Download Populations

Populations
Chapter 15
Definition
• Population –
• Example –
the human population of Grapevine, TX
Characteristics of Populations
• Population size
– Number of individuals
• Population density
– Number of individuals in an area
• Immigration
– Organisms moving into a population
• Dispersion
– How individuals are arranged in space
Types of Dispersion
Population Growth
= # births - # deaths
– If more individuals are born than die,
the population grows
– If more individuals die than are born,
the populations shrinks
Carrying Capacity (K)
• # of individuals the environment can
sustain
Carrying capacity
What are some factors that would keep a population
from going over their carrying capacity?
Density-Dependent Factors
• Limited Resources
–
–
–
–
–
–
Food
Water
Shelter
Competition
Predation
Parasitism
• When limited resources become depleted,
population growth slows
Population cycles in the snowshoe hare and lynx
Why do the numbers of predators and prey cycle up and down together?
Density-Independent Factors
• Environmental conditions that limit
population growth
– Weather (drought, floods, grass fires)
– Climate
– Human Disturbances
r- and K-Strategists
• r-strategists
–
–
–
–
–
Small
Reproduce often and large numbers
Unstable environment
Exponential growth
ex: mouse, bacteria, rabbits, fish
• K-strategists
– Large
– Reproduce less frequently, in numbers that they can
manage – parental care
– Stable environment
– Logistic growth
– ex: elephant, bears, whales, horses
Populations evolve because
allele frequencies change
• Things that change allele frequencies
– Mutations
– Gene flow
– Non-random mating
– Genetic drift
– Natural selection
Challenge #3
Population Dynamics
T. Trimpe 2008 http://sciencespot.net/
Answer each question.
1. If a population of 50 cottontail rabbits produce 300 young in a year, what is
the birth rate for this population?
2. True or False – If the birth rate < death rate, the population will increase in
size.
3. What term refers to the movement of animals into a population?
Rabbit Population
Rabbit Population Study
4. Use the graph to answer these questions.
B. In which year did the population increase
the most?
500
# of Rabbits
A. In which year did the population decrease
the most?
Data recorded at the end of each year.
600
400
300
200
100
0
1
2
3
4
5
6
Year
7
8
9
10
The answers are …
1. If a population of 50 cottontail rabbits produce 300 young in a year, what is
the birth rate for this population?
300 rabbits per year
2. True or False – If the birth rate < death rate, the population will increase in
size.
False – The population would decrease.
3. What term refers to the movement of animals into a population?
Immigration
Rabbit Population
Rabbit Population Study
4. Use the graph to answer these questions.
B. In which year did the population increase
the most?
Year 1
500
# of Rabbits
A. In which year did the population decrease
the most?
Year 4
Data recorded at the end of each year.
600
400
300
200
100
0
1
2
3
4
5
6
Year
7
8
9
10
Gene Flow
• Migration of fertile
individuals or
gametes between
populations
• Reduces differences
between populations
Genetic Drift
Change in allele frequency due to chance.
Happens in small populations.
Bottleneck Effect
(Genetic Drift)
Preserving Variation
• Why are unfavorable alleles not eliminated
from population?
• Diploidy
• Heterozygote advantage
– Ex: sickle-cell allele and malaria
Natural Selection
• Darwinian fitness – contribution an
individual makes to the gene pool of the
next generation relative to the
contributions of others
• Modes of selection
– Directional
– Diversifying
– Stabilizing
Modes of Selection
Directional Selection
Diversifying Selection
A limited resource is known as a
A.
B.
C.
D.
Polygenic trait
Logistic model
Density-independent factor
Density-dependent factor
An organism that grows
exponentially is
A.
B.
C.
D.
Dispersed
Polygenic
An r-strategist
A K-strategist
_____ tends to happen in a
population whose individuals have
extreme traits.
A.
B.
C.
D.
Random mating
Directional selection
Stabilizing selection
Exponential growth
A colony of bacteria that has limited
food will undergo ______ growth.
A.
B.
C.
D.
Exponential
Logistic
Natural
random
Which of the following is not a
cause of genetic change?
A.
B.
C.
D.
Genetic drift
Random mating
Natural selection
mutation