Transcript Nerve activates contraction

CHP. 52 - POPULATIONS
Introduction
Population: group of individuals of a single
species in an area.
SIZE
DENSITY
DISPERSION
SIZE Vs DENSITY
Size = # of individuals in an area
Density = # of individuals
area
Size =4
Density = 4/sq.inch
Measuring density:
Mark-recapture method.
Fig. 52.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Mark-recapture method.
Satellite Tracking
Mark-recapture method.: a
way to estimate population size
10 crocodiles captured & marked
5 captured in next attempt;
Out of 5, 2 marked or recaptured
# Captured = # Marked/ recaptured
Total (N)
Total recaptured
TOTAL (N) = (10 X 5) = 25
2
3) Dispersion = pattern of
spacing
Patterns of dispersion
-Depends on resource/food
distribution, mating opportunities,
predator avoidance, strong
attractions/repulsions
Clumped dispersion - individuals aggregate
in patches - MOST COMMON (why?)
Protection, gathering food (swarms),
‘housing” may be limited (pill bugs), mating,
Fig. 52.2a
Uniform dispersion - individuals are evenly
spaced - not as common
-very territorial species - ‘me casa ‘not your’
casa!’
Fig. 52.2b
Random dispersion - the position of each
individual is independent of the others.
Very rare - like the dandelions in your
yard - depends on where the seed landed
Fig. 52.2c
Recap: What factors can change pop.
Size/density?
1)Birth rate
2)Death rate
3)Immigration - into
4)Emigration - out of
5)Survivorship - how long you live
6)Repoductive output - when you start
makin’ babies ad how many?
(last two together is 7) life history!)
Evolution influences life history (K and r
selection)
What affects population size?
Demography -study of factors that
affect the growth and decline of
populations
1) Birth Rate = # Births/ Time (1/8 sec)
2) Death Rate = #Deaths/Time (1/13 sec)
BIRTH AND DEATH RATES IN USA: FYI
Birth Rate = # Births/ Time (1/8 sec)
Death Rate = #Deaths/Time (1/13 sec)
Per Capita Birth Rate =
# Births/Person ( 13.9 /1000 people)
Per Capita Death Rate =
# Deaths/Person (8.1 /1000 people)
5) Life Table: Age Specific Summary
Of Survival Pattern In A Population
This life table is important to ‘population
size’ and ‘density’ because the longer a
population lives, larger/denser it gets
Table 52.1
(humans)
Copyright © 2002
Pearson Education, Inc., publishing as Benjamin Cummings
5) Life Table - *Cohort (grp of
individuals of the same age)
x-Age
nx
dx
0
1000
200
1.00
2.7
1
800
100
0.80
2.25
2
700
200
0.70
1.50
3
500
300
0.50
0.90
Deaths
4
200
200
0.20
0.50
5
0
0
0.00
--
ex = Life
TOTAL 1000 1000
Ix
ex
x=Age
Category
nx = # living
dx = # of
Expectancy
2.7
Ix=Survivorship – Proportion of offspring
that survive to a particular age
Years in retirement
How long can you expect to
live past your retirement?
ex = Life
Expectancy – How
long a Person Can
Expect To Live
Your Current Age
5) Life Table - *Cohort (grp of
individuals of the same age)
x-Age
nx
dx
0
1000
200
1.00
2.7
1
800
100
0.80
2.25
2
700
200
0.70
1.50
3
500
300
0.50
0.90
Deaths
4
200
200
0.20
0.50
5
0
0
0.00
--
ex = Life
1000
2.7
TOTAL
Ix
ex
x=Age
Category
nx = # living
dx = # of
Expectancy
Ix=Survivorship – Proportion of offspring
that survive to a particular age
5)Survivorship Curve (these are
drawn based on life tables)
1000
100
nx = #
living
10
20
40
60
% of
nx
life
lived
0% 1000
20% 800
30% 700
50% 500
80% 200
80 100
100%
0
Survivorship (%)
5) X axis shows how much life is left to live
•A Type I curve shows a low death rate early in life (humans)
with most individuals living upto old age. (few babies
compared to type 3)
•The Type II curve shows constant mortality (squirrels).
•Type III curve shows a high death rate early in life (oysters).
Species lay a LOT of eggs in this type….why?
6) Okay so apart from how long population lives,
how many babies they make affects population
size/densiy:
Reproductive table: age-specific
summary of the reproductive output in a population.
6) Reproductive table – age specific
summary of reproductive rates in a
mx = average # of
population
offspring produced
x
0
nx
Ix
1000 1.00
mx
Ix mx
0.0
0.0
1
800
0.80
0.5
0.4
2
700
0.70
0.8
0.56
3
500
0.50
0.9
0.45
4
200
0.20
0.0
0.0
5
0
0.00
0.0
0.0
7) Life History: when you can start making babies, how
many babies your population usually makes, when do you
typically DIE (Survivorship)!
All of these affect pop. Size/density!
•2 types: BIG BANG - invest in one massive
reproductive effort - huge number of seeds/eggs once
in many years (Semelparity); why?
Big Bang
/Semelparity –
once - reproduce
Iteroparity –
several
reproductions
7) Life History: when you can start making babies, how
many babies your population usually makes, when do you
typically DIE (Survivorship)!
All of these affect pop. Size/density!
•2 types: Iteroparity- invest in several, regular
reproductive efforts - few seeds/eggs once in a year or
so - more dependable environment/resources
Big Bang
/Semelparity –
once - reproduce
Iteroparity –
several
reproductions
Can you have high reproduction and
survivorship to increase pop. size?
Red deer show a higher mortality rate in
winters following reproductive episodes.
What does this mean?
There is usually a trade off
Fig. 52.5
Recap: What factors can change pop.
Size/density?
Birth rate
Death rate
Immigration - move into an area
Emigration - move out of an area
Survivorship - how long you live
Repoductive output - when you start
makin’ babies ad how many?
(last two together is life history!)
Evolution influences life history (K and r
selection)
Population Growth -what is it?
Population
Growth Rate ‘r’ = Per Capita Birth Rate –
Per Capita Death Rate
Zero population growth rate (r= 0):
Birth rate = Death rate
1) Type: Exponential Population
Growth
Example of exponential
growth
1) Exponential Population Growth
1) Exponential Population Growth
Ideal conditions, LOTS of resources
The number of
individuals in each
generation is a multiple
of the previous
generation
Change
in
number
over
time
dN
dt
 rN
Number of
individuals
Population growth rate
1) Exponential Population Growth
1) Exponential Population Growth
Two stages in Exponential Pop. Growth: First
it starts out slow (why?); then it escalates
rapidly (why?)
Answer: -not enough mating parters in first
case, then as pop. Grows to a critical mass,
there are plaenty of “happy” people!
J Shaped Curve
Density Independent
Population Growth can be
negative!
Example for a population of algae
r=0
r<0
(-)
r>0
(+)
6 offspring in a lifetime - elephants , within 750 years - 19million!
Bacteria - doubling every 20 min. 1 foot of bacteria around the globe in
36 hrs!
2) Logistic Population Growth
•Carrying capacity (K) –
maximum stable population size a
particular environment can support.
2)Logistic Population Growth
S Shaped Curve
Density Dependent
N 


rN
1



•4 phases: a) slow start dt
(same reason Kfrom


dN
before); b) rapid exponential growth (lots of
resources still around…); c)slowing down
(why?); d) population stabilizes - that means
Density Dependent Checks - these are limitations/checks
imposed on growing populations to keep their growth down
1)Intraspecific
Competition:
within one
species
Food is limited
Density Dependent Checks
2)Interspecific
Competition:
competition
between species.
Food and space are
limited. If they are by
themslves, they show
higher pop. growth
Density Dependent Checks
3) Decrease in
Reproductive
Output: less
babies!
Density Dependent Checks
4) Accumulation
of wastes:
living in your
own poop is not
healthy!
Density Dependent Checks
5)Predation:
Boom Bust 10
year cycle –
snowshow hare and
lynx show a
cycling rise and fll
in population that
are correlated
(why?)
Density Dependent Checks
Boccaccio said that the
victims of plague, "ate lunch
with their friend and dinner
with their ancestors in
paradise."
6) Disease:has
to serious
enough to
wipe out
populations or
sections of it:
plague/black
death
2) Logistic Population Growth
•Carrying capacity (K) –
maximum stable population size a
particular environment can support.
Density-dependent factors
increase their affect on a
population as population
density increases.
This is a type of negative
feedback.
Density-independent factors
are unrelated to population
density, and there is no
feedback from the population
Both keep populations at
Fig. 52.13
equilibrium
Density Independent Population
Checks: can act anytime!
Natural Disasters
•drought
•freezes
•hurricane
•floods
•forest fires
K and r selection - based on logistic growth
evolution favors different traits dependng
on how close a popultion is to carrying
capacity
K selection:
Near carrying capacity;
few-but-large-young
r selection:
Low population density;
small-andunprotected young
(close to carrying capacity; r = 0).
K Selection for K strategies: (elephants,
tortoise, endangered species)
1.They mature slowly
2.They have long life spans.
3.They begin breeding later in life.
4.They usually have long generation times.
5.Most produce small numbers of offspring.
6.They take good care of their young (parental
investment)
7. They are usually found in stable habitats
8. Very good at exploiting their minimal
habitat
(far away from carrying capacity; r > 0).
R Selection for R strategies: (mice
(pests), oysters; r is ‘rapid’)
1.They mature rapidly.
2.They have short life spans.
3.They begin breeding early in life.
4.They usually have short generation times
5.They produce large numbers of offspring.
6.They take little care of their offspring, and
infant mortality is huge.
7.They have efficient means of dispersal to new
habitats.
8. They are usually found in disturbed and/or
transitory habitats
DEMOGRAPHIC TRANSITION has 5 stages
•The movement from the first toward the second
Human
Population
state
is called the
demographic transition. Age
structure changes simultaneously
•Zero population
growth = high
birth rates – high
death rates.
•Zero population
growth = low
birth rates – low
death rates.
Age Structure Defined
Share of people younger than 30 in a
population compared to share of people age
60+
Each country is one of 4 major types of age
structures:
1. Very Young (>67% under 30)
2. Youthful (60-67% under 30)
3. Transitional (45-60% under 30)
4. Mature (<45% under 30)
Very Young Age
Structures
62 countries:
most of subSaharan Africa,
Syria, Iraq,
Afghanistan,
3 countries in
Central America,
Haiti, Laos
High mortality
and fertility
rates (stage 2)
Youthful Age Structures
27 countries:
Bangladesh,
Bolivia, Jordan,
Morocco, Nepal,
Peru, Philippines,
Saudi Arabia
Fertility rates
declining, but
still above
replacement
level (stage 2)
Transitional Age
Structures
40 countries:
Brazil, China, India,
Israel, Indonesia,
Lebanon, Malaysia,
Mexico, Sri Lanka,
Thailand, Vietnam
Middle of
demographic
transition (stage 3)
Mature Age Structures
47 countries:
Nearly all of
Europe,
Canada, Cuba,
Russia,
South Korea,
Australia, U.S.
Low mortality
and fertility
rates (stages
4/5)
Age Structure and Conflict
80% of all
new
conflicts
occurred in
countries in
which at
least 60% of
the
population
was under
age 30.
Age Structure and
Governance
Nearly 90% of
countries with very
young structures had
autocratic or weakly
democratic
governments.
More than 80% of
countries with
mature age
structures were fully
democratic.
Mexico 1975 - 2005
Very Young
Transitional
73% under 30
59% under 30
World Age Structures
2005
Human Population – Age Structure
•Age structure is the relative number of individuals of each age changes with each stage of demographic transition.
•can reveal a population’s growth trends, future social conditions.