population growth & measurement
DESCRIPTION
POPULATION GROWTH & MEASUREMENT. AP Environmental Science Chapter 6. WHAT IS A POPULATION?. A group of interbreeding individuals within a geographical location. POPULATION SIZE is determined by: #of births (based on fertility rates) # of deaths # of indiv that - PowerPoint PPT PresentationTRANSCRIPT
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POPULATION GROWTH & MEASUREMENT
AP Environmental ScienceChapter 6
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WHAT IS A POPULATION?
A group of interbreeding individuals within a geographical location.
POPULATION SIZE is determined by:
a. #of births (based on fertility rates)
b. # of deathsc. # of indiv that enter or leave the
population
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Population Graphs measure status of populations
J-curve or Exponential Growth Curve
S-Curve or Logistics Curve
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POPULATION DENSITYDENSITY: number of
individuals per unit area or volume
Ex: Suppose there are 150 bullfrogs living in apond that covers an area 3 square km. What is the population
density?
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Population density
Population Density =
Number of Individuals (150 frogs) Unit Area (3 sq KM)
= 50 bullfrogs per square kilometer!
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Populations Dynamics
http://www.hippocampus.org/course_locator?course=AP%20Biology%20II&lesson=63&topic=1&width=600&height=454&topicTitle=Population%20Ecology:%20Overview&skinPath=http://www.hippocampus.org/hippocampus.skins/default
Population Modeling
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CARRYING CAPACITY
Max population that a habitat can support
(Level line)
DISEASE
DISAsTERS
=
PREDATORS
FOOD
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Carrying Capacity Factors
These limiting pressures keep a population in check such as carrying capacity:1. # of Predators2. Amount of Food & Water ResourcesDiseaseNatural DisastersReproductive ability
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Other factors – H I P P O can decrease in population!!
H=Habitat I= Invasive species P= Pollution P=Other interacting populations O=Overconsumption
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Exponential Increase (J-curve)
In a J-curve,the popul keepsgrowing quickly(exponentially
over time).
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What causes J-curve to occur?
Conditions:1. No enemies2. No competition.3. Plenty of food & water4. Low % of disease J-curve is usually a temporary
situation=Population crash.
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Exponential Growth Math Model
Rate of reproduction
Initial Population
Time
Change in N
Change in time
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dN/dt = rNTime (dt)
N(dN)
Rate (r)*
r x N Exponentially how does it look for a J-curve
T1 2 10 10x2 = 20 2x10
T2 20 10 10x20=200 2x10x10
T3 200 10 10x200=2,000 2x10x10x10
T3 2000 10 10x2,000=20,000 2x10x10x10x10
T4 20,000 10 10x20,000=200,000 2x10x10x10x10x10N=2 cockroaches (male and female)r= 2 cockroaches can produce 20 offspring in 3 months
a. The rate of growth (r) 20/2 adults or 10 per 1 adult.b. The growth rate (r) equals 10
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Figure 06_03
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Exponential Growth can Crash
When population can no longer sustain itself without food resources, pop decrease beneath the carrying capacity.
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Population Crash
Isle Royale, MichiganNational Park
Moose popquickly in 1991-1995.
Wolf pop due toParvovirus passed on from domesticated dogs visiting the National Park.
Moose population Due to tick infestation.
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S-curve (Logistics curve)
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S-curve or Logistics Population
1. Population at equilibrium.
2. S-curve may change (increase & decrease) slightly, but is constant near the carrying capacity.
3. May be considered “restricted growth”.
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Factors that keep populations within carrying capacity
Migration
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Logistics Curve Model
dN = rN 1-N dt K
dN = change of population over timedtN = PopulationK= Current Carrying Capacityr= rate of change or reproductive rate of a speciesd
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Logisitics/Carrying Capacity Connection
If the carrying capacity (K) = 100 wolvesIf the N = 100 wolves (wolves bred successfully to increase population)Look at the 1-N/K part: 1 - 100
100 1- 1 = 0
dN/dt = rN(0)=0!!!
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Logistics & CC (continued)
There is no change in dN/dt-no population growth!
What if N=50? Plug it into 1-N/K to see how it affects the reproductive rate for a population. 1-50/100 = 1-1/2 = 1/2rN or half of the maximum reproductive rate for the wolves.
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Logistics & CC (continued)
If N = 10…plug into 1-N/K(1- 10) = (1-.10) = .90 100dN = rN(.90) or dN is at a rate of dt dt
90% as fast as the max possible reproductive rate for the wolves!
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Lincoln Peterson Population Estimate Model
Estimating population size by random sampling an ecosystem.Focus on population density or animal abundance. Model: n1 = m2 OR N= n1 x n2 N n2 m2n1=#animal marked & released 1st time n2=# animals captured during 2nd sessionm2-# animals captured during 2nd session & are marked.
Est Population
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Population Measurement in Review
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Population Equilibrium
Equilibrium: the balance between births and deaths within a population
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Other Population Considerations
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Environmental Resistance
Factors/pressures that limit a population’s ability to increase (CC)
Density Dependent Density Independent
Parasites Temperature
Disease Moisture, light, pH salinity
Competitors Weather
Predators Natural Disasters
Human Intervention Lack of habitat/territory
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Population Dispersal Definition
Different patterns of how a species orpopulation will inhabit a certaingeographical location.
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Population Dispersal is determined by:
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POPULATION DISPERSAL
A. RANDOM: 1. Least Common2. Found anywhere in
envir.3. High mobility such
as wind blown Ex: Dandelions
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POP DISPERSAL
B. Uniform1. Rare Occurrence but does occur
in nature! (Hawks, wolves)
2. Can indicate human impact a. Plantations, orchards, etc.
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UNIFORM POPULATION DISP.
Orchards
Red-Tailed Hawk
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CLUMPED POP DISPERSAL
C. CLUMPED:1. Patchy, most
common2. Protection, avail of
natural resources, to survive
3. Ex: Allelopathy, fish, plants, trees, etc.
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Clumped Dispersal – Purple Loosestrife Patterns in US
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Reproductive Potential
…Is an organism’s ability to grow at the fastest rate.
(To replenish the species—innate!)
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REPRODUCTIVE
POTENTIAL COMPARISON
1. R-selectedHint: Rapid Reproa. Early reproductionb. Short life spanc. Hi mortalityd. Little/no parental caree. Large # of offspring
producedf. Inhabit lower trophic
levels (1st order consumers)
2. K-selected Hint: Longer Reproa. Late reproductionb. Long life spanc. Low mortalityd. High parental caree. Small # of offspring
produced
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REPRODUCTION TYPES
K-SELECTED TYPE
R-SELECTED TYPES
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Reproductive potential – “R”
Bacterium can produce 19 million descendants in a few days!!
Mosquitoes live 10-14 days laying eggs every 3 days.
Mosquito rafts have 200-300 eggs;. hatch in 48 hours
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Reproductive potential – “K”
Some species have higher reproductive potential!!
K-Potential Gestation Times:Human= 9 monthsElephants= 22 monthsOppossum = 12-13
days (marsupial)
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CRITICAL NUMBERS
Survival & recovery of population depends on a minimum population base—its critical number.
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Factors Affecting Critical Number
C1. IMMIGRATION: movement of indiv into an areaC2. EMIGRATION: movement of individuals which leave
an area. Plus
Environmental Resistance Factors
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Critical Numbers
If pop falls below critical number, breeding may fail and extinction could occur.
Threatened: species whose pops are declining rapidly
Endangered: near critical number and may become extinct.