Lecture 2 Populations: Population GrowthWorld Population counterIt's Getting CrowdedDavid Attenborough videoFigure 5.6 Three Periods of Human Population GrowthPowerPoint PresentationSlide 7Figure 4.14 If Population Growth Were Driven by Birth Rate OnlySlide 9Slide 10Slide 11What does this suggest?Slide 13Figure 5.10 Birth Rate and WealthFigure 5.11 Comparing Birth Rates by AgeSlide 16Slide 17Slide 18Life TablesExponential model of growthSlide 21Slide 22Slide 23Slide 24Slide 25Slide 26Figure 4.21 Logistic GrowthFigure 4.22 Alternative Patterns of Population GrowthSlide 29Slide 30Slide 31Slide 32Lecture 2Populations: Population Growth•ECOL 1000: Ecological Basis of Environmental Issues•University of Georgia•Spring 2015World Population counterhttp://www.worldometers.info/http://www.census.gov/popclock/It's Getting CrowdedDavid Attenborough video© 2012 Pearson Education, Inc.Pre-agricultural period• grew as humans expandedinto new territories anddeveloped new tools• grew slowly over about 1 million yearsAAgricultural period• stimulated human populationgrowth• population grew more rapidlyover 7,000 yearsBIndustrial periodC• led to increased foodproduction andimproved sanitation,nutrition, medical care• population grew rapidlywithin three centuries20101700 A.D.5000 B.C.Figure 5.6 Three Periods of Human Population GrowthDarwin“There is no exception to the rule that every organic being naturally increases at so high a rate, that, if not destroyed, the earth would soon be covered by the progeny of a single pair”Introduction of European starlings into New York City Central Park in 1890Figure 4.14 If Population Growth Were Driven by Birth Rate OnlyIn just 20 years, a hypothetical population of 30 male and 30 female starlings will increase to over 4.5 trillion birds.Changes in a populationNBirthDeathImmigrationEmigration∆N = B+I-D-EBecause organisms have different life-histories, there is a need for two general models of population growth1) Exponential (Logistic) growthused for populations with continuous reproduction and/or overlapping generations2) Geometric growth used for populations with reproduction occurring at discrete intervalsdN dt = rN rate of change in population size(slope of line)=contribution ofeach individual to population growthXnumber of individuals in the populationRate of change in populationtimeNr = per-capita growth rate (exponential)What does this suggest?•Population growth is very rapid (exponential) and independent of density•But, of course, as more and more of the resources are taken up and become unavailable, the growth rate slows down and eventually becomes zero when all resources are used uptimeNAre Birth Rates (r) consistent throughout the world?Figure 5.10 Birth Rate and WealthFigure 5.11 Comparing Birth Rates by AgeHigher birth rates among younger women shortens generation time……leading to more children growing and reproducing……leading to higher population growth ratesWe’ve really been talking about population growth in terms of: births & deathsAnd, we’ve assumed that birth ratesand death rates are the same forall members of the populationMost populations have age structureIf we know something about age-specific survival and fecundity,we can project population size and age structure into the futureLife Tables •Life tables summarize age-specific schedules of survival and fecundity (typically for females) in a convenient format, including:–age (x)–number alive –probability of survival between–mortality rate –fecundity (reproductive output) •Cohort: A group of individuals of the same age-classExponential model of growthdN dt = rNExponential model of growthModels & Assumptions…Assumptions:–Essential resources are unlimited•Space•Food–Environment is constant•No seasonal or annual variationdN dt = rNAll populations must ultimately beControlled. Populations cannot increase forever!To reflect this, we create:carrying capacity (K) - number of individuals that the environmentcan support indefinitelydN dt = rNNK()1So, now 2 components of equation:Logistic model of population growthWhy add second component? What is its function?It reduces population growth as population size approaches carrying capacitydN dt = rN• If N is small (~0), 1 - 0 = 1, term cancels out and you have maximum exponential growth (rN)• As N approaches K, rN is multiplied by a very small number, so population growth rate (dN/dt) slows WAY downNK()1Can N (population size) ever exceed K (carrying capacity)? How? What would happen?Logistic Growth CurveInflection pointFast population growth (exponential) at low N, then what?© 2013 Pearson Education, Inc.Figure 4.21 Logistic Growth© 2013 Pearson Education, Inc.Figure 4.22 Alternative Patterns of Population GrowthWhat types of factors control population growth or size?Density-dependent factorsFactors that influence population growthin accordance with population size (e.g. change births and deaths)Density-independent factorsFactors that affect population growth regardless of population sizeDensity-dependent factors• resource availability• competition• disease• temperature• precipitation• catastrophic disturbancesDensity-independent factorsRegulation:Tendency of a population todecrease in size when above acertain level (e.g., K), and increase in size below that levelBy definition, population regulation must be density-dependentPopulations can ONLY be regulated by