Transcript Ch 8 Lecture 10-11 - myersparkenvironmental

Principles of Population Ecology
i. Population Ecology = deals with species
populations in an area and how/why
those numbers fluctuate over time.
– Study how a population responds to its
environment. Competition, predation, disease
– Populations cannot increase indefinitely
– environmental pressures called “limiting factors”
ii. Population Density = # of individuals of a
species /area or volume at a given time
iii. Age Structure: # of males and females at
each age from birth to death.
World Map
… by Population
… by Gross Domestic Product
… by Child Mortality
… by People living with HIV/AIDS
Current World Population
Global population was 6,904,947,450
On March 10, 2011
• The global population grows by:
– Nearly 2.3 persons per seconds
– Nearly 8,343 persons per hour
– Over 200,234 persons per day
– Over 73 million persons per year
THE UNITED STATES POPULATION
According to the U.S. Census Bureau, the resident
population of the United States, projected to 03/14/12
at 14:57 UTC is:
313,181,425
COMPONENT SETTINGS FOR MARCH 2012
One birth every 8 seconds
One death every12 seconds
One international migrant (net) every 46 sec
Net gain of one person every15 sec.
Human Population Dynamics
There are just three sources of change
in population size:
1. Fertility
2. Mortality
"natural decrease" refers to
population decline resulting from
more deaths than births
3. Migration
Net migration is the number of
immigrants minus emigrants
How do Populations Change in Size?
• Birth Rate (b) = # births per 1000 people / year
• Death Rate (d) = # deaths per 1000 people / year
• Growth Rate (r) = natural increase of a population,
( % / year ). Called “natural increase” in human pops.
• Dispersal:
– Immigration (i) = entering a pop.
– Emigration (e) = exiting a pop.
• Example 1:
• Example 2:
Total Population = 10,000
200 Births/year
(20 births/1000 people)
100 Deaths/year
(10 deaths/1000 people)
Total Population = 10,000
100 Births/year
50 Deaths/year
10 Immigrants
100 Emigrants
r=b–d
r = 20/1000 – 10/1000
r = 0.02 – 0.01
r = 1% per year
r=(b–d)+(i–e)
r = (10/1000 – 5/1000) +
(1/1000 – 10/1000)
r = (.01 – .005) + (.001 – .01)
r = -0.004 …or -0.4%
Doubling Time
• Time it takes for a population to double
itself, assuming that the current growth
rate does not change.
DT=70/AGR%
• You may be given the doubling time and
asked to calculate the AGR% (EASY MATH!)
It is all about math man…
WHY DO WE USE 70 FOR
DOUBLING TIME???
World population is growing at a rate of about 1.7%
IF this rate continues, the population will double
in ~ 42 years ( 70/1.7 = 42)
Unabated, such a rate would lead to a point about 2000 years when the mass of
humanity would weigh more, and be larger, than the Earth.
Dip in the growth rate from1959-1960, for
instance, was due to the Great Leap Forward
in China. During that time, both natural
disasters and decreased agricultural output in
the wake of massive social reorganization
caused China's death rate to rise sharply and
its fertility rate to fall by almost half.
AGE STRUCTURE DIAGRAMS
Which histogram you would consider to be:
Declining, Expanding, or Stable
WHY???
Age Structure Diagrams
LARGEST POPULATION
IN PRE-REPRODUCTIVE
PRE-REPRODUCTIVE &
PRE-
REPRODUCTIVE AGE GROUPS
YEARS
ARE NEARLY EQUAL
REPRODUCTIVE
GROUP IS SMALLER
POSITIVE POPULATION
GROWTH MOMENTUM!!
FEWER PEOPLE WILL BE
POP WILL FALL
PARENTS OF THE NEXT
GENERATION
MORE DEVELOPED – 1999 & 2050
LESS DEVELOPED – 1999 & 2050
WORLD - 1999
LEAST DEVELOPED – 1999 & 2050
Source: http://www.un.org/esa/population/publications/aging99/a99cht3.htm
DEVELOPING or
DEVELOPED?
DEVELOPING or
DEVELOPED?
DEVELOPING or
DEVELOPED?
DEVELOPING or
DEVELOPED?
Tracking the baby-boom generation
in the United States
The Power of the Pyramids!
• Put your name on your paper.
• Look at the back of your page…
– Find 2 other students who have DIFFERENT
countries as you.
• You’re making Age-Sex Histograms today.
• Make ‘em colorful and fun! Don’t spend too
much time “prettying it up” – you have
analysis questions to do!
• Calculator time-saver:
– If you’re using a TI-83, store the # you’re
dividing by as a letter. It’ll save tons of time!
Maximum Population Growth
• Biotic Potential or Intrinsic Rate of Increase
– Max. rate at which a pop could increase under
ideal conditions.
• Life History Characteristics affect biotic potential.
– Age at which reproduction begins
– Fraction of life when reproduction is possible
– # reproductive periods per lifetime
– # offspring produced during each reproductive period
•Generally…
– Smaller organisms have high biotic potential.
– Larger organisms have low biotic potential.
10.9
9.3
7.9
World Pop
1800-2100
Based on
UN 2004
Projections
(red, orange,
green)
& US
Census
Bureau
historical
estimates
(black).
EXPONENTIAL GROWTH
ALL organisms show Exponential Growth…
…IF they’re growing at their biotic potential
(time may vary)
J-shaped
curve
EXPONENTIAL
MODEL
Increase or
decrease
competition?
Is crowding a
problem?
YES!
CARRYING CAPACITY “K”
Carrying Capacity (K)= # organisms that the
environment can support over a given time.
• Fluctuates due to environmental changes or limiting
factors! ENVIRONMENTAL RESISTANCE
– abiotic (light, temp, nutrients, weather, etc)
– biotic (food, prey, disease, adaptable, etc)
Forms an
S- shape graph
Limits population growth
Feedback loop… + or – ?
LOGISTIC
MODEL
LOGISTIC Curves:
show fluctuations!
LOGISTIC Curves:
show fluctuations!
S-shaped Curves:
a CRASH could occur!!
WHY would
this happen?
Resources
are
exhausted!
Why is estimating carrying capacity
for an individual country misleading,
based on what you know about
human civilization & resource use?
IMPORTS
TRANSPORTATION
ENVIRONMENT
ALTERATION
IMMIGRATION
EXPORTS
TECHNOLOGY
EXCHANGING
SERVICES
EMIGRATION
MOTHER
NATURE
Reproductive Strategies
r strategists
– Recall: r = growth rate!
– r-selected species have a
high growth rate
– Characteristics:
• Small body size
• Early maturity
• Short life span
• Large broods
• Little or no parental care
• Usually in unpredictable
environments (long-term survival
low)
• Low ability to compete
Mosquitoes & Weeds
K strategists
– Recall: K = carrying cap.
– Maximize survival when
the pop. is near K.
– Characteristics:
• Few offspring
• Long life spans
• Slow reproduction
• Late reproduction
• Parental care
• Large body size
• Usually in stable
environments
Humans, Owls,
Trees,Whales
Survivorship
• Probability that a given individual in a
population will survive to a particular age.
– Type I = prob. of death greatest when old.
– Type III = prob. of death greatest when young.
• If early death is avoided, survival chance is high
– Type II = prob. of death equal through life.
• Death events have little age bias.
THESE ARE
GENERALIZATIONS!!
(few species fit 1 curve)
Survivorship curves change
throughout life for most species.
Factors that Affect Population Size
• Density-Dependent Factors
– Effects of the factor are changed with a changing
population size
– Examples:
• Disease
• Competition for resources (food, space, etc)
• Predator-prey relationships
• Density-Independent Factors
– Effects of the factor are unchanged with a changing
population size
– Examples:
• Typically abiotic factors
• Random weather events
Predator-Prey Curve
Case-in-Point:
Predator-Prey Dynamics
on Isle Royale
• Moose wandered to this island by crossing the frozen Lake
Superior – Population Boomed!
• Wolves wandered there later – Population Boomed!
Moose over K
Moose inc. due to
few predators
Canine
Parvovirus
Moose dec.
due to being
over K –
Lack of Food!
DD or DI?
Wolves inc. due
to more food
Wolf dec. due
to less food
Boom – Or – Bust Cycle
Lemming Population
(1) population is
increasing, and
density-dependent
factors are
increasingly severe.
(2) Population is
declining, and
density-dependent
factors are
increasingly relaxed.
Current Human Population
• Between 2001 and 2002 – World
Population increased by 78M.
– Not due to increased birth rate – it declined!
– It’s due to a decreased death rate!
•Why?
– Better medicine
– Better technology
– Lots of reasons!
Human Population
(1800 – present)
Projecting Future Population
• Population continues to increase
• Growth rate continues to decrease
• Prediction:
– Growth rate will continue to decrease slowly
until zero population growth is attained (b = d)
Mexican
Revolution
b and r
in Mexico
(1900 – 2000)
Types of Fertility Rates that Affect
Human Population Growth
• Total fertility rate (TFR)
–
–
–
–
The average number of children born to a woman
Average in developed countries = 1.5
Average in developing countries = 3.8
Worldwide 1990: 3.1
now: 2.8
• Replacement fertility rate (RFR)
– The number of children a couple must have to
replace themselves
– A RFR of 2.1 for developed countries with low
infant and child mortality rates
– Africa RFR = 2.5
Projecting Future Population
2000 UN Estimates
World
10.9 B
population
will be
9.3 B =
between… “most likely”
7.9 B
Projections
use estimates
of future b, d,
and migration.
This graph is based on
different fertility rates.
2002: 2.8 children/woman
– If it declines to 1.5,
population will be 7.9 B
– If it declines to 2.5,
population will be 10.9 B
small changes make a
BIG difference!
??? What is Earth’s K ???
– 4 B – 16 B??
– Based on standards of living,
resource consumption,
technology, and waste
generation.
Demographics
The applied branch of sociology that deals with
population statistics
HIGHLY DEVELOPED /
DEVELOPED
– Low r, low b
– highly industrialized
– low infant mortality (#
deaths age 0-1 per 1000
live births)
– Longer life expectancy
– High avg. per capita
GNI PPP (amt. goods &
services the average
citizen could buy)
DEVELOPING
– High b, high r
– Less industrialized
overall
– Shorter life expectancy
– Lowest avg. GNI PPP
• Can be moderately
developed or less
developed.
• Moderately developed
is just that… moderate!
Doubling Time &
Replacement-Level Fertility
Doubling Time = amount of time it would take for
the population to double in size.
– Assumes the r won’t change.
td = 70 / r
– Can identify a country as highly, moderately, or less
developed. (Shorter doubling time = less developed)
Replacement-Level Fertility = # children a couple
must produce to “replace” themselves.
– 2.1 children
– It’s not 2.0 because some infants and children die
before reaching reproductive age
– Currently, total fertility rate worldwide = 2.8
Demographic Stages
(1) Preindustrial
(3) Industrial
• High b, d, & infant mortality
• Pop grows slowly or declines slightly
• War, plague, or famine increases d
• Industrialization occurs
• Decline in b, relatively low d
• Population growth rate slows.
(2) Transitional
(4) Postindustrial
• Lowered d, but b remains high
• Population grows rapidly
• Low b and d
• People desire smaller families (better
education, more $$)
• Population grows slowly or not at all
Population and Resource USE