Transcript Population Ecology_AP Bio

Levels of
Organization
•Organism
1
•Population
2
•Community
3
•Ecosystem
4
•Biome
Population Ecology
• Population ecology is the study of populations
in relation to environment
– Including environmental influences on population density
and distribution, age structure, and variations in
population size
Describing
populations
What is a population? What are
the components/characteristics
of a populations?
Population Ecology Topics
1.
2.
3.
4.
5.
6.
Size
Density
Dispersion
Survivorship Curves
Age Structure Diagrams
Growth
–
Exponential, Logistic, Carrying Capacity,
Limiting Factors (density dep, density indep),
Growth Patterns (R and K strategists).
Describing populations
• Size: total # of individuals in a pop (N)
• Density: # / unit area
How big is a population?
Describing populations
Estimation of Population Size
Sampling technique
• Mark and recapture
Describing populations
Mark and Recapture
• Orgs are captured, tagged, and then
released.
• Some time later, the same process is
repeated and the following is used:
Describing populations
• Ex:
– Suppose that 50 zebra mussels are captured,
marked, and released. One week later, 100 zebra
mussels are captured and 10 are found to have
markings already. The estimated population
would then be
• N= (50·100) / (10) = 5000/10 = 500
• N=500
Dispersion
How do
populations
space
themselves?
•
Describes how
individuals in a
population are
distributed in the
environment
1. Clumped
2. Uniform
3. Random
Describing populations
Clumped dispersion
–
–
(most common)
Describing populations
Individuals aggregate in patches
May be influenced by resource availability & behavior
Example:
For many animals, such as these wolves,
living in groups (packs)
1.increases the
effectiveness of hunting.
2.spreads the work of
protecting and caring for
young.
3.helps exclude other
Fish travel in
individuals from their
schools –
territory.
safety in
numbers
Uniform dispersion
Describing populations
-Individuals are evenly distributed
-May be influenced by social interactions such as territoriality
Birds nesting on small islands,
such as these king penguins on
South Georgia Island in the
South Atlantic Ocean, often
exhibit uniform spacing,
maintained by aggressive
interactions between
neighbors.
Some plants
secrete
toxins that
keep others
away
Random dispersion
Describing populations
– The position of each individual is
independent of other individuals
Dandelions grow from
windblown seeds that
land at random and
later germinate.
How do
populations
change over
time?
Changes in Population Size
Describing populations
Biotic potential of a population=
– max rate at which a population could increase under ideal
conditions
•Influenced by several factors:
1. Age at which reproduction begins
2.Life span during which the organisms are capable
of reproducing ( # of reproductive years)
3.Number of reproductive periods in the lifetime
4.Number of offspring the organism is capable of
having
Age Structure
Describing populations
• Description of the abundance
of individuals of each age in a
population.
• Can show changes in a
population
Age Structure Diagrams
2004
China
India
United States
Animation
Describing populations
Survivorship Curves
Describing populations
• Describes how the mortality of individuals in
a species varies during their lifetime
The survivorship
curve for
Belding’s
ground
squirrels
–
Shows that
the death
rate is
relatively
constant
Number of survivors (log scale)
1000
100
Females
10
Males
1
0
2
4
6
Age (years)
8
10
•Type I
•A species in which
most survive to
middle age
•Parenting
•Type II
•Length of
survivorship is
random. Death
rate is constant.
•Type III
Number of survivors (log scale)
• Survivorship curves can be classified into three
general types: Type I, Type II, and Type III
1,000
I
100
II
10
III
1
0
100
50
Percentage of maximum life span
•Most individuals die young.
•Few reach reproductive maturity.
•Fish release 1000s of eggs.
•No parenting
Animation
Survivorship Curves
1) Which curve would fit
an organism that cares for
its young and reproduces
relatively late in life?
Type I
2) Which curve would be typical of an organism that experiences high
predation as small individuals but when they are adults are more able to avoid
most predators?
Type III
3) Which curve might best fit rodents that die in numbers at all ages?
Type II
Factors Affecting
Population
Limiting Factors
Factors Affecting
Population
 Things that prevent a population from
attaining its biotic potential
–
2 categories
1. Density-dependent
2. Density-independent
Density
Dependent
Density
Independent
Density Dependent
Factors Affecting
Population
Populations regulated by density-dependent factors
affected by the number of
organisms present.
are
a)
b)
c)
d)
Predation
Parasitism
Disease
Competition
-the more organisms crowd together, the more damaging are
food shortages, parasites, and predators.
Intraspecific Competition = the
struggle between members of a
population for scarce resources
Density Independent
Factors Affecting
Population
• The number of organisms present does not affect
the influence of the factor.
– Fire, earthquakes, storms, floods
• Density-independent factors show no correlation
with the size of the population.
Describing Population Growth
Population ecologists describe two general patterns of populations
growth:
1. Exponential
2. Logistic
Types of
The growth of a population can be
Population
described by the following equation: Growth
• r= reproductive rate (or population growth)
• N= population size at the beginning of the
interval for which the births and deaths are
counted.
Net increase
of individuals
rmax = births-deaths
.
N
maximum population growth
rate.. growth rate-This is also
known as the “per capita
reproduction rate”….
Population size
Exponential growth
r>0
Types of
Population
Growth
In a population showing exponential growth the
individuals are not limited by food, disease,
predation or competition.
If the rate of reproduction per individual remains
constant through
time, then the
rate at which
the population
increases is a
multiple of the
number of
individuals in
the population.
Exponential population growth
r>0
Types of
Population
Growth
– Results in a J-shaped curve
– Usually short lived in nature- not sustainable
Also called per
capita growth
rate:
dN/dt= rmaxN
(N) (N)
Population size
size
Population
2,000
1,500
dN 1.0N
dt
dN 0.5N
dt
1,000
dN/dt = new
population size
r = growth rate
N= population size
500
0
Mr. Anderson
0
10
15
5
Number of generations
rmax =
Ex:
births-deaths
N
Exponential population growth
% growth per
capita
– A population of 1000 had 60 births and 10
deaths over a one year period. It is experiencing
exponential growth.
# of individuals
– What is the growth rate (rmax)?
added to
population
– 0.05 per year = 5%
– What will be the population next year?
• (dN/dt =rN)
• rN= 50 new individuals
• 1000 + 50 =1050
Exponential population growth
A population is experiencing exponential growth.
Population size = 50
Births = 10
Death = 4
A. Calculate the per capita growth rate (rmax).
– r = (B-D)/N = (10-4)/50 = 0.12
B. Calculate the population growth rate. (Individuals added to the
population in one generation.)
– dN/dt= rmaxN, so 0.12 x 50 = 6
C. What will be the population the next year?
– 50+6= 56
Exponential population growth
A population has no limits on
food, resources, or space:
Population size = 500
Births = 240
Deaths = 170
A. Calculate the r for this population if it is
experiencing exponential growth.
• Answer: 0.14
B. How many individuals will be in the population at
the start of the second generation?
• Answer: 14 x 500 = 70 + 500 = 570
Problem
Exponential population growth
There are 300 falcons living in a certain forest at the beginning
of 2013. Suppose that every year there are 50 falcons born
and 30 falcons that die.
a. What is the population growth rate?
b. What is the per capita growth rate?
c. How many individuals will there be next year?
a. 20
b. 0.067= 6.7%
c. 320
Growth rate
r = births-deaths
N
the real
world
Carrying Capacity (K)
• Populations
usually reach a
carrying
capacity.
• Upper limit to
the number of
individuals the
environment
can support.
Types of
Population
Growth
Logistic growth
In most real populations both food and disease become
important as conditions become crowded.
•A population can grow
exponentially only for
short periods of time,
because it would very
quickly deplete all the
resources necessary for its
survival.
•Over long periods of time,
populations tend to attain an
equilibrium population size
which is determined by the
available resources.
Mr. Anderson
Animation
Types of
Population
Growth
A population is experiencing logistic growth.
Logistic population
growth
Population size = 50
Growth rate is 0.12
Carrying capacity = 400
A. Calculate the population growth rate. (Individuals added to
the population in one generation.)
• dN/dt = rN [(K-N)/K] = 0.12 x 50 x [(400-50/400)] =
5.25
B. This is the same growth rate (r-per capita) as our
exponential growth practice problem. Why is there a
difference in the population growth rate (dN/dt )?
• The 1st pop. was experiencing exponential growth and
the growth rate was not affected by the availability of
resources like space, food, disease, or ability to find
mates. This pop. was affected by the carrying capacity
and this reduced the number of individuals added to the
next generation.
A population B is experiencing logistic growth.
Population size = 500
Growth rate= 0.14
Carrying capacity = 1000
Logistic population
growth
A. How many individuals would be in the population at the
start of the second generation.
• 14 x 500 x [(1000-500)/1000] = 35 + 500 = 535
B. How many individuals would be in the population at the
start of the third generation.
– 570
Life-history
strategies
Logistic and exponential growth are
associated with 2 kinds of life-history
strategies
1.R-selected species (strategists)
• organisms are opportunistic; they reproduce
rapidly when the environment is uncrowned and
resources are vast
2.K-selected species (strategists)
•
operate at a density near K
Animation
R-selected species
Life-history
strategies
a. Opportunistic species, which tend to be colonizers.
b. Grasses, many insects
-Usually quickly invade, reproduce many offspring and die
-Offspring mature quickly and require very little parental
care
c. Strategies for continued existence is based on individuals
having the following traits:
1) small size
2) short life span
3) mature fast
4) produce many offspring
5) engage in little care of offspring
K-selected species
Life-history
strategies
–sensitive to population density
Such populations are equilibrium species, tend to be specialists
rather than colonizers, and may become extinct when their evolved way
of life is disrupted (e.g., the grizzly bear, Florida panther, etc.).
Overall strategy for continued existence is based on having the following
traits:
1) large size
2) long life span
3) slow to mature
4) produce few offspring
5) expend considerable energy in care
Mr. Anderson
Human Population Growth
The following made
exponential growth
possible
1. Increases food supply
2. Reduction in disease
3. Reduction in human
waste
4. Expansion of habitat
As of 12 April 2016 (@ 1:15pm), the human population of
the world is estimated to be 7,415,089,605.
Countries Ranked by Population: 2010
Source: U.S. Census Bureau, International Data Base.
6,817,500,000
Map of countries by population for the year 2015
Equations for Ecology Unit