Given an experimental design identify those same elements. Cane
toad paper Chapter 1
 Distinguish the difference among
Observations, hypotheses, and theories. Given a
statement identify whether it is an observation, hypothesis or theory.
Be prepared to explain your rational Chapter 1
 Determine whether a hypothesis has been supported through
statistics using a pvalue.
Given a hypothesis with a pvalue, state whether the hypothesis has
been supported.
 Identify
the relationship
between births and deaths that result in population change.
given the birth rate and death rate determine whether a population is
increasing or decreasing in size. determine the number of eggs
surviving to reproductive age to maintain a population. chapter
36
 Reproduce/identify exponential
and logistic growth curves and
all important features relative to both (including growth phases and
carrying capacity). Given a population, show an expected growth curve
and identify the important points in the curve. given a scenario
determine whether the population is under exponential or logistic growth Chapter
36
 Identify
the intrinsic
characteristics of growth (includes
r vs k strategies). Given an organisms life history is it likely an r
or K strategist. Given environmental conditions predict whether r or k
strategists are more likely to succeed. for a given r is the population
increasing, decreasing, or stable? Chapter
36
 Distinguish
between density
dependent and density independent limiting factors.
Given a population list a density dependent and density independent
limiting factor. State whether the factor is biotic or abiotic. Explain
your answer. chapter
36
cane Toad Video
Evaluating Data
Objective(s): 1, 2
Scientific tests must have clearly defined variables and a null
hypothesis
Types of variables
 Dependent  What investigator
thinks is affected (plotted on yaxis)(effect)
 Independent  Often what the
investigator varies/manipulates, usually cause (plotted on
xaxis)(cause)
 Controlled  Variables held
constant (control for other alternative hypotheses)
the independent variable causes the dependent response
What is a null hypothesis?
 H_{0} (Null hypothesis) = no
difference, independent does not effect dependent
 H_{A} (alternate hypothesis) = a
difference exists, a relationship exists, independent causes change in
dependent
Sample experiment: 12 plants:
6 with nutrients added, 6 with no nutrients added, measure
growth (grams biomass) after 6 weeks. Water same amount, keep at same
temperature, give same amount of light
 List the alternative hypothesis: plants
that receive nutrients will have higher biomass than plants that do not
receive nutrients(note that plants that receive nutrients will have
lower biomass is another alternative hypothesis)
 List the null hypothesis: plants
that receive nutrients will have the same biomass as plants that
receive no nutrients (only one null hypothesis)
 List the dependent, independent and any control variables
 Dependent variable: Plant biomass at
6 weeks (in grams)
 Independent variable: Nutrient
addition (treatment groups: with nutrient addition, without nutrient
addition)
 Control variables: water,
temperature, light
Pvalue
Objective(s): 4
Scientists use pvalues to provide information on the
probability that
a relationship occurred by chance. The higher the pvalue, the less
likely that the independent variable caused the change in the dependent
variable (ie the relationship is not significant).
If the pvalue <0.05, then there is less than a 5% chance that
the difference seen or relationship observed was caused by
chance alone.
so...
pvalue >=0.05
then not significant
pvalue < 0.05 then significant
Note: Error bars (vertical lines in the graphs below) show how much
variability is in the values used to calculate a mean. If the
error
bars overlap, the differences probably are not significant.
small error bars that do not overlap
p<0.05 maybe p=0.005 
error bars overlap and extend beyond average represented by bar
p>0.05, maybe p=0.08 
Clicker questions
Objective(s): 2, 3, 4
Passages from Cane Toad Paper (Brown et al 2007)
para 1 pg 17698, fig 2a. size
The arthritic condition is absent in smaller toads
(logistic regression with toad body size vs. arthritis occurrence: X^{2}
= 13.94; df = 1; P < 0.0002; see Fig. 2A).
1. Independent Variable
2. Dependent Variable
3. Control Variable 
a.
whether the toads have arthritis
b. there are none evident from the
statement
c. small toads
d. large toads
e. toad size
f. none of the toads had arthritis
g. both toad types had the same amount
of arthritis
h. toads with arthritis
i. toads without arthritis 
para 1 pg 17698, fig 2a. size
The arthritic condition is absent in smaller toads
(logistic regression with toad body size vs. arthritis occurrence: X^{2}
= 13.94; df = 1; P < 0.0002; see Fig. 2A).
4. Null Hypothesis
5. Alternative Hypothesis
6. Was the alternative hypothesis supported (significant or not
significant) 
a. there
are none evident from the
statement
b. large toads have more arthritis than
small toads
c. none of the toads had arthritis
d. both toad types had arthritis
e. both toad types had the same amount
of arthritis 
Radiotracking
of freeranging toads shows that the arthritic animals continue to move
at least as far and fast under field conditions as do nonaffected
conspecifics (mean distances 157 vs. 144 m per day respectively, based
on 11 pairs of sizematched animals monitored over the same time
periods: F1,20=0.06; P=0.81).
1. Independent Variable
2. Dependent Variable
3. Control Variable 
 whether the toads have arthritis
 none of the toads traveled
 time period sampled, toad size
 distance traveled
 toads with and without arthritis travel the same
distance
 arthritic toads
 nonarthritic toads
 long distance traveled
 there are none evident from this statement

Radiotracking
of freeranging toads shows that the arthritic animals continue to move
at least as far and fast under field conditions as do nonaffected
conspecifics (mean distances 157 vs. 144 m per day respectively, based
on 11 pairs of sizematched animals monitored over the same time
periods: F1,20=0.06; P=0.81).
4. Null Hypothesis
5. Alternative Hypothesis
6. Was the alternative hypothesis supported (significant or not
significant) 
 whether the toads have arthritis
 none of the toads traveled
 toads with and without arthritis travel the same
distance
 toads without arthritis travel a longer distance than
toads with arthritis
 arthritic and nonarthritic toads both travel long
distances

Q1  What do you need to know to predict population
change?
objective: 4, 7
As a group, on paper, answer the following questions regarding the deer
population scenario.
You are responsible for maintaining the deer herd of Kentucky. Answer
the following questions to predict next years population size.
 What limits deer population size?
 What increases deer population size?
 What counts from this year do you need to know?
 What rates do you need to know?
 Is there anything else you need to know?
What factors determine population growth rate?
objective: 4, 6
Population growth rate depends on
 the current size of the population
 the contribution of each individual
to
the population growth rate
 survival/death rate
Intrinsic growth rate of a population
depends on the species.
Intrinsic growth = how fast a population can grow.
Pianka
ER.
1988. Evolutionary Ecology. New York: Harper Collins Publishers Inc. p.
140
Pianka
ER.
1988. Evolutionary Ecology. New York: Harper Collins Publishers Inc. p.
162
When does a population size change?
objective: 4, 5
births = deaths, the population size stays the same [zero
population growth]
births>deaths, the population size increases
births<deaths, the population size decreases
"r" = per capita rate of increase
Within populations, r varies through time and can be
positive
(increase), negative (decrease) or zero (no change).
Exponential growth
If all individuals are reproducing at their maximum
potential,
the population size increases exponentially.
Figure 52.5 Freeman 2005
Population growth model
objective: 4, 6, 7
Population  a group of
organisms
of the same
species within a defined area. Often the population is determined by
the question being asked. (ie the kentucky deer population,
population of bacteria in a test tube, population in a river or bay)
Variables
 r_{d}
=
death rate (deaths per unit time ie year)
 r_{b}
=
birth rate (births per unit time ie year)
 n_{1}
=
population size at time 1 (number of individuals in population now)
 n_{2}
=
population size at time 2 (number of individuals in population 1 year
from now)
Survival and reproductive success depends upon
 biotic factors  living
things
such, competition, predation, and food production
 abiotic factors 
nonliving
things such as weather, water availability, and nutrient availability
with this information you can calculate the number of
individuals at the end of one unit of time.
number of
births 
 
number of
deaths 
+ 
population
at start 
= 
population in one year 

r_{b}*n_{1} 
 
r_{d}*n_{1} 
+ 
n_{1} 
= 
n_{2} 
note: the book uses r. r = intrinsic growth rate = r_{b}
 r_{d}
therefore we can rewrite our equation as:
What is in these carboys?
objective: 4, 5, 7
 If left in a wort (sugar solution used to grow yeast),
predict the change in population size in the carboy over time (draw
figure)
 Will the population increase indefinitely? Why or why not?
 Identify the different phases of growth in your diagram and
identify any biotic or abiotic factors that may be affecting growth
Do most natural populations exhibit exponential growth? Why?
objective: 5, 7
Logistic growth
objective: 5
Figure 52.5 Freeman 2005
What limits growth rates and population size?
objective: 7
Densityindependent factors
 change birth rates and death rates regardless of the
number of individuals in the population.
 usually triggered by changes in abiotic environment
(environmental resistance)
 Weather including hurricanes
 volcanoes
 forest fire
 pollution
Densitydependent factors
...usually biotic and change in intensity as a function of
population size.
e.g., increase in intensity as population size
approaches carrying capacity.
Carrying capacity depends upon the quality of the habitat.
e.g., predation
e.g., trees: if crowded have less sunlight, nutrients,
water  therefore produce fewer seeds.
(competition for resources)
How does carrying capacity fit into our prior growth model?
New variables
 K = carrying capacity =
maximum sustainable population size
 G = population growth = growth
including other factors (ie K )
Exponential growth model 
G=rN 
Logistic growth model 
G=rN[(KN)/K] 
r & k strategies
objective: 4, 5, 6, 7
 Imagine a site where every day there is abundant food, but
organisms are likely to be killed getting the food. Which organism
would you expect have more offspring?
 hundreds of offspring, little parental care
 only a few offspring, lots of parental care/teaching
 Assuming
that reproductive aged adults are likely to survive and reproduce,
would it make more sense for an organism to have lots of offspring if a
site is stable or if a site is unpredictable?
r & k strategies
objective: 4, 5, 6, 7
 r strategist
 r because (intrinsic growth rate) maximized
 little parental care
 high mortality rate
 short lived
 k strategist
 k because tends to live near carrying capacity
 large bodies
 long life
 few, well cared for offspring
Name three examples of rstrategists and three examples of
kstrategists in your groups
r & k strategies
objective: 4, 5, 6, 7
 Examples
 r = cockroach, rat, dandelion
 k = elephant, human, coconut
 r and k strategies are extremes and most organisms fall
somewhere in the middle
 r
strategists tend to favor areas with high disturbance, k strategists
often have difficulty surviving in areas with frequent disturbance
 Humans tend to cause frequent disturbance, hence we tend to
encourage rstrategist organisms (see list above)
Modeling deer population growth
objective: 4, 5, 6, 7
birth rate = 1.5 faun per female
percent of births male = 50%
r_{dn} = natural death rate = 10% of total deer
population
r_{dh} = harvest rate = 15% of total deer
population (can be divided among males and females differently)
n_{1} = deer population size at year 1 = 10,000
(6,000 female, 4,000 male) Here is a relatively simple
example using a spreadsheet
Population counter
Analyzing the change in the growth rate of human populations:
From Freeman 2005, Figure 52.13
Scenario depends on female fertility rate  now 2.7 worldwide.
Replacement rate: if at zero for one generation, r=0, ZPG
(Zero Population Growth).
Homework 4: design an experiment: step 1
to
be complete next week, so think about ideas over the weekend. The
hypothesis does not have to be biologically related and must be
completed within 1 week.
As a group, submit online in Blackboard
 Observation:
 What observation/s did you make that lead to your
question?(ie Why are you interested in this problem?)
 Question:
 What is your research question?
 Hypothesis: how will you test your question?
 Write out the hypothesis
 List your dependent variable  response  needs to be
quantifiable (counts, measurement, time, etc)
 List your Independent variable  the cause  can be
manipulated or observed
 List any controls  accounts for any competing
hypotheses
 Describe your proposed Method 
 How will you carry out the experiment
 There should be replication
Note 1: Do not conduct the experiment
yet You will conduct the experiment in Part 2.
Note 2: Do not use Human Subjects in your
experiment unless you are only observing. Do not use
vertebrates, including fish
in your study unless you are only observing. Therefore, no surveys and
no asking other students to be in your study and no using pets (unless
you have a pet snail, cricket or amoeba).
Rubric for
homework
 1 pt  Assignment completed on blackboard ontime
 1 pt  Observations lead to testable hypothesis
 1 pt  Identifies dependent and independent variables
 1 pt  Description of experiment would allow another
student to repeat the experiment
 1 pt  Experiment includes replication  more than one
sample per treatment