populations and their size definition of a population: all ... · population change population...
TRANSCRIPT
Ecologists
work at
many
scales
Ecologists
work at
many
scales
Populations
Populations
• Groups of organisms of
the same species that live
within a given area
Po
pu
latio
n C
ha
racte
ristics
We can characterize individual
populations in terms of …
Variation
Patterns of Dispersion
Demographics
Size and Density
Limits on population growth
Human population growth
• Members of a population show similarities
because they belong to the same species.
Members of a population also show variation.
Most variation falls in a “normal” distribution (bell-shaped frequency).
Po
pu
latio
n C
ha
racte
ristics
We can characterize individual
populations in terms of …
Variation
Patterns of Dispersion
Demographics
Size and Density
Limits on population growth
Human population growth
There are three common patterns of
population distribution:
Uniform
Po
pu
latio
n C
ha
racte
ristics
We can characterize individual
populations in terms of …
Variation
Patterns of Dispersion
Demographics
Size and Density
Limits on population growth
Human population growth
Demographics
• Characteristics of a population
• Examples:
– Average age
– Average size
– Average number of offspring
• http://quickfacts.census.gov/qfd/states/53000.html
Po
pu
latio
n C
ha
racte
ristics
We can characterize individual
populations in terms of …
Variation
Patterns of Dispersion
Demographics
Size and Density
Limits on population growth
Human population growth
Four Factors Influence the
Size of a Population:
• Natality: Birth Rate (offspring
produced and added to population)
Mortality: Death Rate
(individuals that die)
• Immigration: Movement of members of the
species into the area
• Emigration: Movement of members of the
species out of area to live elsewhere.
Population Change
Population Change =
(natality + immigration) –
(mortality + emigration)
Exponential Curve
Unlimited Growth
(J-Shaped)
Populations tend to
grow in size for the
simple reason that
individuals tend to
have more than one
offspring.
Can this happen in nature?
• Yes: Bacteria
–If there are no
factors limiting
the growth, their
number will
increase rapidly.
Exponential growth of bacteria
Can this happen in nature?
• Yes: Invasive species
– Uniform habitat
– No predators
– No disease
– Unlimited area
– Abundant food
• Pythons
Logistic Curve
Limited Growth (S-Shaped)
3 Phases:
1. Exponential growth Phase
2. Transitional Phase
3. Plateau Phase
Exponential Growth Phase
• Population increases
exponentially.
• Resources are abundant.
• Predators and disease are
rare.
Transitional Phase
• As a result of intra-specific
competition
– for food, shelter, nesting
space, etc.,
– and the build up of waste.
• The growth rate slows
down.
– Birth rates decline and
death rate increases
Plateau Phase
• Natality and mortality are equal so population size is
constant.
• When the number of individuals in the population
have reached the maximum which can be supported
by the environment.
The number is called the
CARRYING CAPACITY
Growth of a population of fur seals
Population size oscillates around
the carrying capacity (K)
Time
N
K
overshoot
oscillations
Po
pu
latio
n C
ha
racte
ristics
We can characterize individual
populations in terms of …
Variation
Patterns of Dispersion
Demographics
Size and Density
Limits on population growth
Human population growth
Limits on Population Growth
• Density Dependent Limits
– Food
– Water
– Shelter
– Disease
• Density Independent Limits
– Natural Disasters
– Humans (logging, mining, farming)
Water and shelter are
critical limiting factors in
the desert.
Fire is an example of a
Density independent
Limiting factor.
Po
pu
latio
n C
ha
racte
ristics
We can characterize individual
populations in terms of …
Variation
Patterns of Dispersion
Demographics
Size and Density
Limits on population growth
Human population growth
World Population Events
Time unit Births Deaths Growth
-------------------------------------------------
Year 131,571,719 55,001,289 76,570,430
Month 10,964,310 4,583,441 6,380,869
Day 360,470 150,688 209,782
Hour 15,020 6,279 8,741
Minute 250 105 146
Second 4.2 1.7 2.4
-------------------------------------------------
What’s Behind Population Growth
• Three Factors
– Fertility
– Infant Mortality
– Longevity
• Animal Domestication
and Agriculture
– Provided for a few to
feed many
• Industrial Revolution
– Growth of Cities and
Infrastructure
• Water
• Energy
• Transportation
– Increased Productivity
– Nutrition
– Sanitation
– Medicine
Age structures of three nations
Are these growing, shrinking or stable populations?
Shrinking Growing Stable
Exponential growth of the human population
Human population growth
does not currently show
density effects that typically
characterize natural populations.
Limited resources eventually will
cause human population
growth to slow,
but global human
carrying capacity is not known.
Population Predictions
• Most
predictions:
9-12B by 2050
10-15B by 2100
• Large
uncertainties
Resource Limits
• Land
– Deforesting to acquire more arable land
– Would run out in next century at current yields
• Water
– In 1950 people used half of accessible water
– Are now dependent on dams
– Pollution loses 33% of potential water
– Getting close to limits
• Energy
– growth very high last fifty years
– Mostly hydrocarbon fuels
– Nonrenewable resource consumption
– Climate change issues
Question:
Why are humans
destroying the earth?
destructamundo
destructamundo
destructamundo
destructamundo
Question:
Why do locusts destroy crops?
nymph aggregating nymphs adults feeding
swarming destrutamundo
Limits: Locust Freedom Without Responsibility
= Destroyed Crops (destruction of environment)
It’s a
free country!
I’ve got my rights!
Who’s going to stop me?
Question:
Why do some microbes make us sick?
©Phage et al.
Limits: Pathogen Freedom Without Responsibility
= Disease! (destruction of the body environment)
It’s a free country Who’s going
to stop me?
I’ve got my rights!
Bacterial
pathogens
Question:
Why are humans
destroying the earth?
destructamundo
destructamundo
destructamundo
destructamundo
Human Freedom Without Responsibility
= Destructamundo! (destruction of environment)
It’s a free country
Who’s going to stop me?
I’ve got my rights!
urban sprawl
global warming
deforestation
desertification overpopulation
air polution
water polution
loss of
habitat
overconsumption
conspicuous consumption
loss of farmland
overfishing
greenhouse effect
ozone hole
mass extinction
greed
loss of wetlands
NIMBY = “not in my
backyard”
lack of cooperation
out-of-control
materialism
lack of cooperation special interests
destruction TEOTWAWKI = “the end of the world as we know it”
radical anti-environmentalism
might makes right
short-term thinking
fish kills
toxic algal
blooms
erosion
loss of topsoil
bigger is better monoculture
pesticides
the bottom line
Humans need to be better ecologists.