Population growth
This presentation is the property of its rightful owner.
Sponsored Links
1 / 34

Population Growth PowerPoint PPT Presentation


  • 80 Views
  • Uploaded on
  • Presentation posted in: General

Population Growth. December 7, 2010 Text p . 660-669. Population Dynamics. Populations always changing in size Deaths, births Main determinants (measured per unit time): Natality = number of births Mortality = number of deaths Emigration = # of individuals that move away

Download Presentation

Population Growth

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Population growth

Population Growth

December 7, 2010

Text p. 660-669


Population dynamics

Population Dynamics

  • Populations always changing in size

    • Deaths, births

  • Main determinants (measured per unit time):

    • Natality = number of births

    • Mortality = number of deaths

    • Emigration = # of individuals that move away

    • Immigration = # of individuals that move into an existing population


Effect on determinants

Effect on Determinants

  • The determinants vary from species to species

  • Environmental Conditions

  • Fecundity

    • Potential for a species to produce offspring in one lifetime

vs.


Limits on fecundity

Limits on Fecundity

  • Fertility often less than fecundity

    • Food availability

    • Mating success

    • Disease

    • Human factors

    • Immigration/Emigration


Survivorship

Survivorship

  • 3 patterns in survivorship of species

  • Type I

    • Low mortality rates until past reproductive years

    • Long life expectancy

    • Slow to reach sexual maturity, produce small numbers of offspring


Type ii

Type II

  • Uniform risk of mortality throughout life


Type iii

Type III

  • High mortality rates when they are young

  • Those that reach sexual maturity have reduced mortality rates


Calculating changes in population size

Calculating Changes in Population Size

Population Change = [(birth + immigration) – (deaths + emigration)] x 100

(%)initial population size (n)

  • Can be used to calculate growth rate of a population in a give time period

  • Positive Growth: Birth + Immigration > Death + Emigration

  • Negative Growth: Birth + Immigration <Death + Emigration


Open closed population

Open/Closed Population

  • Growth can depend on type of population

  • Open: influenced by natality, mortality and migration

  • Closed: determined by natality and mortality alone


Biotic potential

Biotic Potential

  • The maximum rate a population can increase under ideal conditions

  • Or intrinsic rate of natural increase

  • Represented as r


Carrying capacity

Carrying Capacity

  • Maximum number of organisms sustained by available resources

  • Represented as k


Population growth models

Population Growth Models

  • Basic model

    • No inherent limit to growth

Hypothetical model


Geometric growth model

Geometric Growth Model

  • In humans, growth is continuous (deaths and births all times of year)

  • In other organisms deaths may be year round, but births may be restricted

  • Population typically grows rapidly during breeding season only

  • Growth rate is constant at fixed intervals of time (breeding seasons)


Geometric growth model1

Geometric Growth Model

λ = the geometric growth rate

N = population size

t = time

N (t + 1) = population size in year X

λ = N (t + 1) or N(t + 1) = N(t) λ

N (t)

So...

N(t) = N(0) λt


Population growth

Initial population of 2000 harp seals, gives birth to 950 pups, and during next 12 months 150 die

Assuming geometric growth, what is the population in 2 years?

Year 1, Population Change = 950 births – 150 deaths

= 800

Initial Population N(0) = 2000

Population at end of Year 1, N(1) = 2000 + 950 – 150

Geometric Growth Rate (λ) = 2800 = 1.4

2000

Year 2 (t = 2): N(t) = N(0) λt

N(2) = (2000) (1.4)2 = 3920


Exponential growth model

Exponential Growth Model

  • Populations growing continuously at a fixed rate in a fixed time interval

  • The chosen time interval is not restricted to a particular reproductive cycle

  • Can determine the instantaneous growth rate, which is the intrinsic (per capita) growth rate


Population growth

Intrinsic growth rate (r)

N = population size

dN = instantaneous growth rate of population

dt

Population Growth Rate:

dN = rN

dt

Population’s Doubling time (td) = 0.69

r


Population growth

2500 yeast cells growing exponentially. Intrinsic growth rate (r) is 0.030 per hour

Initial instantaneous growth rate: dN = rN

dt

= 0.030 x 2500

= 75 per hour

Amount of time for population to double in size:

Td = 0.69 = 0.69 = 23 hrs

r 0.030


Population growth

Population size after each of 4 doubling times:

Td = 23 hrs, initial population = 2500


Curve shapes

Curve Shapes

Exponential = J-shaped curve

Smooth vs. geometric, which fluctuates


Logistic growth model

Logistic Growth Model

  • Geometric and exponential assume population will grow at same rate indefinitely

  • This means intrinsic growth rate (r) is a maximum (rmax)

  • In reality, resources become limited over time

  • Population nears the ecosystem’s carrying capacity, and growth rate drops below rmax


Logistic growth model1

Logistic Growth Model

  • Growth levels off as size of population approaches its carrying capacity

    Instantaneous growth rate:

    rmax: maximum intrinsic growth rate

    N: population size at any given time

    K: carrying capacity of the environment


Logistic growth curve

Logistic Growth Curve

  • S-shaped curve (sigmoidal)

  • 3 phases

  • Lag, Log, Stationary

  • At stationary phase, population is in dynamic equilibrium


Population growth

  • Useful model for predictions

  • Fits few natural populations perfectly


R k selection

r & K Selection

  • Species can be characterized by their relative importance of r and K in their life cycle


R selected species

r-Selected Species

Carrying capacity, K

  • Rarely reach K

  • High biotic potential

  • Early growth

  • Rapid development

  • Fast population growth

Population numbers (N)

r-selected species

Time


K selected species

K-Selected Species

Carrying capacity, K

  • Exist near K most of the time

  • Competition for resources important

  • Fewer offspring

  • Longer lives

K-selected species

Population numbers (N)

Time


Population growth

Work:

Text Page 669, # 1-5


  • Login