Populations, Their changes and Their measurementIB syllabus: 2.1.6, 2.3.1, 2.3.2, 2.6.1-2.6.4, 2.7.2AP syllabusCh 9

Syllabus Statements2.1.6: Define the terms species, population, habitat, niche, community and ecosystem with reference to local examples2.3.1: Construct simple keys and use published keys for the identification of organisms2.3.2: Describe and evaluate methods for estimating abundance of organisms2.6.1: Explain the concepts of limiting factors and carrying capacity in the context of population growth2.6.2: Describe and explain s and J population curves2.6.3: Describe the role of density-dependent and density-independent factors and internal and external factors, in the regulation of population2.6.4: Describe the principles associated with survivorship curves including K and r-strategists2.7.2: Describe and evaluate methods for measuring change in abiotic and biotic components of an ecosystem due to a specific human activity

VocabularyAbiotic factorBiotic factorCarrying CapacityHabitatK-strategistPopulationr-strategist

PopulationA group of individuals of the same species found in the same area (habitat) at the same time

The gopher tortoises in scrub habitats in Volusia countyThe bottlenose dolphins of the Indian River Lagoon

Sea Otters: A case studySea otters keystone species in Pacific kelp forestsDaily consume 25% body weight in urchins & molluscsPopulation > 1 million before settlers arrived1700s hunted to near extinction 1000 in the Aleutians, AK only 20 off CaliforniaIn 1971 A-bomb test in AK used sea otter population to assess bombs power 1000s died 1973 Endangered Species Act passes, 1976 Marine Mammal Conservation Act1989 1000s died in Exxon Valdez Oil spillOtters recovering in most places after 1970sThe spring 2008 survey found 2760 sea otters, down 8.8-percent from the record 2007 spring survey.Why are they declining now?

New Threats?Pollution Effects - Shellfish magnify toxins - Reduce disease resistance - Reduce fertilityIncreased Predation - Killer Whales - Switch to otters when other food is scarce

Population characteristicsPopulations are dynamic change in response to environmentSize (# of individuals)Density (# of individuals in a certain space)Dispersion (spatial pattern of individuals)Random, Uniform, Clumped based on foodAge distribution (proportion of each age)Changes called Population dynamicsRespond to environmental stress & change

Clumped(elephants)Uniform(creosote bush)Random(dandelions)Common Dispersion PatternsClumped is most common because resources have a patchy distribution.

Limiting Factors & Population Growth4 variables govern changes in population sizeBirth, Death, Immigration, emigrationVariables are dependent on resource availability & environmental conditions

Population change = (Birth + Immigration) (Death + Emigration)

2004 Brooks/Cole Thomson Learning

Capacity for GrowthCapacity for growth = Biotic potentialRate at which a population grows with unlimited resources is intrinsic rate of increase (r)High (r) (1)reproduce early in life, (2)short generation time, (3)multiple reproductive events, (4)many offspring each timeBUT no population can grow indefinitelyAlways limits on population growth in nature

Carrying CapacityEnvironmental resistance = all factors which limit the growth of populationsPopulation size depends on interaction between biotic potential and environmental resistance

Carrying capacity (K) = # of individuals of a given population which can be sustained infinitely in a given area

Limiting FactorsCarrying capacity established by limited resources in the environmentOnly one resource needs to be limiting even if there is an over abundance of everything elseEx. Space, food, water, soil nutrients, sunlight, predators, competition, disease

A desert plant is limited byBirds nesting on an island are limited by

Minimum Values(r) depends on having a certain minimum population size MVP minimum viable pop.Below MVP1 some individuals may not find mates2 genetically related individuals reproduce producing weak or deformed offspring3 genetic diversity may drop too low to enable adaptation to environmental changes bottleneck effect

Forms of GrowthExponential growth starts slow and proceeds with increasing speed J curve resultsOccurs with few or no resource limitationsLogistic growth (1) exponential growth, (2) slower growth (3) then plateau at carrying capacity S curve resultsPopulation will fluctuate around carrying capacity

Time (t)Time (t)Population size (N)Population size (N)KExponential GrowthLogistic GrowthPopulation Growth Curves Ideal

Carrying capacity alterationsIn rapid growth population may overshoot carrying capacityConsumes resource baseReproduction must slow, Death must increaseLeads to crash or diebackCarrying capacity is not fixed, affected by:Seasonal changes, natural & human catastrophes, immigration & emigration

Density EffectsDensity Independent Factors: effects regardless of population densityMostly regulates r-strategistsFloods, fires, weather, habitat destruction, pollutionWeather is most important factor

Density EffectsDensity dependent Factors: effects based on amount of individuals in an areaOperate as negative feedback mechanisms leading to stability or regulation of populationExternal FactorsCompetition, predation, parasitismDisease most epidemics spread in cramped conditionsInternal FactorsReproductive effects Density dependent fertility, Breeding territory size

Natural Cycles: PredationOver longer time spans populations cycleCanadian lynx & Snowshoe hare - 10 year cycles Once thought that predators controlled prey #s Top down controlNow see a negative feedback mechanism in place community equilibrium

Population size (thousands)1601401201008060402001845185518651875188518951905191519251935YearHareLynx

5,0004,0003,0002,0001,000500Number of moose100908070605040302010019001910193019501970199020001999YearNumber of wolvesMoose populationWolf population

Reproduction Strategies effect SurvivalAsexual reproductionProduce clones of parentsCommon in constant environmentsSexual reproductionMating has costs time, injury, parental investment, genetic errorsImproves genetic diversity survive environmental changeDifferent male & female roles in parental care

MacArthur Wilson ModelsTwo idealized categories for reproductive patterns but really its a continuumr-selected & K-selected species depending on position on sigmoid population curver-selected species: (opportunists) reproduce early, many young few surviveCommon after disturbance, but poor competitorsK-selected species: (competitors) reproduce late, few young most surviveCommon in stable areas, strong competitors

Number of individualsCarrying capacityK species;experienceK selectionr species;experiencer selectionK

r-Selected SpeciescockroachdandelionMany small offspringLittle or no parental care and protection of offspringEarly reproductive ageMost offspring die before reaching reproductive ageSmall adultsAdapted to unstable climate and environmental conditionsHigh population growth rate (r)Population size fluctuates wildly above and below carrying capacity (K)Generalist nicheLow ability to competeEarly successional species

Fewer, larger offspringHigh parental care and protection of offspringLater reproductive ageMost offspring survive to reproductive ageLarger adultsAdapted to stable climate and environmental conditionsLower population growth rate (r)Population size fairly stable and usually close to carrying capacity (K)Specialist nicheHigh ability to competeLate successional specieselephantsaguaroK-Selected Species

r versus KMost organisms somewhere in the middleAgriculture crops = r-selected, livestock = K-selectedReproductive patterns give temporary advantageResource availability determines ultimate population size

Survivorship curvesDifferent life expectancies for different speciesSurvivorship curve: shows age structure of populationLate loss curve: K-selected species with few young cared for until reproductive ageEarly loss curve: r-selected species many die early but high survivorship after certain ageConstant loss curve: intermediate steady mortality

Humans Impact Natural PopulationsFragmenting & degrading habitatsSimplifying natural ecosystemsUsing or destroying world primary productivity which supports all consumersStrengthening pest and disease populationsEliminating predatorsIntroducing exotic speciesOverharvesting renewable resourcesInterfering with natural chemical cycling and energy flow

Physiological changesPsychological changesBehavior changesFewer or no offspringGenetic defectsBirth defectsCancersDeathOrganism LevelChange in population sizeChange in age structure (old, young, and weak may die)Survival of strains genetically resistant to stressLoss of genetic diversity and adaptabilityExtinctionPopulation LevelEcosystem LevelEnvironmental StressDisruption of biogeochemical cyclesHabitat loss & degradationLower species diversityLess complex food websLower stabilityEcosystem collapse

Sampling populations

Step 1: Identify the organismUse dichotomous keys, field guides, observe a museum collection, or consult an expert

http://www.earthlife.net/insects/orders-key.html#keySample key for insect IDhttp://people.virginia.edu/~sos-iwla/Stream-Study/Key/Key1.HTMLMacroinvertebrate key

Construct you Own Dichotomous Key

Mark & Recapture MethodUsed for fish & wildlife populationsTraps placed within boundaries of study areaCaptured animals are marked with tags, collars, bands or spots of dye & then immediately releasedAfter a few days or weeks, enough time for the marked animals to mix randomly with the others in the population, traps are set againThe proportion of marked (recaptured) animals in the second trapping is assumed equal to the proportion of marked animals in the whole populationRepeat the recapture as many times as possible to ensure accuracy of resultsMarking method should not affect the survival or fitness of the organism

Mark & Recapture Calculation # of recaptures in second catch = # marked in the first catch Total # in second catchTotal population (N)

Assuming no births, deaths, immigration, or emigration population size is estimated as follows (Lincoln Index)

N = (# marked in first catch) (Total # in second catch) # of Recaptures in second catch

MEMORIZE THIS EQUATION

Example50 snowshoe hares are captured in box traps, marked with ear tags and released. Two weeks later, 100 hares are captured and checked for ear tags. If 10 hares in the second catch are already marked (10%), provide an estimate of N

N = (50 hares x 100 hares) / 10 = 5000 / 10 = 500 hares**Realize for accuracy that you would recapture multiple times and take an average**

Quadrat MethodUsed for plants or sessile organismsMark out a gridline along two edges of an areaUse a calculator or tables to generate two random numbers to use as coordinates and place a quadrat on the ground with its corner at these coordinatesCount how many individuals of your study population are inside the quadratRepeat steps 2 & 3 as many times as possibleMeasure the total size of the area occupied by the population in square metersCalculate the mean number of plants per quadrat. Then calculate the population size with the following equation

Quadrat MethodN = (Mean # per quadrat) (total area) Area of each quadratThis estimates the population size in an area

Ex. If you count an average of 10 live oak trees per square hectare in a given area, and there are 100 square hectares in your area, then

N = (10 X 100 hectare2) / 1 hectare2 = 1000 trees in the 100 hectare2

In addition to population size we can measureDensity = # of individuals per unit areaGood measure of overall numbers

Frequency = the proportion of quadrats sampled that contain your speciesAssessment of patchiness of distribution

% Cover = space within the quadrat occupied by each speciesDistinguishes the larger and smaller species

How can changes in these populations be measured?Necessary because populations may change over time through processes like successionBut also because human activities may impact a population and we want to know howImpacts include toxins from mining, landfills, eutrophication, effluent, oil spills, overexploitation

Measuring changes cont.Can still use CMR or quadrat methodJust do it repeatedly over timeAlso could use satellite images taken over time

1. Do pre and post impact assessments in one area2. Measure comparable areas one impacted, one not at a given time

Overexploitation, Agricultural use, Global Warming haveCaused a decrease in Lake Chads area over last 50 years

LakeChadSatellite Images

Capture Mark - RecapturePractice Problems

In a mark recapture study of lake trout populations, 40 fish were captured, marked and released. In a second capture 45 fish were caught; 9 of these were marked. What is the estimated number of individuals in the lake trout populationQuestion 1

Question 2Woodlice are terrestrial crustaceans that live under logs and stones in damp soils. To assess the population of woodlice in an area, students collected as many of the animals as they could find, and marked each with a drop of fluorescent paint. A total of 303 were marked. 24 hours later, woodlice were collected again in the same place. This time 297 were found, of which 99 were seen to be already marked from the first time. What approximately, is the estimated population of woodlice in this area?

Review pointsDispersion patternsCarrying capacity and limiting factorsr and K selectionNatural population cyclesHuman effects

http://www.otterproject.org