Population Dynamics

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First found May 22, 2018

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population
 Number of members of a single species in a
particular area
Demography
 Demography – study of (human) populations,
make-up and distribution
 Demo = people
 Graph = picture/diagram
 Ex: Commercials during cartoon programs are
often for toys because their target demographic
is children
 Term is expanded to suit all species’
populations
3 characteristics of all
populations
Density
 The number of organisms of the same species
per unit area (25 people per classroom)
Dispersion
 The pattern of population distribution
Ranges
 Limited by biotic and abiotic factors
Population density
 The number of organisms per unit area.
 High population density = crowded
So cities have…
High people population density, but low…
Trees and other organisms that got displaced
Dispersion
 often dictated by availability of
food.
 Uniform dispersion
 Evenly spaced
 Territorial animals protect their
hunting grounds, creating this.
 Clumped dispersion
 Social animals that live in herds or
colonies
 Examples?
 Buffalo, ants, bees, wildebeast,
schools of fish
Dispersion continued
 Random dispersion
 Neither territorial nor colonizing
 Unpredictable
 Examples:
 Deer, many birds (except when they group
together to migrate)
Range
 Can be very small, like…
 limited to an island
 Or vast, like …
 almost everywhere on the planet
 Mosquitos
 Range is determined by both biotic and abiotic
factors
Population Limiting Factors
Density independent factors
 Factors that do/don’t (pick one) depend on
the population density
 Don’t
 So abiotic factors, such as weather events,
including
 Drought, flood, fire, tornados
Population Limiting Factors
Density dependent factors
 Biotic factors limit the population
 Amount of food (plants or prey)
 Amount of predators
 Amount of competition for same resource
 The higher the population, the more
competition
 Disease (higher rate with higher population
density)
Population growth rate
Emigration:
 Leaving the population
Immigration
 Coming in to the population
 Pop. by:
 emigration and mortality (death)
 Pop. by:
 Immigration and birth
Population growth rate
 If population increase and decrease are equal,





then population growth rate is …
Zero
If immigration and birth exceed (are greater than,
>) emigration and death, then population growth
rate is
Positive
What are the factors that make population growth
negative?
More deaths and emigration than births and
immigration.
Growth models
 Exponential and logistical
growth models
Exponential
 All pop’s. would do this if
not limited
 Happens when a
population arrives in a new
area with no competition
and plenty of food
Exponential growth
Exponential growth
Growth Models
Logistical
 S curve
 Exponential growth until limiting factors bring
under control
 Then stable
Carrying capacity
 The maximum number of individuals of a
species an area can support over the long
term
 Limited by biotic (predation, food availability)
and abiotic (land, space for nesting, etc)
factors
Survivorship
 survivorship – % of members of a group likely to survive to any
given age
 Type I –Most members of the species survive into old age
 Type II – steady decline
 Type III – high infant mortality (many offspring; many die
young)
Survivorship & Life Histories
 Limited energy
 Can’t both put energy into lots of offspring
AND lots of care
 Many factors determine which it will be
 Semelparity: “big bang” reproduction. All
energy is focused into producing many
offspring before dying
 Iteropartiy: (iterations) cyclical reproductive
pattern. Only a few offspring per cycle,
usually cared for.
Reproductive patterns

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






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r-strategists and k-strategists
r-strategists
Produce many offspring
Don’t spend much energy caring
for young
most offspring die, best adapted
survive
Typical for fluctuating
environment
Examples
Dandelions,
sponges,
sea turtles
Reproductive patterns
 k-strategist
 Tend to be larger animals
 Produce few offspring
 Care for their young
 Most offspring survive
 Environmental conditions
generally stable
 Controlled by density
dependent factors
 Examples
 Most mammals, large birds,
R-strategist or k-strategist?
Modeling Populations
http://www.bozemanscience.com/apb-practice1-models-representations
 N = population size now
 B = # births
 b = # births per capita = birth RATE
 D or M = deaths or mortality
 d or m = deaths per capita = death RATE
 T = time, usually 1 generation
 r = b – d = population rate of change
 ∆N = change in population
Exponential Growth
 ∆N = rN
 New N = ∆N + N
Logistic Growth
 ∆N = rN(K-N)/K
 Takes into account the carrying capacity
Population Pyramid,
AKA: Age Structure Diagram
 Shows gender and age distribution at a fixed time
 Shape below shows many children born (high total
birth rate), but also high infant mortality
 This is a developing country age structure
 Population is increasing rapidly
Population Pyramids
AKA Age Structure Diagram
 Here you see the US vs. Nigeria
 US birth rate is approximately equal to death rate
and population has stabilized
Ecological Footprint
 Populations use resources at different rates
 Ecological capactiy: Different lands have differing amounts of
resources to offer.
 Ecological footprint: the aggregate land and water area
appropriated by each nation (or individual) to produce all the
resources it consumes and absorb all the waste it generates.

Http://www.footprintnetwork.org/ar/index.php/GFN/page/footprint_for_nations/#
Ecological creditors and debtors
http://www.footprintnetwork.org/ar/index.php/GFN/page/ecological_debtors_and_creditors/
Countries that use more than their biocapacity are creditors. Countries
using less are debtors.
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