Population%20Ecology

1
Population Ecology

• Chapter 52

2
Study of populations in relation to environment

• Environmental influences on
• population density and distribution
• age structure
• variations in population size

3
Definition of Population

• Group of individuals of a single species living
  in the same general area

4
Density and Dispersion

• Density
• Is the number of individuals per unit area or
  volume
• Dispersion
• Is the pattern of spacing among individuals
  within the boundaries of the population

5
Density A Dynamic Perspective

• Determining the density of natural populations is
  possible, but difficult to accomplish
• In most cases it is impractical or impossible to
  count all individuals in a population
• How do wildlife biologists approximate
  populations?

6
Estimating Wildlife Population Size
Defined Populations
Undefined Populations
7

• Density is the result of a dynamic interaction of
  
• processes that add individuals to a population
  and those that remove individuals from it

• How do these factors
• Contribute to Population Size??
• Births
• Deaths
• Immigration
• Emigration

Figure 52.2
8
Patterns of Dispersion

• Environmental and social factors influence the
  spacing of individuals in a population

9
Clumped Dispersion

• Individuals aggregate in patches
• May be influenced by resource availability and
  behavior

10
Uniform Dispersion

• Individuals are evenly distributed
• May be influenced by social interactions such as
  territoriality

11
Random Dispersion

• Position of each individual is independent of
  other individuals

(c) Random. Dandelions grow from windblown seeds
that land at random and later germinate.
12
Life history traits are products of natural
selection

• Life history traits are evolutionary outcomes
• Reflected in the development, physiology, and
  behavior of an organism

13
Semelparity Big Bang

• Reproduce a single time and die

14
Iteroparity Repeated Reproduction

• Produce offspring repeatedly over time

15
Trade-offs and Life Histories

• Organisms have finite resources

• Which may lead to trade-offs between survival and
  reproduction

RESULTS

• Kestrels
• Produce a few eggs?
• Can invest more into each, ensuring greater
  survival
• Produce many eggs?
• Costly but if all survive, fitness is better

16
More is Better?

• Some plants produce a large number of small seeds
• Ensuring that at least some of them will grow and
  eventually reproduce

17
Fewer is Better?

• Other types of plants produce a moderate number
  of large seeds
• That provide a large store of energy that will
  help seedlings become established

18
Demography

• Study of the vital statistics of a population
• And how they change over time
• Death rates and birth rates
• Zero population growth
• Occurs when the birth rate equals the death rate

19
Exponential Population Growth

• Population increase under idealized conditions
• No limits on growth
• Under these conditions
• The rate of reproduction is at its maximum,
  called the intrinsic rate of increase

20
Example-understanding growth
Question I offer you a job for 1 cent/day and
your pay will double every day. You will be
hired for 30 days. Will you take my job offer?
Answer If you said YES, you will have made 21
million dollars for 30 days of work. How is
this possible?????
21
1ST DAY OF WORK 1 cent pay/day
30TH DAY OF WORK 10.2 million/day
How is this possible?????
22
Exponential Growth Model
Idealized population in an unlimited environment
Very rapid doubling time steep J curve
r?N(b-d)N ?t rinstrinsic rate of growth
23
Exponential Growth in the Real World

• Characteristic of some populations that are
  rebounding

• Cannot be sustained for long in any population

24
Logistic Population Growth

• A more realistic population model
• Limits growth by incorporating carrying capacity

25
Logistic Population Growth

• Carrying capacity (K)
• Is the maximum population size the environment
  can support

• In the logistic population growth model
• The per capita rate of increase declines as
  carrying capacity is reached

26
Logistic Growth Equation

• Includes K, the carrying capacity

27
Logistic Population Growth

• Produces a sigmoid (S-shaped) curve

Figure 52.12
28
The Logistic Model and Real Populations

• The growth of laboratory populations of paramecia
• Fits an S-shaped curve

29
Logistic Growth and The Real World

• Some populations overshoot K
• Before settling down to a relatively stable
  density

30
Logistic Growth and the Real World

• Some populations
• Fluctuate greatly around K

31
The Logistic Model and Life Histories

• Life history traits favored by natural selection
• May vary with population density and
  environmental conditions

32
Life History and Logistic Growth

• K-selection, or density-dependent selection
• Selects for life history traits that are
  sensitive to population density
• Reproduce slowly, small litters
• r-selection, or density-independent selection
• Selects for life history traits that maximize
  reproduction
• Reproduce rapidly, large litters

33
Natural selection (diverse reproductive
strategies) a) Relatively few, large offspring (K
selected species) b) Many, small offspring (r
selected species)
(K selected species)
(r selected species)
34
Human Populations

• No population can grow indefinitely and humans
  are no exception

35
Global Carrying Capacity

• Just how many humans can the biosphere support?
• Carrying capacity of earth is unknown.

http//www.youtube.com/watch?v9_9SutNmfFk
http//www.youtube.com/watch?vUUOEcNomakwfeature
rec-LGOUT-exp_freshdiv-1r-8-HM
http//www.youtube.com/watch?v4B2xOvKFFz4feature
related
36
Populations Regulated Biotic and Abiotic Factors

• Two general questions we can ask about regulation
  of population growth

• What environmental factors stop a population from
  growing?
• 2. Why do some populations show radical
  fluctuations in size over time, while others
  remain stable?

37
Population Change and Population Density

• In density-independent populations
• Birth rate and death rate do not change with
  population density
• In density-dependent populations
• Birth rates fall and death rates rise with
  population density

38
Density-Dependent Population Regulation

• Density-dependent birth and death rates
• Are an example of negative feedback that
  regulates population growth
• Are affected by many different mechanisms

39
Competition for Resources

• In crowded populations, increasing population
  density
• Intensifies intraspecific competition for
  resources

Figure 52.15a,b
40
Territoriality

• In many vertebrates and some invertebrates
• Territoriality may limit density

41
Territoriality Example Cheetas

• Cheetahs are highly territorial
• Using chemical communication to warn other
  cheetahs of their boundaries

42
Territoriality Ocean birds

• Exhibit territoriality in nesting behavior

43
Health

• Population density
• Can influence the health and survival of
  organisms
• In dense populations
• Pathogens can spread more rapidly

44
Predation

• As a prey population builds up
• Predators may feed preferentially on that species

45
Intrinsic Factors

• For some populations
• Intrinsic (physiological) factors appear to
  regulate population size

46
Population Dynamics

• The study of population dynamics
• Focuses on the complex interactions between
  biotic and abiotic factors that cause variation
  in population size

47
Fluctuations in Population Size

• Extreme fluctuations in population size
• Are typically more common in invertebrates than
  in large mammals

48
Metapopulations and Immigration

• Metapopulations
• Groups of populations linked by immigration and
  emigration

49
Immigration- Movement Into a Population

• High levels of immigration combined with higher
  survival can result in greater stability in
  populations

Figure 52.20
50
Population Cycles

• Many populations undergo regular boom-and-bust
  cycles

• Influenced by complex interactions between biotic
  and abiotic factors

51
The Global Human Population

• The human population increased relatively slowly
  until about 1650 and then began to grow
  exponentially

52
Regional Patterns of Population Change

• To maintain population stability
• A regional human population can exist in one of
  two configurations

• Zero population growth High birth rates High
  death rates
• Zero population growth Low birth rates Low
  death rates

53
Age Structure

• One important demographic factor in present and
  future growth trends
• Is a countrys age structure, the relative number
  of individuals at each age

54

• Age structure is commonly represented in pyramids

55
Infant Mortality and Life Expectancy

• Infant mortality and life expectancy at birth
• Vary widely among developed and developing
  countries but do not capture the wide range of
  the human condition