Population Ecology Part 2 Discussion population ecosystem community biosphere organism.
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Transcript of Population Ecology Part 2 Discussion population ecosystem community biosphere organism.
![Page 1: Population Ecology Part 2 Discussion population ecosystem community biosphere organism.](https://reader031.fdocuments.us/reader031/viewer/2022032607/56649ebb5503460f94bc354f/html5/thumbnails/1.jpg)
Population EcologyPart 2
Discussion
population
ecosystem
community
biosphere
organism
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Big Questions:
• What characterizes a population?• What important factors influence population
growth?
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Population Size• Changes to
population size– adding & removing
individuals from a population
• birth• death• immigration• emigration
Births and immigration add individuals to a population.
Births Immigration
PopuIationsize
Emigration
Deaths
Deaths and emigration remove individuals from
a population.
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Population growth rates• Factors affecting population growth rate
– sex ratio• how many females vs. males?
– generation time• at what age do females reproduce?
– age structure• how females at reproductive age in cohort?
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Life table
Demography• Factors that affect growth & decline of
populations– vital statistics & how they change over time
Why do teenage boys pay high car insurance rates?
females males
What adaptations have led to this difference
in male vs. femalemortality?
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Survivorship curves• Graphic representation of life table
Belding ground squirrel
The relatively straight lines of the plots indicate relatively constant rates of death; however, males have a lower survival rate overall than females.
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Age structure• Relative number of individuals of each age
What do these data imply about population growth in these countries?
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Survivorship curves
• Generalized strategiesWhat do these graphs tell about survival & strategy of a species?
0 25
1000
100
Human(type I)
Hydra(type II)
Oyster(type III)
10
150
Percent of maximum life span
10075
Su
rviv
al p
er th
ousa
nd
I. High death rate in post-reproductive years
II. Constant mortality rate throughout life span
III. Very high early mortality but the few survivors then live long (stay reproductive)
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Trade-offs: survival vs. reproduction• The cost of reproduction
– increase reproduction may decrease survival• age at first reproduction • investment per offspring• number of reproductive cycles per lifetime
Natural selection favors a life history that maximizes lifetime reproductive success
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Reproductive strategies• K-selected
– late reproduction– few offspring– invest a lot in raising offspring
• primates• coconut
• r-selected– early reproduction– many offspring– little parental care
• insects• many plants
K-selected
r-selected
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Trade offsNumber & size of offspring
vs.Survival of offspring or parent
r-selected
K-selected
“Of course, long before you mature, most of you will be eaten.”
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Life strategies & survivorship curves
0 25
1000
100
Human(type I)
Hydra(type II)
Oyster(type III)
10
1
50
Percent of maximum life span
10075
Su
rviv
al p
er th
ousa
ndK-selection
r-selection
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Population growthchange in population = births – deathsExponential model (ideal conditions)
dN = riNdt
N = # of individualsr = rate of growthri = intrinsic ratet = timed = rate of change
growth increasing at constant rate
intrinsic rate = maximum rate of growth
every pair has 4 offspring
every pair has 3 offspring
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Exponential growth rate• Characteristic of populations without
limiting factors – introduced to a new environment or rebounding from a
catastrophe
African elephantprotected from hunting
Whooping cranecoming back from near extinction
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K =carryingcapacity
Logistic rate of growth• Can populations continue to grow
exponentially? Of course not!
effect of natural controls
no natural controls
What happens as N approaches K?
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Influence of population size (N) on per capita rate of increase (r)
Maximum
Positive
Negative
0N K
Population size (N)
Per
cap
ita r
ate
of in
crea
se (r)
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Population growth predicted by the logistic model
dNdt
1.0N Exponential growth
Logistic growth
dNdt
1.0N1,500 N
1,500
K 1,500
0 5 10 150
500
1,000
1,500
2,000
Number of generations
Pop
ulat
ion
size
(N
)
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500
400
300
200
100
0200 10 30 5040 60
Time (days)
Num
ber
of
clad
ocer
ans
(per
20
0 m
l)
• Maximum population size that environment can support with no degradation of habitat– varies with
changes in resources
Time (years)1915 1925 1935 1945
10
8
6
4
2
0Num
ber
of
bre
edin
g m
ale
fur
se
als
(tho
usa
nds)
Carrying capacity
What’s going on with the plankton?
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Changes in Carrying Capacity
• Population cycles– predator – prey
interactions
At what population level is the
carrying capacity?
K
K
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2007-2008
AnyQuestions?
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• What influences populations to adopt r or k life history strategies?
• Explain exponential growth.• Know what carrying capacity is.• Explain why human populations are
experiencing exponential growth.