Download Population - Seattle Central College

Environmental Issues & Problems
ENV 150
Guillaume Mauger
Schedule for today: Population
population in ecosystems:
carrying capacity, growth curves, species
human population:
future projections, resource use, pop. control
Review from last week.
Ecology as the engineer’s perspective:
evaluating ecosystem structure and function
• Types of Ecosystems: Biomes
• Evolution / Nat. Selection / Adaptation
• Characteristics of Sustainable Ecosystems:
–
–
–
–
Reliance on Solar
Nutrient cycling
Biodiversity
Population Control
Quickwrite:
Separate page into 2 Columns
1. Service-Learning:
– Name the organization
you will be working
with, and what you will
be doing, OR
– One sentence on what
you want to do, plus:
• one list the organizations
you have already
contacted, and
• another list on those you
are planning to contact
2. Paper Topic:
1-2 sentences each:
– summary of your paper
topic
– Why it is an important
topic/question
– How it relates to your
service learning
Thomas R. Malthus
An Essay on the Principle of Population
(1798, revised 1826)
“It is observed by Dr. [Benjamin] Franklin
that there is no bound to the prolific
nature of plants or animals but what is
made by their crowding and interfering
with each other’s means of
subsistence.”
Thomas R. Malthus
Thomas R. Malthus
An Essay on the Principle of Population
An Essay on the Principle of Population
(1798, revised 1826)
“… among these effects may be reckoned
a very considerable portion of that vice
and misery, and of that unequal
distribution of the bounties of nature…”
Population
Change in
=
Population
(1798, revised 1826)
“The cause to which I allude is the
constant tendency in all animated life to
increase beyond the nourishment
prepared for it.”
Population Growth
( Births + Immigration )
- ( Deaths + Emigration )
Exponential
(“J” curve)
vs.
Logistic
(“S” curve)
Population Growth
Population Growth
NOTE: this is an
example of stable
population growth
Exponential
(“J” curve)
vs.
Population Growth
Q:
Example of “Irruptive” or
Malthusian growth
Logistic
(“S” curve)
What causes some species to
overshoot/crash and other
populations to grow more slowly?
Population Growth
Q:
What causes some species to
overshoot/crash and other
populations to grow more slowly?
… no clear answer, but …
Population and species
characteristics
“opportunists”
r-selected species
Population and species
characteristics
“Competitors”
k-selected species
• Many small offspring (400/yr)
• Little - no parental care of offspring
• Early reproductive age (3-4 mo.)
• Most offspring die before reaching reproductive age
• Pioneer species
• Generalists
• Fewer, larger offspring (2-3 every 2 years)
• High parental care of offspring (born blind)
• Later reproductive age (4-7 yrs old)
• Most offspring survive to reproductive age
• Late successional species
• Specialists
Review
Human Population
• Carrying Capacity • Sustainable Yield • Natural Capital degradation results
from…?
World Population Projections
Human Population
Definitions:
Crude Birth Rate
= number live births per 1,000
people per year
Crude Death Rate
= number of deaths per 1,000
people per year
Source: UN Dept. of Economic and Social Affairs, “World Population to 2300”, 2009
Human Population
Definitions:
Total Fertility Rate
= average number of children each
woman has in her lifetime
Replacement Rate
= number of children a couple must
have to replace themselves
(different for different countries).
Population Pyramids
Male
Female
Expanding Rapidly
Prereproductive ages 0–14
Male
Female
Expanding Slowly
Reproductive ages 15–44
Male
Female
Male
Stable
Postreproductive ages 45–85+
Female
Declining
Demographic transition
Birth rate and death rate
(number per 1,00 per year)
Stage 1
Preindustrial
Stage 2
Transitional
Stage 3
Industrial
World Population Projections
Stage 4
Postindustrial
Question: Are we overpopulated?
Have we exceeded the Earth’s
carrying capacity? Can we provide
an adequate standard of living to
everyone? Was Malthus right?
Birth rate
Death rate
What are specific consequences
or solutions?
Total population
Growth rate over time
Low
Increasing
Very high Decreasing
Low
Zero
Negative
Source: UN Dept. of Economic and Social Affairs, “World Population to 2300”, 2009
Video: NOVA
Video: Hans Rosling
http://www.ted.com/index.php/talks/hans_rosling_shows_the_best
_stats_you_ve_ever_seen.html
World Population Projections
Source: UN Dept. of Economic and Social Affairs, “World Population to 2300”, 2009