Populations
3.
A population
is a group of
individuals of
the same
species
living in an
area
1
Distribution Patterns
Populations disperse in a variety of ways that
are influenced by environmental and social
factors
• Uniform distribution results from
intense competition or
antagonism between individuals.
• Random distribution occurs
when there is no competition,
antagonism, or tendency to
aggregate.
• Clumping is the most common
distribution because
environmental conditions are
seldom uniform.
2
What causes these populations of different organisms
to clump together?
Clumped distribution
in species acts as a
mechanism against
predation as well as an
efficient mechanism to
trap or corner prey. It
has been shown that
larger packs of animals
tend to have a greater
number of successful
kills.
Fig. 52.1, Campbell & Reece, 6th ed.
Population Dispersal
• Natural range expansions show the influence of
dispersal on distribution
– For example, cattle egrets arrived in the Americas
in the late 1800s and have expanded their
distribution
4
Population Dispersal
• In rare cases, longdistance dispersal
can lead to adaptive
radiation
– For example,
Hawaiian
silverswords are a
diverse group
descended from
an ancestral North
American tarweed
5
Estimating Population Size
The Mark-and-Recapture Technique
2.
1.
3.
6
Estimating Population Size
The Mark-and-Recapture Technique
• There’s a simple formula for estimating the total
population size
𝑠 𝑥
=
𝑁 𝑛
s = Number of individuals marked and released in 1st sample
x = Number of individuals marked and released in 2nd sample
n = Total number of individuals in 2nd sample
N = Estimated population size
Rearrange to get:
𝑁=
𝑠𝑛
𝑥
7
Let’s Try an Example!
• Twenty individuals are captured at random
and marked with a dye or tag and then are
released back into the environment.
• Therefore s = # of animals marked = 20
• At a later time a second group of animals is
captured at random from the population
8
Let’s Try an Example!
• Some will already be marked, say 10 individuals
were marked out of 35 that were captured the
second time. We now know n = 35 and x = 10
• So, apply the formula and solve for the estimated
population size:
𝑁=
𝑠𝑛
𝑥
=
20 35
10
=
700
= 70
10
Therefore, N = 70 as a population estimate
9
Which method would you use?
1. To determine the number of deer in the state of
Virginia?
2. To determine the number of turkeys in a county?
3. To determine the number of dogs in your
neighborhood?
4. To determine the number of ferrel cats in your
neighborhood?
10
Survivorship curves
1000
What do these graphs
indicate regarding species
survival rate & strategy?
Human
(type I)
I. High death rate in
post-reproductive
years
Hydra
(type II)
Survival per thousand
100
II. Constant mortality rate
throughout life span
Oyster
(type III)
10
1
0
25
50
75
Percent of maximum life span
100
III. Very high early
mortality but the few
survivors then live long
(stay reproductive)
Number of survivors (log scale)
Ideal Survivorship Curves
I
1,000
100
II
10
III
1
0
50
Percentage of maximum life span
100
Population Growth Curves
𝑑𝑁
=𝐵−𝐷
𝑑𝑡
d = delta or change
N = population Size
t = time
B = birth rate
D =death rate
13
Population Growth Models
Exponential model (blue)
idealized population in an unlimited
environment (J-curve); can’t
continue indefinitely.
r-selected species (r = per capita
growth rate)
𝑑𝑁
= 𝑟𝑚𝑎𝑥 𝑁
𝑑𝑡
Logistic model (red) considers
population density on growth
(S-curve), carrying capacity (K):
maximum population size that a
particular environment can support;
K-selected species
𝑑𝑁
𝐾−𝑁
= 𝑟𝑚𝑎𝑥 𝑁
𝑑𝑡
𝐾
Exponential Growth Curves
Growth Rate of E. coli
d = delta or change
N = Population Size
t = time
rmax = maximum per
capita growth rate
of population
Population Size, N
𝒅𝑵
= 𝒓𝒎𝒂𝒙 𝑵
𝒅𝒕
Time (hours)
15
Logistic Growth Curves
• In the logistic population growth model, the per
capita rate of increase (rmax) declines as carrying
capacity (K) is reached
• The logistic model starts with the exponential
model and adds an expression that reduces per
capita rate of increase as N approaches K
𝑑𝑁
𝐾−𝑁
= 𝑟𝑚𝑎𝑥 𝑁
𝑑𝑡
𝐾
16
Logistic Growth Curves
𝑑𝑁
𝐾−𝑁
= 𝑟𝑚𝑎𝑥 𝑁
𝑑𝑡
𝐾
d = delta or change
N = Population Size
t = time
K =carrying capacity
rmax = maximum per
capita growth rate
of population
17
Comparison of Growth Curves
18
Growth Curve Relationship
19
Examining Logistic Population Growth
Graph the data
given as it
relates to a
logistic curve.
Title, label and
scale your graph
properly.
20
Examining Logistic Population Growth
Hypothetical Example of Logistic Growth Curve
K = 1,000 & rmax = 0.05 per Individual per Year
21
Population Reproductive Strategies
• r-selected
(opportunistic)
• Short maturation & lifespan
• Many (small) offspring;
usually 1 (early) reproduction;
• No parental care
• High death rate
• K-selected
(equilibrial)
• Long maturation & lifespan
• Few (large) offspring;
usually several (late)
reproductions
• Extensive parental care
• Low death rate
How Well Do These Organisms Fit the
Logistic Growth Model?
Some populations overshoot K
before settling down to a
relatively stable density
Some populations fluctuate greatly and
make it difficult to define K
23
Age Structure Diagrams: Always Examine The Base Before
Making Predictions About The Future Of The Population
Rapid growth
Afghanistan
Male
Female
10 8
6 4 2 0 2 4 6
Percent of population
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
8 10
8
Slow growth
United States
Male
Female
6 4 2 0 2 4 6
Percent of population
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
8
8
No growth
Italy
Male
Female
6 4 2 0 2 4 6 8
Percent of population
Natural Selection
• This includes describing how organisms respond
to the environment and how organisms are
distributed.
– Events that occur in the framework of ecological time
(minutes, months, years) translate into effects over
the longer scale of evolutionary time (decades,
centuries, millennia, and longer).
25
Natural Selection
26
Finch Beak Size or Shape
27
Modes of Selection
http://gregladen.com/blog/2007/01/the-modes-of-natural-selection/
28
Modes of Selection
Disruptive- produces a bimodal curve as the extreme
traits are favored
Stabilizing-reduces variance
over time as the traits move
closer to the mean
Directional-favors a
phenotypic trait (selected by
the environment)
Introduced Species
• What’s the big deal?
• These species are free from
predators, parasites and pathogens
that limit their populations in their
native habitats.
• These transplanted species
disrupt their new community by
preying on native organisms or
outcompeting them for
resources.
30
Guam: Brown Tree Snake
• The brown tree snake was
accidentally introduced to
Guam as a stowaway in
military cargo from other
parts of the South Pacific
after World War II.
• Since then, 12 species of
birds and 6 species of lizards
the snakes ate have become
extinct.
• Guam had no native snakes.
Dispersal of Brown Tree Snake
31
Southern U.S.: Kudzu Vine
• The Asian plant Kudzu was introduced by the U.S. Dept.
of Agriculture with good intentions.
• It was introduced from Japanese pavilion in the 1876
Centennial Exposition in Philadelphia.
• It was to help control erosion but has taken over large
areas of the landscape in the Southern U.S.
32
Introduced Species
33
New York: European Starling
• From the New York Times, 1990
The year was 1890 when an eccentric drug manufacturer named
Eugene Schieffelin entered New York City's Central Park and
released some 60 European starlings he had imported from England.
In 1891 he loosed 40 more. Schieffelin's motives were as romantic as
they were ill fated: he hoped to introduce into North America every
bird mentioned by Shakespeare.
Skylarks and song thrushes failed to thrive, but the enormity of his
success with starlings continues to haunt us. This centennial year is
worth observing as an object lesson in how even noble intentions can
lead to disaster when humanity meddles with nature.
34
New York: European Starling
• From the New York Times, 1990 (cont.)
Today the starling is ubiquitous, with its purple
and green iridescent plumage and its rasping,
insistent call. It has distinguished itself as one
of the costliest and most noxious birds on our
continent.
Roosting in hordes of up to a million, starlings
can devour vast stores of seed and fruit,
offsetting whatever benefit they confer by
eating insects. In a single day, a cloud of
omnivorous starlings can gobble up 20 tons of
potatoes.
35
Zebra Mussels
• The native distribution of the
species is in the Black Sea and
Caspian Sea in Eurasia.
• Zebra mussels have become an
invasive species in North America,
Great Britain, Ireland, Italy, Spain,
and Sweden.
• They disrupt the ecosystems by
monotypic (one type) colonization,
and damage harbors and
waterways, ships and boats, and
water treatment and power plants.
36
Zebra Mussels
• Water treatment plants are
most impacted because the
water intakes bring the
microscopic free-swimming
larvae directly into the
facilities.
• The Zebra Mussels also cling on
to pipes under the water and
clog them.
• This shopping cart was left in
zebra mussel-infested waters
for a few months. The mussels
have colonized every available
surface on the cart.
(J. Lubner, Wisconsin Sea Grant,
Milwaukee, Wisconsin.)
37
Zebra Mussel
Range
38
Relationship Between Temperature and Precipitation
39