population growth & measurement
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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
POPULATION GROWTH & MEASUREMENT
AP Environmental ScienceChapter 6
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
Population Graphs measure status of populations
J-curve or Exponential Growth Curve
S-Curve or Logistics Curve
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?
Population density
Population Density =
Number of Individuals (150 frogs) Unit Area (3 sq KM)
= 50 bullfrogs per square kilometer!
Populations Dynamics
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Population Modeling
CARRYING CAPACITY
Max population that a habitat can support
(Level line)
DISEASE
DISAsTERS
=
PREDATORS
FOOD
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
Other factors – H I P P O can decrease in population!!
H=Habitat I= Invasive species P= Pollution P=Other interacting populations O=Overconsumption
Exponential Increase (J-curve)
In a J-curve,the popul keepsgrowing quickly(exponentially
over time).
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.
Exponential Growth Math Model
Rate of reproduction
Initial Population
Time
Change in N
Change in time
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
Figure 06_03
Exponential Growth can Crash
When population can no longer sustain itself without food resources, pop decrease beneath the carrying capacity.
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.
S-curve (Logistics curve)
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”.
Factors that keep populations within carrying capacity
Migration
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
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!!!
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.
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!
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
Population Measurement in Review
Population Equilibrium
Equilibrium: the balance between births and deaths within a population
Other Population Considerations
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
Population Dispersal Definition
Different patterns of how a species orpopulation will inhabit a certaingeographical location.
Population Dispersal is determined by:
POPULATION DISPERSAL
A. RANDOM: 1. Least Common2. Found anywhere in
envir.3. High mobility such
as wind blown Ex: Dandelions
POP DISPERSAL
B. Uniform1. Rare Occurrence but does occur
in nature! (Hawks, wolves)
2. Can indicate human impact a. Plantations, orchards, etc.
UNIFORM POPULATION DISP.
Orchards
Red-Tailed Hawk
CLUMPED POP DISPERSAL
C. CLUMPED:1. Patchy, most
common2. Protection, avail of
natural resources, to survive
3. Ex: Allelopathy, fish, plants, trees, etc.
Clumped Dispersal – Purple Loosestrife Patterns in US
Reproductive Potential
…Is an organism’s ability to grow at the fastest rate.
(To replenish the species—innate!)
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
REPRODUCTION TYPES
K-SELECTED TYPE
R-SELECTED TYPES
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
Reproductive potential – “K”
Some species have higher reproductive potential!!
K-Potential Gestation Times:Human= 9 monthsElephants= 22 monthsOppossum = 12-13
days (marsupial)
CRITICAL NUMBERS
Survival & recovery of population depends on a minimum population base—its critical number.
Factors Affecting Critical Number
C1. IMMIGRATION: movement of indiv into an areaC2. EMIGRATION: movement of individuals which leave
an area. Plus
Environmental Resistance Factors
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.