Transcript Ch 53 Population Ecology

November 3, 2015
– NEED TEXTBOOK TODAY
Agenda:
• YellowStone and Wolves Video
• Review Ch 52 Synthesis Ques.
• Ch 53 Population Eco Notes –
Lecture and Independent Notes
• Survivorship Curve Practice
Homework:
Finish Ch 53 Notes,
Start Ch 54
Vocabulary (Some
From Project)
Synthesis Worksheet
4 a. DEATH… Less tilt would cause LESS
seasons… warm… longer days….
4 b. Biomes – Less diversity of species, extinction,
adapt
Less tundra and forests
More deserts and grasslands
Chapter 53
POPULATION ECOLOGY
Overview: Earth’s Fluctuating Populations
• How density, dispersion, and demographics can describe a
population.
• The differences between exponential and logistic models of
population growth.
• How density-dependent and density-independent factors
can control population growth.
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
Births and immigration add individuals to a
population.
Births
Concept 52.1: Dynamic
biological processes
influence population density,
dispersion, and demography
Immigration
PopuIation
size
Emigration
Deaths
Deaths and emigration remove
individuals from a population.
Growth Rate = (Birth + Immigration) – (Death + Emigration)
What methods could you use to determine
population density and distribution?
Determining population size and density:
• Count every individual
• Random sampling
• Mark-recapture method (Will practice in class)
Sample Mark and Recapture Scenario
To measure the population density of chipmunks in a
particular park, you sample several plots and capture 50
chipmunks. You mark each of their backs with a small red dot
of paint. The next day, you capture another 50 chipmunks.
Among the 50, you find 10 that are marked.
10
50
=
50
N
N = 250 Chipmunks
What are potential problems that could arise from this method?
What would your solution be to fix them?
Patterns of
Dispersion
• Environmental and social factors influence
the spacing of individuals in a population
 Clumped:
 Uniform
 Is one in which
individuals
aggregate in patches
 May be influenced
by resource
availability and
behavior
 Is one in which
individuals are
evenly distributed
 May be influenced
by social interactions
such as territoriality
 Random
 Is one in which
the position of
each individual
is independent
of other
individuals
Demography: the study of vital statistics that
affect population size
• Life table : age-specific summary of the survival
pattern of a population
Survivorship Curve: represent # individuals alive at
each age
• Type I: low death rate early in life (humans)
• Type II: constant death rate over lifespan (squirrels)
• Type III: high death rate early in life (oysters)
Concept 52.2: Life history traits are products of natural selection
• Natural selection favors traits that will improve an organism’s
survival and reproductive success.
• The traits that affect an organism’s schedule of reproduction and
survival make up its life history.
• Life history includes: When reproduction begins, How often an
organism reproduces, and how many offspring are produced each
time
• Species that exhibit semelparity, or “big-bang”
reproduction
• Reproduce a single time and die
Agave
 Species that exhibit iteroparity, or repeated reproduction
 Produce offspring repeatedly over time
“Trade-offs” between survival and
reproduction • Organisms have finite resources
100
Parents surviving the following winter (%)
80
Male
60
Female
40
20
0
Reduced brood
size
Normal brood
size
Enlarged brood
size
The lower survival rates of kestrels
with larger broods indicate that caring for more
offspring negatively affects survival of the parents.
CONCLUSION
Researchers in
the Netherlands studied the
effects of parental
caregiving in European
kestrels over 5 years. The
researchers transferred
chicks among nests to
produce reduced broods
(three or four chicks),
normal broods (five or six),
and enlarged broods (seven
or eight). They then
measured the percentage of
male and female parent
birds that survived the
following winter. (Both
males and females provide
care for chicks.)
Did you get it?
• Consider two rivers: one is spring fed and is
constant in water volume and temperature year
round; the other drains a desert landscape and
floods and dries out at unpredictable intervals.
Which is more likely to support many species of
iteroparous animals? Why?
Homework:
Life History and Survivorship Curve
Practice
Notes: All starred questions covered in
class. Complete all non-starred items. Ch
53
Chapter 54 Vocabulary
November 4, 2015
• Review the Last of
Population Notes Ch 53
• Weekend HW:
• Population Ecology
Practice Problems
• Inquiry Workbook
Article 4 on Prairie Ckns
• Finish Ch 54/55 Notes
• Work on Project
Warm-Up: How well do we understand the
homework?
A type I survivorship curve is level at first, with
a rapid increase in mortality in old age. The type
of curve is
A. Typical of many invertebrates that produce large numbers of
offspring
B. Typical of large mammals
C. Found most often in r-selected populations with a rapid rate
of reproduction
D. Almost never found in nature
Types of Population Growth
Age Structure Pyramids
(Congo) Potential, ^
Youth: High birth rate,
stable reproductive age
(USA) Slow
growing:
Declining fertility
and mortality
rates, Baby
boomers
(Italy) Low birth
rate, old age
structure,
migration
Zero population growth - birth rate equals the death rate
Population Growth Models
Exponential Population Growth Rate
Concept 52.3: The exponential model describes population growth in
an idealized, unlimited environment.
The rate of reproduction is at its maximum, called the intrinsic rate of
increase or rmax)
dN = popu. size at given time
dt = time
Rmax = max rate
dN =
N = popu size
dt rmaxN
Assumes unlimited
resources.
Though the rate is constant, the population increases exponentially due
to the accumulation of new individuals per unit of time.
Shown in a J-Curve (next slide)
Exponential population growth
• Results in a J-shaped curve
Elephant population
8,000
6,000
4,000
2,000
0
1900
1920
1940
Year
1960
1980
Can indicate rebounding population.
If resources are infinite, what types of species are capable of
exponential growth?
Exponential Growth Problem
Socrative - Sample Problem:
A certain population of mice is growing exponentially.
The growth rate of the population (r) is 1.3 and the current
population size (N) is 2,500 individuals. How many mice
were added to the population the following year?
Did you get it? – Socrative Questions
1. Where is exponential growth in a plant
population more likely: on a newly formed
volcanic island or in a mature, undisturbed rain
forest? Why?
2. In 2006, the USA had a population of about 300
million people. If there were 14 births and 8
deaths per 1,000 people – What was the
country’s net population growth that year?
(Ignore immigration and emigration.)
Concept 52.4: The logistic growth model includes
the concept of carrying capacity
• Exponential growth cannot be sustained for long in
any population
• Logistic Growth Model
• A more realistic population model
• Limits growth by incorporating carrying capacity
• Maximum population size the environment can
support
The Logistic Growth Model
The per capita rate of increase declines as carrying capacity is reached
We construct the logistic model by starting with the exponential model
And adding an expression that reduces the per capita rate of increase as N
increases
K = Carrying capacity
Per capita rate of increase (r)
Maximum
Positive
N
0
Negative
Population size (N)
K
• The logistic model of population growth
• Produces a sigmoid (S-shaped) curve
1,000
800
dN
dt
Population size (N)
1,500
K
1.0N
Number of
Paramecium/ml
2,000
Exponential
growth
1,500
Logistic growth
1,000
dN
dt
1.0N
1,500 N
1,500
500
0
0
Figure 52.12
5
10
Number of generations
15
600
400
200
0
0
5
10
Time (days)
15
• Some populations overshoot K
• Before settling down to a relatively stable density
180
Number of Daphnia/50 ml
150
120
90
60
30
0
0
20
40
60
80
100
120
140
160
Time (days)
Figure 52.13b
A Daphnia population in the lab. The growth of a population of Daphnia in
a small laboratory culture (black dots) does not correspond well to the
logistic model (red curve). This population overshoots the carrying capacity
of its artificial environment and then settles down to an approximately stable
population size.
• Some populations fluctuate greatly around K
80
Number of females
60
40
20
0
1975
1980
1985
1990
1995
2000
Time (years)
Figure 52.13c
A song sparrow population in its natural habitat. The
population of female song sparrows nesting on Mandarte Island,
British Columbia, is periodically reduced by severe winter
weather, and population growth is not well described by the
logistic model.
Did you get it?
Did you get it?
• Explain why a population that fits the logistic
growth model increases more rapidly at
intermediate size than at relatively small or large
sizes.
• Describe what happens to a population as N
approaches K according to the logistic equation.
• What environmental factors stop a population from
growing?
• Why do some populations show radical fluctuations
in size over time, while others remain stable?
K-selection
r-selection
Stable, few offspring
Unstable, many offspring
Live around carrying capacity
Exponential growth
High prenatal care
Little or no care
Low birth numbers
High birth numbers
Good survival of young
Poor survival of young
Density-dependent
Density independent
e.g. Humans
e.g. cockroaches
Type I Survivorship Curve
Type II and III Survivorship Curve
Factors that limit population growth:
• Density-Dependent factors: population matters
• i.e. Predation, disease, competition, territoriality,
waste accumulation, physiological factors
• Density-Independent factors: population not a
factor
• i.e. Natural disasters: fire, flood, weather
Cheetahs are highly territorial
Using chemical communication
to warn other cheetahs of their
boundaries
Factors that regulate populations
Oceanic Birds: Exhibit
territoriality in nesting behavior
Health/Disease
• Density can influence the health and
survival of organisms
• In dense population pathogens can
spread more rapidly
Predation
As a prey population builds
up, predators may feed
preferentially on that
species
Toxic Wastes
The accumulation of
toxic wastes can
contribute to densitydependent regulation of
population size
Intrinsic Factors (Physiological)
Increased population density:
Hormone Fluctuations Weaken Immunity
Sexual organs shrink Stress
Ex. of negative feedback mechanisms
Population Dynamics: A dance of biotic
and abiotic factors
Researchers regularly surveyed the population of moose on Isle Royale,
Michigan, from 1960 to 2003. During that time, the lake never froze over, and
so the moose population was isolated from the effects of immigration and
emigration.
FIELD STUDY
RESULTS
2,500
Moose population size
Over 43 years,
this population
experienced two
significant
increases and
collapses, as
well as several
less severe
fluctuations in
size.
Steady decline probably caused largely by
wolf predation
2,000
1,500
1,000
Dramatic collapse caused by severe winter weather and food
shortage, leading to starvation of more than 75% of the
population
500
0
1960
CONCLUSION
Figure 52.18
1970
1980
Year
1990
2000
The pattern of population dynamics observed in this isolated population
indicates that various biotic and abiotic factors can result in dramatic
fluctuations over time in a moose population.
What do you notice about the population cycles of the
showshoe hare and lynx?
Concepts to Review Independently
• Concept 52.6 Human population growth has
slowed after centuries of exponential increase
• Current Human Population Growth
• No population can grow indefinitely and humans are no
exception
• Global Carrying Capacity
• Ecological Footprint
Did you get it? HANDOUT
Exp. 1
Exp. 2
Exp. 3
Control
Density
A Mortality Density
B Mortality Density
C
Rate
Rate
Rate
Mortality Density
Control
Mortality
Rate
20
0.1
20
0.82
20
0.4
20
0.1
40
0.2
40
0.74
40
0.25
40
0.096
80
0.4
80
0.76
80
0.49
80
0.12
160
0.6
160
0.8
160
0.35
160
0.15
320
0.85
320
0.76
320
0.36
320
0.092