Population Ecology Chapter 52 U110PP - PowerPoint PPT Presentation

Title: Population Ecology Chapter 52 U110PP


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Population Ecology- Chapter 52 U110PP
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Demography

• Demography is the study of the vital statistics
  of a population
• And how they change over time
• Death rates and birth rates
• Are of particular interest to demographers

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Life Tables

• A life table
• Is an age-specific summary of the survival
  pattern of a population
• Is best constructed by following the fate of a
  cohort (a group of the same age group)
• Every cohort has a characteristic fecundity and
  mortality

Life tables provide a lot of predictive power
about a population
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• The life table of Beldings ground squirrels
• Reveals many things about this population

1. Females live longer
2. Death rate relatively constant
Table 52.1
Not easy to produce life tables- precise tracking
required
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Survivorship Curves

• A survivorship curve
• Is a graphic way of representing the data in a
  life table

Want to buy life insurance?
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• The survivorship curve for Beldings ground
  squirrels
• Shows that the death rate is relatively constant

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• Survivorship curves can be classified into three
  general types
• Type I, Type II, and Type III

Late loss
Constant loss
Early loss
Figure 52.5
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Reproductive Rates

• A reproductive table, or fertility schedule
• Is an age-specific summary of the reproductive
  rates in a population
• When in the population do individuals reproduce
  and how many offspring do they produce?

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• A reproductive table
• Describes the reproductive patterns of a
  population

Who makes babies and when amd how many
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• Concept 52.2 Life history traits are products of
  natural selection
• Life history traits are evolutionary outcomes
• Life history traits or characteristics that aid
  in survival and reproduction
• Reflected in the development, physiology, and
  behavior of an organism

Think of this as the evolutionary choices
populations have made
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Life History Diversity

• Life histories are very diverse
• Clutch size?
• Trade off between number and size
• Reproductive events per lifetime?
• Trade off between fewer, big events and many,
  smaller events
• Age at first reproduction?
• Trade off between early reproduction (low
  survival) and later reproduction (higher
  survival)
• Parental care?
• Trade off between investing resources in fewer
  offspring and not investing in lots of offspring

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Trade-offs and Life Histories

• Organisms have finite resources

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

RESULTS
resources
reproduction
survival
Figure 52.7
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• Some species that exhibit semelparity, or
  big-bang reproduction
• Reproduce a single time and die

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• Some species that exhibit iteroparity, or
  repeated reproduction
• Produce offspring repeatedly over time

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

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

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Wait. If you are saying that there is a
trade-off between survival and reproduction,
wouldnt reproductive individuals have a higher
mortality?
Yep!
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Recall
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• Concept 52.3 The exponential model describes
  population growth in an idealized, unlimited
  environment
• It is useful to study population growth in an
  idealized situation
• In order to understand the capacity of species
  for increase and the conditions that may
  facilitate this type of growth

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What causes changes in population size?
- Deaths Emigration
Births Immigration

• If immigration and emigration are ignored
• A populations change in size equals births minus
  deaths

For simplicity, we usually consider PER CAPITA
birth rates, death rates, and population growth
rates
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• Zero population growth
• Occurs when the birth rate equals the death rate
• To make this simpler, we usually refer to r (the
  intrinsic rate of growth) as b/N d/N
• The population growth equation can be expressed as

Dont sweat the calculus notation read this as
the change in N over a period of time is equal to
the per capita rate of increase times N. Well,
maybe the calculus was better. ?
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Exponential Growth

• Exponential population growth
• Is population increase under idealized conditions
• Under these conditions
• The rate of reproduction is at its maximum,
  called the intrinsic rate of increase

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• The equation of exponential population growth is

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• Exponential population growth
• Results in a J-shaped curve

Dont forget the dN/dt is another way to say the
SLOPE of a line (the steepness of the curve)
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• The J-shaped curve of exponential growth
• Is characteristic of some populations that are
  rebounding

Notice that the slope is getting steeper and
steeper at each interval
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• Concept 52.4 The logistic growth model includes
  the concept of carrying capacity
• Exponential growth
• Cannot be sustained for long in any population
• A more realistic population model?
• Limits growth by incorporating carrying capacity

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

What biotic and abiotic components factor into
the carrying capacity?
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The Logistic Growth Model

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

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• We construct the logistic model by starting with
  the exponential model
• And adding an expression that reduces the per
  capita rate of increase as N increases

• The logistic growth equation
• Includes K, the carrying capacity

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• A hypothetical example of logistic growth

Notice the number we add to the population
declines as a function of increasing population
size
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• The logistic model perfectly fits few real
  populations
• But is useful for estimating possible growth

As populations get larger, their intrinsic rate
of growth approaches zero
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• The logistic model of population growth
• Produces a sigmoid (S-shaped) curve

Environmental resistance
Figure 52.12
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The Logistic Model and Real Populations

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

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

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• Some populations
• Fluctuate greatly around K

K?