Population and Community Ecology

1
Population and Community Ecology

• Chapter 35

2
Defining Populations

• Populations change over time? decrease or
  increase
• Factors that influence size
• Availability of food and space
• Weather conditions
• Breeding patterns
• To study the effects of these factors ecologists
  define the geographic boundaries of a population

3
Population Density

• The number of individuals of a particular species
  per unit area or volume.
• Is a helpful measurement for comparing
  populations in different locations.
• Population density  Individuals/Unit Area
• Ex 1000 trees in an area of 50Km2
• PD 1000/ 50Km2 20 trees /Km2

4
Sampling Techniques

• Quadrats A particular area is marked off then
  the number of a particular species within this
  boundary is counted.
• Indirect Counting Certain organisms that move
  around a lot or are difficult to see, therefore
  nests, burrows, or tracks are counted rather than
  the organisms themselves.
• Mark-Recapture Organisms are captured, marked
  and then released. Later organisms are captured
  and the marked and unmarked ones are counted

5
Limits to Accuracy

• Quadrat Method? popln distributed evenly? not
  so,if quadrat includes clumps ? s too high,if
  not ? s too low
• Mark-Recapture? captured animals wary of traps,
  avoid traps? size is overestimated

6
Limits to Population Growth

• Section 35.2

7
Exponential Growth of Populations

• Population multiplies by a constant factor at
  constant time intervals.
• One cell becomes 2, every 20 minutes the
  population doubles

8
Carrying Capacity

• The number of organisms in a population that the
  environment can maintain, or carry, with no net
  increase or decrease.
• Limiting Factor a condition that can restrict a
  population's growth.
• Ex Space, disease and availability of food.

9
Factors Affecting Population Growth

• Density-Dependent Factors
• Food, diseases
• Density-Independent Factors
• Extreme weather events, such as hurricanes,
  blizzards, ice storms, and droughts, have the
  same effect on a population regardless of its
  size.
• Population Growth CyclesSome populations have
  "boom-and-bust" growth cycles They increase
  rapidly for a period of time (the "boom"), but
  then rapidly decline in numbers (the "bust").

10
Predicting Human Population Growth

• CH 35.3

11
Age Structure

• The proportion of people in different age groups.
  
• Can predict future trends, and help determine
  the earths carrying capacity

12
Species Interaction

• Ch 35.4

13
Species Interactions
Commensalism
Predation
Parasitism
Competition
Mutualism
14
Competition Between Species

• Interspecies Competition Two or more species
  compete for the same source of food or shelter
• Competitive Exclusion Two similar species,
  having the same requirements, one succeeds over
  the other

15
Predation

• One species hunt and kills another for food
• Both the predator and the prey have adaptations
  that help them either to catch the prey, or to
  avoid being caught.

16
Parasitism

• One organism obtains food at the expense of
  another
• Ex mosquitoes, tapeworms that live and feed in
  the intestines of animals

17
Mutualism

• Both organisms benefit from this relationship

18
Commensalism

• One organism benefit while the other is neither
  benefited nor harmed

19
Disturbances to Communities

• Ch 35.5

20
How Ecosystems Change

• Ecosystems are in a state of continual change
• Populations are slowly replaced by other/new
  populations
• Humans can also cause changes

21
Succession

• A regular pattern of changes in the type of
  species of a community

22
Succession

• Causes
• New community makes it difficult for the old to
  survive
• Ex Pine shade ? pine seedling cant grow? oak,
  maple grow? replace the pine trees

23
Succession

• Climax Community the community that is
  eventually formed if the land is left undisturbed

24
Primary Succession

• Succession that occurs on surfaces where no
  ecosystem existed
• Ex New Islands, glaciers retreats, cracks in
  rocks

25
Secondary Succession

• Succession that occurs on a surface where an
  ecosystem had previously existed.

26
Secondary Succession

• Pioneers
• The first organism to colonize a newly available
  area and start the process of succession

27
Secondary Succession
28
Human Activities and Species Diversity

• Clearing Land? farming, building, urbanization?
  loss of species
• Introduced Species

29
Exotic Species

• Species not native to an area
• Native species have no natural defense against
  them