1Unitary vs Modular organisms• Unitary organismsdevelop from zygote toadult with determinantform• Modular organisms growby repeated interationsof its parts (modules)into an adult ofindeterminate form(coral, poison oak)– Genet: genetic individual,all the biomass thatderived from single embryo– Ramet: subunit of genetthat is physiologicallyviable as an autonomousfragment2Currencies: energy, nutrients, timegrowth maintenanceactivityReproduction:offspring qualityoffspring quantityAllocation?unitarymodular3Life history trade offsLife history trade offs of plants oranimals• Starting growth early in theseason entails risk of freezing• If reproductive resourcesallocated to larger seeds, plantmakes fewer, so incurs morepredation risk, and risk of badluck (unfavorable microsites)• Dispersal: reduces competitionwith parent, but increases risk ofunsuitable habitat.Bet hedging by searocket—half the seedpod floats, half sinks4Life history tradeoffsAllocation to reproductioncomes at expense ofindividual’s own growth, andpossibly survival (and viceversa)If resources are storedrather than spent onoffspring, a plant canquickly replace tissue lostto grazing, fire, wind, andcan survive over periods ofstarvation (e.g. deciduoustrees in winter)Fig 52.6, Campbell5Trade-offs6Population biology• Demography: study of how the vital rate of individuals(birth, death, growth) affect structure and dynamics ofpopulations• 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……752.352.2Dispersion: 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)8Parent GanetchicksA peck apart…9Intraspecific 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 acohort: a group of individuals of the same age,from birth until they all die (or by other methodsthat approximate this ideal approach) .10T52.1T52.111T52.2T52.21252.552.3“Of course, long before you mature, most of you will be eaten.”1314Cohort 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.15Age structure of human population reflects age-specific birthand death rates16Huge 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 = 417Population 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 = b Nt – d Nt = (b – d) Nt = r Nt (closed population)r = b – d = per capita rate of population growth (time -1 )18dN/dt = b Nt – d Nt = (b – d) Nt = r Nt !Nt= Noert (e = 2.71828… = base natural logarithm)r, “intrinsic rate of natural increase”, is the per capitapopulation growth under the most favorable ofenvironmental circumstances, probably at low density.19TimeDensity, 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).20Human Population Explosion1650 – 0.51850 – 11930 – 21975 – 42000 – 6Billions ofpeople:2152.2252.20Billions ofpeople1650 – 0.51850 – 11930 – 21975 – 42000 – 6222324Campbell, 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 rates25Demographic transition, change from ZPG due to highdeath rate to ZPG due to low birth rate26*r describes population growth at low density, K describes density at which population stops growing.TimeNumbers in PopulationK0“Logistic equation”:dN/dt = rN [(K-N)/K]27Campbell, Fig. 52.11K = carryingcapacity ofpopulation in agivenenvironmentK depends onboth theenvironmentand theorganism inquestion28r* 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 reproduction29overshootTerritorialitycan producethis type ofpopulationgrowthDensityindependentfactors?30NTimeChange in limitingfactorPeriod oflooserregulatione.g. speed limit, versusregulation by enforcementof minimum and maximumspeed31Analogy: 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 feedbacksNTime32Fig. 52.23 Campbell: Ecological footprintEcological footprint: Estimateof land and water area neededto produce all resources anation consumes, and to absorball the waste it generatesCorrelateswith
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