1Population biology• Demography: study of how the vital rates of individuals(birth, death, growth, migration) affect structure anddynamics of populations• Population: group of potentially interbreeding individuals(same species, co-occur in time and space)– density: number of individuals per area or volume––size structuresize structure––age distributionage distribution––sex ratiosex ratio……2BIDE Equationfor change inpopulation size,N:!N (numbers in population) =Births + Immigration - Deaths -Emigration3Dispersion: pattern of distributionof individuals in space (clumped,even, or random = every site has anequal probability of being occupiedby an individual, independent oflocations of other individuals)4Parent GanetchicksA peck apart…5Intraspecific interactions (between individuals ofthe same species) vsInterspecific interactions (between individuals ofdifferent species)Life (and reproductive) table—summary of age (orsize) specific rates of survival and fecundity(progeny per individual)Constructed by following a cohort: a group ofindividuals of the same age, from birth until theyall die (or by other methods that approximatethis ideal approach) .6“Of course, long before you mature, most of you will be eaten.”7891011Cohort life table (for reproductives only):ax - number surviving to age xllxx –– proportion original cohort alive at proportion original cohort alive attime (age) xtime (age) xmmxx –– fecundity of individual at age x fecundity of individual at age xlx mx – number of progeny contributed per original individual of age xBasic Reproductive RateBasic Reproductive RateRRoo = = "" llxx m mxx Ro is sum of progenyproduced per originalindividual at the endof the cohort’s life.If Ro > 1, populationgrows.12Age structure of human population reflects age-specific birthand death rates13Population growth (Nt = number of individuals at time t)! N = Births – Deaths (population closed to migration)! N = Births + Immigration – Deaths – Emigration (open pop.)!N /! t = rate of changedN/dt = rate of change over very small time intervalb = per capita birth rate (number of births/(Nt-1time-1) = time-1if Nt = 1000 and there were 34 births in a year, b = 0.034 year -1 d = per capita death rate (deaths Nt-1 time-1) = time-1)if Nt = 1000 and there were 16 deaths in a year,d = 0.016 year -1 dN/dt = bNt – dNt = (b – d) Nt = r Nt (closed population)r = b – d = per capita rate of population growth (time -1 )14dN/dt = b Nt – d Nt = (b – d) Nt = r Nt !Nt= Noert (e = 2.71828… = base natural logarithm)r = per capita rate of increaseN = numbers of individuals in populationt = time15TimeDensity, Nr > 0r = 0r < 0dN = rN dtIf r > 0,population growsexponentially.If r = 0,population is in astable equilibrium(zero populationgrowth), althoughindividuals ‘turnover’ (some die,and are replacedby new births).If r < 0,populationdeclinesexponentially(until it goesextinct).Nt= Noert16Elephants in Kruger National Park South Africa17Billions ofpeople1650 – 0.51850 – 11930 – 21975 – 42000 – 61819Huge effect of age of first reproduction onpopulation size in an expanding populationYearsB = 2, N(4) = 16B = 3, N(4) = 9B = 8, N(4) = 8B = brood sizeN(t) = population size at time tA = age at 1st reproductionA = 1 A = 2 A = 420Campbell, Fig. 52.11K = carryingcapacity ofpopulation in agivenenvironmentK depends onboth theenvironmentand theorganism inquestion21Campbell, Fig. 52.13--density dependence in per capita birthand death rates (due to intraspecific (within species) competition(mutually adverse interaction))Per capita = per individual birth or death rates22overshootTerritorialitycan producethis type ofpopulationgrowthDensityindependentfactors?23NTimeChange in limitingfactorPeriod oflooserregulatione.g. speed limit, versusregulation by enforcementof minimum and maximumspeed24Analogy: speed limit (60 mph) regulatedstrictly (55-65) or loosely (40-80).SpeedingOver-steeringDistracted drivers• Rapid population growthrate (r)• Strong density-dependent feedbacks• Time lags in feedbacksNTime25Demographic transition, change from ZPG due to highdeath rate to ZPG due to low birth rate26r* vs K* selected life history traits• r-selected traits– Short life span– Small size– High predatorvulnerability– Weak competitor– Good disperser– Many smalloffspring– Early reproduction• K-selected traits– Long life span– Large size– Low vulnerability topredators– Strong competitor– Slower disperser– Fewer but betterprovisioned offspring– Late
View Full Document
Unlocking...