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Population Dynamics Day 4

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Population Dynamics Day 4 Break here What population do you think this is? So, what do you think is going to happen to the human population? We will probably reach ... – PowerPoint PPT presentation

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Date added: 6 July 2019
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Title: Population Dynamics Day 4


1
Population DynamicsDay 4
2
Population Characteristics
  • Population Density
  • The number of organisms per unit area
  • Dispersion
  • The pattern of spacing a population within an
    area
  • 3 main types of dispersion
  • Clumped
  • Uniform
  • Random
  • Resource availability determines dispersion
    patterns

3
Population Limiting Factors
  • 1) Density-independent factors
  • Factors that limit population size, regardless of
    population density.
  • usually abiotic
  • include natural phenomena
  • Ex. drought, flood, fire extreme temperature,
    tornadoes, etc.

4
Population Limiting Factors (cont.)
  • 2) Density-dependent factors
  • Any environmental factor that depends on the
    density of the population
  • Usually biotic
  • For ex.
  • Predation
  • Disease
  • Parasites
  • Competition

5
Population Limiting Factors (cont.)
  • 3) Population growth rate
  • How fast a population grows
  • Factors that influence this are
  • Natality (____ rate)
  • Mortality (_____ rate)
  • Emigration (the number of individuals moving
    _________ a population)
  • Immigration (the number of individuals _________
    a population)

birth
death
away from
moving to
6
Break here
7
Understanding Exponentials
  • Put your pens down for a minute think about
    this
  • An employer offers you two equal jobs for one
    hour each day for fourteen days.
  • The first pays 10 an hour.
  • The second pays only 1 cent a hour, but the rate
    doubles each hour.
  • Which job will you accept?

8
Understanding Exponentials
Now, how much would your employer owe you if you
stayed at this job for another 2 weeks?
Job 2 lags for a long time before exponential
growth kicks in!
What would happen if this type of growth took
place within a population?
9
Population Growth Models
  • 1) Exponential growth model
  • Also called geometric growth or J-shaped growth.
  • First growth phase is slow and called the lag
    phase
  • Second growth phase is rapid and called the
    exponential growth phase
  • Bacteria can grow at this rate, so why arent we
    up to our ears in bacterial cells?

10
Population Growth Models (cont.)
  • Limits to exponential growth
  • As population density increases, competition
    follows as nutrients and resources are used up
  • The limit to population size that a particular
    environment can support is called carrying
    capacity (k)
  • When youre done writing, put your pens down

11
What population do you think this is?
12
So, what do you think is going to happen to the
human population?
  • We will probably reach our carrying capacity.
  • Our growth rate will start to look like most
    organisms, which is the Logistic Growth Model

Carrying Capacity (k)
What letter does this curve kind of look like?
13
Population Growth Models (cont.)
  • 2) Logistical growth model
  • Often called the S-shaped growth curve
  • Growth slows or stops following exponential
    growth at the populations carrying capacity
  • Populations stop increasing when
  • Birth rate lt Death rate
  • Emigration gt Immigration
  • Carrying capacity can be raised or lowered. How?
  • Ex. 1 Artificial fertilizers have raised
  • Ex. 2 Decreased habitat can lower k

14
Community Dynamics
  • Day 5

15
Communities
  • Review
  • A community is a group of interacting populations
    that occupy the same area at the same time.

16
Limiting Factors of Communities
  • Any abiotic or biotic factor that restricts the
    numbers, reproduction, or distribution of
    organisms.

17
Range of Tolerance
  • Upper and lower limit of conditions in which an
    organism can survive.
  • Ex. Temperature, Salinity, pH

18
Ecological Succession
  • The change in an ecosystem that happens when one
    community replaces another as a result of
    changing biotic and abiotic factors

19
Ecological Succession (cont.)
  • 2 types
  • 10 Primary Succession
  • 20 Secondary Succession

20
Primary Succession
  • In primary succession (10), the community
    establishes in an area of exposed rock (no soil)
  • It occurs very slowly at first

21
Primary Succession (cont.)
  • Pioneer species, or the first organisms to
    arrive, are usually lichens or mosses
  • They secrete acids that can break down rock,
    creating soil.

22
Primary Succession (cont.)
  • Small weedy plants and other organisms become
    established.
  • As they die, more soil is made

23
Primary Succession (cont.)
  • Animals, water and wind bring seeds that sprout
  • Eventually there is enough soil for shrubs and
    trees to grow.

24
Primary Succession (cont.)
  • The stable, mature community that eventually
    develops from bare rock is called a climax
    community.

25
Secondary (20) Succession
  • Disturbances (fire, flood, windstorms) can
    disrupt a community.
  • After a disturbance, new species of plants and
    animals might occupy the habitat.

26
Secondary Succession (cont.)
  • Pioneer species in 20 succession are usually
    plants that grow in disturbed area.
  • Much fasterthan 10succession

27
Succession End point?
  • Cannot be predicted
  • Different rates of growth human
    involvementmake it impossible toknow if a true
    climaxcommunity has beenreached.
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