Ecosystem ChangeLife constantly undergoing changePopulations change or evolveEcosystems evolve alsoChange in populations size: population dynamics (more detail later)Changes may include increase and decreases in population sizeGrowth CurvesPopulations inherent ability to exponentially increase population sizeThey don’tWhyPopulationsChange in size (total number of individuals)Change in density (number of individuals in a certain space)Change in age distribution (proportion of individuals in each age group)Change in habitat distributionClumpsResources may vary greatly from place to placeBetter protection against predatorsSome predator species increase chances of securing a meal—wolf packTemporary clumps for mating and care for youngPopulation MeasurementCount directlyMark the presence of individuals in a representative area and extrapolate to a larger areaEstimated based on sign of presence such as droppings, birdcalls, etc.Change in Population SizeIncreases are exponential, not arithmeticIncrease is proportional to number of individuals already presentJ-shaped growthExponential growth: slow at first, followed by increasingly faster rates of growth, also calledGeometric growth: growth follows a geometric pattern of increase (2,4,8,16)Rule of 70: divide 70 by annual percentage yields approximate doubling time in yearsS-shaped GrowthGrowth model starts off like J-shaped form, but rate of growth slows and ceases altogetherStabilizes at certain level, denoted as KEnvironmental resistance limits growth in S-shaped growthLogistic growthBiotic PotentialCapacity for growth“r”=intrinsic rate of increase if the population has unlimited resourcesMost populations grow at rate less than thisEnvironmental ResistanceAll factors that act to limit growthAbiotic: light, temperature, critical nutrientsBiotic: specialized niche, too many competitors, drought, low repro. rate, inability to fight disease or migrate or adaptCarrying CapacityBiotic potential and environmental resistance determine carrying capacity “K”Maximum # of individuals of given species that can be sustained indefinitely in a given space (area or volume)Growth rate decreases as size nears K, resources begin to dwindleReal WorldPopulation growth varies in complex waysMay show J- or S-shaped growth at various timesGrowth rates may hover around KKCarrying capacity not fixedStable in stable environments, population can hover above K or below K depending on environmental variablesPatternsRate of population decrease is faster than increase=population crash or diebackPopulation explosion followed by dieback is called irruptive of Malthusian growthGrowth RateDifference between birth and death rate over a period of timebirthrate=# of individuals born in a given time expressed as a proportion of the total population=rGrowth RateDeath rate=# of individuals who die in a given timeGrowth rate (r)=birth rate-death rater<0: population shrinksr>0: population growsr=0: population at zero population growthReproductive Strategiesr-selected or Malthusian:Opportunistic species in highly variable environmentsHigh growth rates—take advantage of infrequent favorable conditionsReproduction is rapid, with little care of offspringr-selectedHigh growth rates—take advantage of infrequent favorable conditionsPressures are density-independent: physical (abiotic) forces and predation limit growthSmaller sizer-selectedReproduction is rapid, with little care of offspring, many offspringSheer numbers and effective dispersalReproductive StrategiesK-selected or Logistic: relatively stable environment, numbers fluctuate within narrow range around KPopulation size limited by carrying capacityReproduction slower, considerable care of offspringK-selectedLarger sizePressures are density-dependent: as population increases, food and living space limit growthLive longer, mature slowly, fewer offspring/generationExamplesr-selected: rodents, many insects, marine invertebrates, weedy annual plantsK-selected: whales, wolves, elephants, primatesWhat about humans?+/- Population SizeEmigration—movement of individuals out of populationDispersalTake genes with them—protect species in case of catastropheFactors that Regulate GrowthIntrinsic—within organismExtrinsic—outside the populationBioticAbioticDensity-dependentDensity-independentDensity-independentAbiotic-weather, climateExtremes at wrong time of yearWithout regard to the number of organisms presentDensity-dependentDecrease natality, increase mortalityInteractions between populationsSome within populationInterspecific—predator-prey population levels, peaks and valleys slightly offsetCyclicalDensity-dependentIntraspecific—compete for resourcesAs carrying capacity is reached, resources are limitedFirst, quickest, clever, luckyTerritorialityFighting equipmentAttractiveness-song and danceDensity-dependentStress—”stress shock” causes physical and psychological and behavioral changesCombinations—OK food and water, space is lacking, lab animals, humans, chickensHumane livestock practices—not crowding chickens, livestock, “slow food” movementPopulation Size MaintenanceConservation biology: maintain populations for long term viabilityMaintain biodiversity:Number of species andGenetic variationEcosystem ChangeEcosystem ChangeLife constantly undergoing changeLife constantly undergoing changePopulations change or evolvePopulations change or evolveEcosystems evolve alsoEcosystems evolve alsoChange in populations size: population dynamics (more detail Change in populations size: population dynamics (more detail later)later)Changes may include increase and decreases in population sizeChanges may include increase and decreases in population sizeGrowth Curves Growth Curves Populations inherent ability to exponentially increase population Populations inherent ability to exponentially increase population sizesizeThey donThey don’’ttWhyWhyPopulations Populations Change in size (total number of individuals)Change in size (total number of individuals)Change in density (number of individuals in a certain space)Change in density (number of individuals in a certain space)Change in age distribution (proportion of individuals in each age Change in age distribution (proportion of individuals in each age group)group)Change in habitat distributionChange in habitat distributionClumpsClumpsResources may vary greatly from place to