Presentation on theme: "POPULATION GROWTH & MEASUREMENT"— Presentation transcript:
1 POPULATION GROWTH & MEASUREMENT AP Environmental ScienceChapter 6
2 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 thatenter or leave the population
3 Population Graphs measure status of populations J-curve or Exponential Growth CurveS-Curve or Logistics Curve
4 POPULATION DENSITYDENSITY: number of individuals per unit area or volumeEx: Suppose there are150 bullfrogs living in apond that covers anarea 3 square km.What is the population density?
5 Population density Population Density = Number of Individuals (150 frogs)Unit Area (3 sq KM)= 50 bullfrogs per square kilometer!
7 CARRYING CAPACITY Max population that a habitat can support EDATOSFODDISEADISAsTER=Max population that a habitat can support(Level line)
8 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
9 Other factors – H I P P O can decrease in population!! H=HabitatI= Invasive speciesP= PollutionP=Other interacting populationsO=Overconsumption
10 Exponential Increase (J-curve) In a J-curve, the popul keeps growing quickly (exponentially over time).
11 What causes J-curve to occur? Conditions:No enemiesNo competition.Plenty of food & water4. Low % of diseaseJ-curve is usually a temporary situation=Population crash.
12 Exponential Growth Math Model Change in NChange in timeInitial PopulationRate of reproductionTime
13 dN/dt = rN Time (dt) N (dN) Rate (r)* r x N Exponentially how does it look for aJ-curveT121010x2 = 202x10T22010x20=2002x10x10T320010x200=2,0002x10x10x10200010x2,000=20,0002x10x10x10x10T420,00010x20,000=200,0002x10x10x10x10x10N=2 cockroaches (male and female)r= 2 cockroaches can produce 20 offspring in 3 monthsa. The rate of growth (r) 20/2 adults or 10 per 1 adult.b. The growth rate (r) equals 10
15 Exponential Growth can Crash When population can no longer sustain itself without food resources, pop decrease beneath the carrying capacity.
16 Population Crash Isle Royale, Michigan National Park Moose pop quickly inWolf pop due toParvovirus passed on from domesticated dogs visiting the National Park.Moose populationDue to tick infestation.
18 S-curve or Logistics Population 1. Population at equilibrium.S-curve may change (increase & decrease) slightly, but is constant near the carrying capacity.May be considered “restricted growth”.
19 Factors that keep populations within carrying capacity Migration
20 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
21 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:1001- 1 = 0dN/dt = rN(0)=0!!!
22 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.
23 Logistics & CC (continued) If N = 10…plug into 1-N/K(1- 10) = (1-.10) = .90100dN = rN(.90) or dN is at a rate ofdt dt90% as fast as the max possible reproductive rate for the wolves!
24 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 n2N n m2n1=#animal marked & released 1st timen2=# animals captured during 2nd sessionm2-# animals captured during 2nd session & are marked.Est Population
25 Population Measurement in Review J-curveExponential CurveS-curveLogistics CurveCarrying Capacity
26 Population Equilibrium Equilibrium: the balance between births and deaths within a population
27 Other Population Considerations Environmental ResistancePopulation DispersalReproductive Potential
28 Environmental Resistance Factors/pressures that limit a population’s ability to increase (CC)Density DependentDensity IndependentParasitesTemperatureDiseaseMoisture, light, pH salinityCompetitorsWeatherPredatorsNatural DisastersHuman InterventionLack of habitat/territory
29 Population Dispersal Definition Different patterns of how a species or population will inhabit a certain geographical location.
30 Population Dispersal is determined by: RandomUniformClumped
31 POPULATION DISPERSAL A. RANDOM: 1. Least Common 2. Found anywhere in envir.3. High mobility such as wind blownEx: Dandelions
32 POP DISPERSAL B. Uniform Rare Occurrence but does occur in nature! (Hawks, wolves)Can indicate human impacta. Plantations, orchards, etc.
33 UNIFORM POPULATION DISP. Red-Tailed HawkOrchards
34 CLUMPED POP DISPERSAL C. CLUMPED: Patchy, most common Protection, avail of natural resources, to surviveEx: Allelopathy, fish, plants, trees, etc.
35 Clumped Dispersal – Purple Loosestrife Patterns in US
36 Reproductive Potential …Is an organism’s ability to grow at the fastest rate.(To replenish the species—innate!)
37 REPRODUCTIVE POTENTIAL COMPARISON R-selectedHint: Rapid ReproEarly reproductionShort life spanHi mortalityLittle/no parental careLarge # of offspring producedInhabit lower trophic levels (1st order consumers)2. K-selectedHint: Longer ReproLate reproductionLong life spanLow mortalityHigh parental careSmall # of offspring produced
39 Reproductive potential – “R” Bacterium can produce 19 million descendants in a few days!!Mosquitoes live days laying eggs every 3 days.Mosquito rafts have eggs;. hatch in 48 hours
40 Reproductive potential – “K” Some species have higher reproductive potential!!K-Potential GestationTimes:Human= 9 monthsElephants= 22 monthsOppossum = days (marsupial)
41 CRITICAL NUMBERSSurvival & recovery of population depends on a minimum population base—its critical number.
42 Factors Affecting Critical Number C1. IMMIGRATION: movement of indiv into an area C2. EMIGRATION: movement of individuals which leave an area. Plus Environmental Resistance Factors
43 Critical NumbersIf pop falls below critical number, breeding may fail and extinction could occur.Threatened: species whose pops are declining rapidlyEndangered: near critical number and may become extinct.