population ecology. definition of population: group of individuals of a single species living in a...
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Population Ecology
Definition of Population:
• Group of individuals of a single species living in a specific geographic region at the same time
Study of populations in relation to environment
– Environmental influences on:• population density • age structure• population distribution (dispersion)
• Density is the result of a dynamic interaction of processes that add individuals to a population and
those that remove individuals from itBirths and immigration add individuals to a population.
Births Immigration
PopuIationsize
Emigration
Deaths
Deaths and emigration remove individuals from a population.
How do these factors Contribute to Population Size??
• Births• Deaths• Immigration• Emigration
Clumped Dispersion
– Individuals aggregate in patches– May be influenced by resource availability
and behavior
Uniform Dispersion– Individuals are evenly distributed– May be influenced by social interactions
such as territoriality
Random Dispersion
• Position of each individual is independent of other individuals
(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.
How do wildlife biologists quantify populations?
Defined Populations-complete counts-incomplete counts-indirect counts
Undefined Populations
Mark and Recapture
Life history traits are products of natural selection
• Life history traits are evolutionary outcomes– Reflected in the development, physiology, and
behavior of an organism
• Three things needed quantify life historyi. When reproduction beginsii. How often organism reproducesiii. How many offspring produced
Semelparity: Big Bang– Reproduce a single time and die
– putting all available resources into maximizing reproduction at the expense of future life
Iteroparity – Repeated Reproduction– produce offspring repeatedly over time– increased parental care along with
enhanced energetic investment per offspring
“Trade-offs” and Life Histories• Organisms have finite resources
The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents.
CONCLUSION
100
80
60
40
20
0
Reduced brood size Normal brood size Enlarged brood
size
Par
ents
sur
vivi
ng th
e fo
llow
ing
win
ter
(%)
Male
Female
– Which may lead to trade-offs between survival and reproduction
RESULTS
– Kestrels:
• Produce a few eggs?
– Can invest more into each, ensuring greater survival
• Produce many eggs?
– Costly but if all survive, fitness is better
More is Better?• Some plants produce a large number of small
seeds– Ensuring that at least some of them will
grow and eventually reproduce
Fewer is Better?
• Other types of plants produce a moderate number of large seeds
– That provide a large store of energy that will help seedlings become established
Demography
• Study of the vital statistics of a population– And how they change over time
• Death rates and birth rates
• Zero population growth – Occurs when the birth rate equals the death
rate
Exponential Population Growth
Population increase under idealized conditionsNo limits on growth
• Under these conditions– The rate of reproduction is at its maximum,
called the intrinsic rate of increase
Example-understanding growth
Question: I offer you a job for 1 cent/day and your pay will double every day. You will be hired for 30 days. Will you take my job offer?
Answer: If you said YES, you will have made $~21 million dollars for 30 days of work.
How is this possible?????
1ST DAY OF WORK: 1 cent pay/day
30TH DAY OF WORK: ~10.2 million/day
How is this possible?????
Am
ou
nt
of
Pay/D
ay
# of Days
Exponential Growth Model*Idealized population in an unlimited
environment
*Very rapid doubling time; steep J curve
*r=N=(b-d)N tr=instrinsic rate of growth
dNdt rmaxN
Exponential Growth in the Real World
• Characteristic of some populations that are rebounding
1900 1920 1940 1960 1980Year
0
2,000
4,000
6,000
8,000
Ele
phan
t po
pula
tion
–Cannot be sustained for long in any population
Logistic Population Growth
• More realistic model of population growth
• Carrying capacity (K)– Is the maximum population size the
environment can support
• In the logistic population growth model– The per capita rate of increase declines as
carrying capacity is reached
Logistic Population Growth
– Produces a sigmoid (S-shaped) curve
Figure 52.12
dN
dt 1.0N Exponential
growth
Logistic growth
dN
dt 1.0N
1,500 N1,500
K 1,500
0 5 10 150
500
1,000
1,500
2,000
Number of generations
Pop
ulat
ion
size
(N
)
dNdt
(K N)Krmax N
800
600
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0
Time (days)
0 5 10 15
(a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment.
1,000
Nu
mb
er
of
Pa
ram
eci
um
/ml
The Logistic Model and Real Populations
• The growth of laboratory populations of Paramecium
– Fits an S-shaped curve
Logistic Growth and The Real World
• Some populations overshoot K
– Before settling down to a relatively stable density
180
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0
120
90
60
30
Time (days)
0 16014012080 100604020
Nu
mb
er
of
Da
ph
nia
/50
ml
(b) 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.
What type of feedback loop is this?
Logistic Growth and the Real World
• Some populations
– Fluctuate greatly around K
0
80
60
40
20
1975 1980 1985 1990 1995 2000
Time (years)
Nu
mb
er
of
fem
ale
s
(c) 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.
Natural selection (diverse reproductive strategies)a) Relatively few, large offspring (K selected species)b) Many, small offspring (r selected species)
(r selected species)
(K selected species)
Populations Regulated Biotic and Abiotic Factors
Two general questions we can ask about regulation of population growth
1. What environmental factors stop a population from growing?
2. Why do some populations show radical fluctuations in size over time, while others remain stable?
Competition for Resources
• In crowded populations, increasing population density
– Intensifies intraspecific competition for resources
100 100
100
0
1,000
10,000
Ave
rag
e n
um
be
r o
f se
ed
s p
er
rep
rod
uci
ng
ind
ivid
ua
l (lo
g s
cale
)
Ave
rag
e c
lutc
h s
ize
Seeds planted per m2 Density of females
0 7010 20 30 40 50 60 802.8
3.0
3.2
3.4
3.6
3.8
4.0
(a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases.
(b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.
• Many vertebrates and some invertebrates are territorial– Territoriality may limit density
Territoriality: Ocean birds
– Exhibit territoriality in nesting behavior
Health
Population density-Can influence the health and survival of organisms
In dense populations, pathogens can spread more rapidly
Fluctuations in Population Size• Extreme fluctuations in population size
– Are typically more common in invertebrates than in large mammals
Figure 52.19
1950 1960 1970 1980Year
1990
10,000
100,000
730,000C
omm
erci
al c
atch
(kg
) of
m
ale
crab
s (l
og s
cale
)
Population Cycles• Many populations undergo regular boom-and-bust
cycles
Year1850 1875 1900 1925
0
40
80
120
160
0
3
6
9
Lynx
pop
ulat
ion
siz
e (t
hous
and
s)
Har
e po
pula
tion
size
(t
hous
and
s)
Lynx
Snowshoe hare
• Influenced by complex interactions between biotic and abiotic factors
Human Populations• No population can grow indefinitely and humans are no
exception
Figure 52.22
8000 B.C.
4000 B.C.
3000 B.C.
2000 B.C.
1000 B.C.
1000 A.D.
0
The Plague
Hum
an
pop
ulat
ion
(bill
ions
)
2000 A.D.
0
1
2
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6
Global Carrying Capacity
• Just how many humans can the biosphere support?
• Carrying capacity of earth is unknown….
http://www.youtube.com/watch?v=UUOEcNomakw&feature=rec-LGOUT-exp_fresh+div-1r-8-HMhttp://www.youtube.com/watch?v=4B2xOvKFFz4&feature=related
http://www.youtube.com/watch?v=9_9SutNmfFk
• Age structure is commonly represented in pyramids
Figure 52.25
Rapid growth Afghanistan
Slow growth United States
Decrease Italy
Male Female Male Female Male FemaleAge Age
8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8Percent of population Percent of population Percent of population
80–8485
75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34
20–2425–29
10–145–90–4
15–19
80–8485
75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34
20–2425–29
10–145–90–4
15–19
Infant Mortality and Life Expectancy
• Infant mortality and life expectancy at birth
– Vary widely among developed and developing countries but do not capture the wide range of the human condition
Figure 52.26
Developed countries
Developing countries
Developed countries
Developing countries
Infa
nt
mo
rta
lity
(de
ath
s p
er
1,0
00
birt
hs)
Life
exp
ect
an
cy (
yea
rs)
60
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0
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Search for the Missing Sea Otters
Case Study in Population & Community Ecology
Sea OttersEnhydra lutris
Otter Behavior
http://www.youtube.com/watch?v=YQXKyTWMvpM
http://www.youtube.com/watch?v=dQ2Lrnr0gLc
Population Distribution
GROUP QUESTION: 1) What is happening to sea otter populations at several locations in the Aleutian Islands, Alaska? 2) What factors could be contributing to such a rapid change in the size of sea otter populations? Create a list of possible factors.
Group Question: Read above and eliminate some of the reasons for changes in the relative abundance of sea otters at several locations in the Aleutian Islands, Alaska? What does it have to be?
Could the otters simply have migrated from one part of the region to another? To find out, the researchers analyzed populations over a 500-mile-long stretch of the Aleutians from Kiska to Seguam …. By 1993 otter numbers in that whole stretch had been cut by half. Here the geographical scope of the research effort became critical; a smaller region would not have been large enough to reveal the decline. In 1997, they … found that the population decline had worsened, to about 90 percent ….“That told us for sure it was a very large-scale decline, but we were still trying to understand the cause,” Dr. Estes said …. The researchers … ruled out reproductive failure. Their studies enabled them to keep track of how often otters gave birth and how many young survived, and this revealed that reproduction was continuing to re-supply the population.With other possible causes eliminated, … mortality had to be the explanation. In the past, they had seen temporary declines in otter populations because of starvation, pollution or infectious disease. “In all those cases,” Dr. Estes said, “we find lots of bodies. They get weak and tired and come ashore to die.” This time not a single dead otter was found—a clue, he said, that “something really weird was going on.”
(Excerpted from Stevens, William K. “Search for missing sea otters turns up a few surprises.” New York Times, January 5, 1999.)
Orca or Killer WhaleOrcinus orca
Male vs. Female
Orca prey
Orca predation behavior
http://www.youtube.com/watch?v=Ks40worW_gQ (hunting sea lions)
Orcas & learned hunting behavior? (great white sharks??) :http://www.youtube.com/watch?v=SS6NjdGLVZs&feature=related
https://www.youtube.com/watch?v=ypNg19etJg0
1.Make a list of the types of information about killer whales you believe the scientists might need to test their hypothesis that increased predation by the whales was the cause of the sea otter decline.
2.Describe two experiments that would allow you to test the hypothesis that increased predation by killer whales was the cause of the sea otter decline. Keep in mind the following key components of any good experiment: a control (something to which to compare the treatment), replication (do it more than once), and consideration of confounding factors (what might cause differences other than what you manipulate in your experiment?).
Group Questions
Group question: Interpret the two figures. What do they show? How does this provide evidence that orcas were responsible for the decline in sea otters in Kuluk Bay?
Group question: Why do you think Orcas started eating Sea Otters? Generate a list of possible ideas.
Why did Orcas start eating Sea Otters?
• Fish community of the Bering Sea:– Past:– Ocean perch & herring– High abundance– Very high oil content
Why did Orcas start eating Sea Otters?
• Fish community of the Bering Sea:• Present:
– Pollock – High abundance– Low oil content
Why this change in species composition?
• Where did the herring & perch go???
What were Orcas eating before?
Stellar Sea Lions on Amak Island
Harbor Seals
Population decline
Why care about Sea Otters??
• Habitat:
Giant Kelp Forest
Biodiversity
Sea urchins (Echinoderms)