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Population and Community Ecology

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Commensalism. Competition Between Species ... Commensalism. One organism benefit while the other is neither benefited nor harmed ... – PowerPoint PPT presentation

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Title: 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
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