POPULATIONS

1
POPULATIONS

• Growth
• Limitations
• Human Population

2
Stable Populations

• Stable ecosystems are established by keystone
  species.
• Keystone species are the population of organisms
  that keep the ecosystem in balance without this
  population the ecosystem would disappear.
• Sea otters are a keystone species in the kelp
  forest aquatic ecosystem.
• Sea otters eat sea urchins sea urchins eat kelp.
  If the sea urchins grew too large numbers then
  they would completely destroy the kelp forest
  which is home to hundreds of other animals. If
  the sea otter disappears then the kelp forest
  will be destroyed.

3
Characteristics of all Populations

1. Geographic distribution- Where?
2. Density- How many per unit of area?
3. Growth Rate- How fast do they reproduce and grow?
4. Population Age Structure- How old are the
   individuals in the population?

4
Density (Population Spacing)

• Dispersal patterns within a population

Provides insight into the environmental
associations social interactions of
individuals in population
clumped
random
uniform
5
Population Growth

• Factors that affect size
• Number of births
• Number of deaths
• Number of individuals that enter or leave the
  population (immigration, emigration)

6
How fast can a population grow?

• Populations usually stay about the same size from
  year to year because various factors kill many
  individuals before they can reproduce.
• Predation
• Disease
• Natural disasters
• Competition

7
Exponential Growth

• Population grows fast
• When graphed it forms a J-shaped curve
• Occurs in nature under conditions where plenty of
  food, water and space are available and there is
  minimal competition and predation

8
Logistic Growth

• Population growth slows or stops after
  exponential growth
• Population growth slows when it reaches carrying
  capacity
• Carrying capacity (K) is determined by limited
  resources

9
Resources have limits

• Resource limits A species reaches its carrying
  capacity when it consumes a resource at the same
  rate that the resource is produced. This
  resource is then called the limiting factor for
  the species.

10
Limiting Factors

• DENSITY DEPENDENT death occurs more quickly in
  crowded populations rather than in a sparse
  population. Limited resources, predation, and
  disease often result in higher death rates in a
  high density population

• DENSITY INDEPENDENT a certain proportion of a
  population dies regardless of the density. This
  affects all members of a population in a uniform
  way. Severe weather and natural disasters are
  often density independent causes of death

11
Methods for measuring population size

• Random Sampling- rather than count all
  individuals in an area a grip can be used to
  identify the number per unit of area and then
  multiplied to the complete area

• Capture and Release-each captured organism is
  tagged and released. Then a recapture is done
  and the population size can be estimated by
  comparing the number captured that are tagged vs
  not tagged.

12
The Human Population

• The human population grew more in 20th century
  than ever before (Exponential growth)
• Why?
• Increased food production
• Improved hygiene with industrial and scientific
  revolutions
• Can it continue?

13
Human Population Growth
14
Demography

• 2 Categories
• Developed Countries have higher average incomes,
  slower population growth, and diverse industrial
  economics
• Developing Countries lower average incomes,
  simple and agricultural based economics, and
  rapid population growth.

15
Distribution of population growth
11
uneven distribution of population 90 of births
are in developing countries
10
high fertility
9
uneven distribution of resources wealthiest 20
consumes 90 of resourcesincreasing gap between
rich poor
medium fertility
8
7
low fertility
6
World total
World population in billions
5
4
Developing countries
3
2
1
Developed countries
0
1950
1900
2000
2050
Time
16
Age structure Diagram

• Relative number of individuals of each age

What do these data imply about population growth
in these countries?
17
Women and Fertility

• What leads to decreases in birth rates?
• Increased education
• Economic independence for women
• Large families are valuable in communities in
  which children work or take care of older family
  members
• Movement of people seeing children as a financial
  burden rather than an asset
• Fertility rate
• Developed countries 1.6 children/woman
• Developing countries 3.1 children/woman