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POPULATION GROWTH. What is a population?. A group of organism of the same species living in the same habitat at the same time where they can freely interbreed. © 2010 Paul Billiet ODWS. How can populations change?. Natality Mortality Immigration Emigration. © 2010 Paul Billiet ODWS.

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POPULATION GROWTH


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what is a population
What is a population?
  • A group of organism of the same species
  • living in the same habitat
  • at the same time
  • where they can freely interbreed

© 2010 Paul Billiet ODWS

how can populations change
How can populations change?
  • Natality
  • Mortality
  • Immigration
  • Emigration

© 2010 Paul Billiet ODWS

natality
Natality
  • Increases population size
  • Each species will have its own maximum birth rate
  • Maximum birth rates are seen when conditions are ideal
  • This can lead to exponential growth

© 2010 Paul Billiet ODWS

mortality
Mortality
  • Mortality reduces population growth
  • It operates more when conditions are not ideal
  • Overcrowding leading to competition, spread of infectious disease

© 2010 Paul Billiet ODWS

immigration
Immigration
  • It increase population growth
  • It operates when populations are not completely isolated

© 2010 Paul Billiet ODWS

emigration
Emigration
  • It decrease population growth
  • It operates when populations are not completely isolated

© 2010 Paul Billiet ODWS

interactions
Interactions

Population growth =

(Natality + Immigration) - (Mortality + Emigration)

© 2010 Paul Billiet ODWS

population growth9

Numbers

Time

Population growth

K

3

2

1

© 2010 Paul Billiet ODWS

phases of population growth
Phases of population growth

Phase 1: Log or exponential phase

  • Unlimited population growth
  • The intrinsic rate of increase (r)
  • Abundant food, no disease, no predators etc

Phase 2: Decline or transitional phase

  • Limiting factors slowing population growth

© 2010 Paul Billiet ODWS

phase 3
Phase 3

Plateau or stationary phase

  • No growth
  • The limiting factors balance the population’s capacity to increase
  • The population reaches the Carrying Capacity (K) of the environment
  • Added limiting factors will lower K
  • Removing a limiting factor will raise K

© 2010 Paul Billiet ODWS

factors affecting the carrying capacity
Factors affecting the carrying capacity
  • Food supply
  • Infectious disease/parasites
  • Competition
  • Predation
  • Nesting sites

© 2010 Paul Billiet ODWS

modelling population growth the maths
Modelling population growth, the maths
  • Population growth follows the numbers of individuals in a population through time. The models try to trace what will happen little by little as time passes by
  • A small change in time is given by ∆t This is usually reduced to dt
  • Time may be measured in regular units such as years or even days or it may be measured in units such as generations
  • A small change in numbers is given by ∆NThis is usually reduced to dN
  • A change in numbers as time passes by is given by: dN/dt

© 2010 Paul Billiet ODWS

exponential growth
Exponential growth

Numbers

Time

© 2010 Paul Billiet ODWS

exponential growth15
Exponential growth
  • The J-shaped curve
  • This is an example of positive feedback
  • 1 pair of elephants could produce 19 million elephants in 700 years

© 2010 Paul Billiet ODWS

modelling the curve
Modelling the curve
  • dN/dt= rN
  • r is the intrinsic rate of increase
  • Example if a population increases by 4% per year
  • dN/dt= 0.04N

© 2010 Paul Billiet ODWS

real examples of exponential growth
Real examples of exponential growth
  • Pest species show exponential growthhumans provide them with a perfect environment
  • Alien speciesWhen a new species is introduced accidentally or deliberately into a new environment It has no natural predators or diseases to keep it under control

© 2010 Paul Billiet ODWS

european starling sturnus vulgaris
European starling (Sturnus vulgaris)
  • Between 1890 and 1891, 160 of these birds were released in Central Park New York.
  • By 1942 they had spread as far as California.
  • An estimate population of between 140 and 200 million starlings now exist in North America
  • One of the commonest species of bird on Earth

Image Credit: http://www.columbia.edu/

© 2010 Paul Billiet ODWS

the colorado beetle leptinotarsa decemlineata

© P Billiet

The Colorado Beetle (Leptinotarsa decemlineata)
  • A potato pest from North America
  • It spread quickly through Europe

© 2010 Paul Billiet ODWS

r strategists boom and bust
r-strategists boom and bust!
  • Maximum reproductive potential when the opportunity arrives
  • Periodic population explosions
  • Pests and pathogens (disease causing organisms) are often r-species

© 2010 Paul Billiet ODWS

the carrying capacity
The Carrying Capacity
  • Darwin observed that a population never continues to grow exponentially for ever
  • There is a resistance from the environment
  • The food supply nesting sites decrease
  • Competition increases
  • Predators and pathogens increase
  • This resistance results from negative feedback

© 2010 Paul Billiet ODWS

slide25

K

Numbers

Time

© 2010 Paul Billiet ODWS

the carrying capacity26
The Carrying Capacity
  • This too can be modelled
  • It needs a component in it that will slow down the population growth as it reaches a certain point, the carrying capacity of the environment (K)
  • The equation is called the logistic equation
  • dN/dt = rN[(K-N)/N]
  • When N<K then dN/dt will be positivethe population will increase in size
  • When N=K then dN/dt will be zerothe population growth will stop
  • Should N>K then dN/dt will become negativethe population will decrease

© 2010 Paul Billiet ODWS

k strategists long term investment
K-strategists long term investment
  • These species are good competitors
  • They are adapted to environments where all the niches are filled
  • They have long life spans
  • Lower reproductive rates but …
  • High degree of parental care thus …
  • Low infant mortality
  • K-strategist flowering plants produce fewer seeds with a large amount of food reserve

© 2010 Paul Billiet ODWS