population growth. what is a population? a group of organism of the same species living in the same...
TRANSCRIPT
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
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
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Mortality
Mortality reduces population growth It operates more when conditions are not ideal Overcrowding leading to competition, spread of
infectious disease
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Immigration
It increase population growth It operates when populations are not completely
isolated
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Emigration
It decrease population growth It operates when populations are not completely
isolated
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Interactions
Population growth = (Natality + Immigration) - (Mortality + Emigration)
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Population growth
K
Numbers
Time
1
23
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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
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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 Food supply Infectious disease/parasites Competition Predation Nesting sites
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Modelling population growth, the math 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 ∆N This is usually reduced to dN
A change in numbers as time passes by is given by: dN/dt
dtdN
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Exponential growth
Time
Numbers
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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
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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
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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
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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
© 2010 Paul Billiet ODWS
Image Credit: http://www.columbia.edu/
European starling (Sturnus vulgaris)
Current distribution
CJKrebs (1978) Ecology
The Colorado Beetle (Leptinotarsa decemlineata) A potato pest from North America It spread quickly through Europe
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The Colorado Beetle (Leptinotarsa decemlineata)
Begon, Townsend & Harper (1990) Ecology
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
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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
K
Time
Numbers
© 2010 Paul Billiet ODWS
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 positive
the population will increase in size When N=K then dN/dt will be zero
the population growth will stop Should N>K then dN/dt will become negative
the population will decrease
© 2010 Paul Billiet ODWS
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
Patterns of Dispersion
Environmental and social factors Influence the spacing of individuals in a population
Patterns of Dispersion: Clumped
Clumped dispersion Individuals aggregate in patches Grouping may be result of the fact that multiple
individuals can cooperate effectively (e.g. wolf pack to attack prey or antelope to avoid predators) or because of resource dispersion (e.g. mushrooms clumped on a rotting log)
Patterns of Dispersion: Uniform
Uniform dispersion
Individuals are evenly distributed
Usually influenced by social interactions such as territoriality
Patterns of Dispersion: Random
Random dispersion: position of each individual is independent of other individuals (e.g. plants established by windblown seeds).
Uncommon pattern.