Ecology Ecology Lecture 7 Lecture 7 Ralph Kirby Ralph Kirby
Dec 19, 2015
Population (Ecology)Population (Ecology)– Group of individuals of the same Group of individuals of the same
species inhabiting the same areaspecies inhabiting the same areaInterbreeding if sexualInterbreeding if sexualLimited in spaceLimited in space
Populations havePopulations have– DensityDensity– Distribution in timeDistribution in time– Distribution in spaceDistribution in space
These are defined byThese are defined by– Rate of birthRate of birth– Rate of growthRate of growth– Rate of deathRate of death
Resulting in age & sex structureResulting in age & sex structure
What is an individual– Easy for most large
sexually reproducing animals
– Not so easy for colonies of animals and many plants
– Ants– Bees– Coral– Trees (Ramets)– Fungi
DistributionDistribution– Area over which a Area over which a
species occursspecies occurs
AbundanceAbundance– Numbers of that Numbers of that
species present in species present in the areathe area
Both vary by Both vary by available habitatavailable habitat– TemperatureTemperature
Red MapleRed Maple– -40-40ooCC
Carolina wrenCarolina wren– Northwards -7Northwards -7ooCC– Westward>52mmWestward>52mm
– When all When all environmental environmental factors within its factors within its range of tolerance, range of tolerance, the organism can the organism can live in its habitatlive in its habitat
Horned larkHorned lark– Avoids forestsAvoids forests– Available Available
territoryterritory
Density can be a key factorDensity can be a key factor– Number of individuals per unit spaceNumber of individuals per unit space– AffectsAffects
growth rategrowth rateResourcesResourcesMatesMatespredationpredation
Thus density controls in partThus density controls in part– Birth rateBirth rate– Growth rateGrowth rate– Death rateDeath rate
Density is difficult to define or measureDensity is difficult to define or measure– What area do you useWhat area do you use– What distribution has the species within the What distribution has the species within the
areaarea– How do you measure the densityHow do you measure the density– Ecological densityEcological density
Some use a factor associated with the habitatSome use a factor associated with the habitat
Distribution Distribution – ClumpedClumped
NormalNormal– UniformUniform
High density and competitionHigh density and competition– RandomRandom
Social behaviorSocial behaviorAvailable nesting sitesAvailable nesting sites
MetapopulationMetapopulation– Multi-Habitat based multiple populationsMulti-Habitat based multiple populations
How do you countHow do you countDirect CountsDirect Counts– Time consumingTime consuming– Needs to be sure you can see all individuals in the areaNeeds to be sure you can see all individuals in the area
QuadratsQuadrats– Organisms must be staticOrganisms must be static– Needs laying of quadrats to be randomNeeds laying of quadrats to be random– Statistical analysis essentialStatistical analysis essential
Mark and recaptureMark and recapture– EstimateEstimate
Assumes equal chance of capture for allAssumes equal chance of capture for allNo deaths or birthsNo deaths or birthsMarked animals random among unmarkedMarked animals random among unmarkedNo loss of marksNo loss of marksNo emigration or immigrationNo emigration or immigrationOther factors include time of capture, stress of capture, sex, age, etc.Other factors include time of capture, stress of capture, sex, age, etc.
Relative abundanceRelative abundance– Using a factor such as tracks, bird song, etcUsing a factor such as tracks, bird song, etc– Get a relative measureGet a relative measure
Disperal – Active and PassiveDisperal – Active and PassiveEmigration – Escaping high densityEmigration – Escaping high densityImmigration – Moving into empty habitatImmigration – Moving into empty habitatMigation – A round trip, perhaps involving matingMigation – A round trip, perhaps involving mating
Age structureAge structure– PrereproductivePrereproductive– ReproductiveReproductive– PostreproductivePostreproductive– Short life spanShort life span
Rapid increaseRapid increase
– Long Life spanLong Life spanSlow increaseSlow increase
Measuring Age Measuring Age structurestructure– Mark and recaptureMark and recapture
Accurate but hard Accurate but hard to doto do
– Special featuresSpecial featuresTeethTeethHorn ringsHorn ringsTree ringsTree rings
Age PyramidsAge Pyramids– Show status of Show status of
populationpopulation
Size/Age can affect the Size/Age can affect the population structurepopulation structure
Sex ratios in populations Sex ratios in populations shifts with ageshifts with age– HumansHumans
More malesMore males
Males have shorter life spanMales have shorter life span– WarWar
– High risk activitiesHigh risk activities
Females need to survive giving Females need to survive giving birth to childrenbirth to children
Therefore sex ratios have Therefore sex ratios have change a lot over the last two change a lot over the last two hundred yearshundred years
– Parturition fever in 19Parturition fever in 19thth Century Century
– First World War in UKFirst World War in UK
– Second World War in USSRSecond World War in USSR
Plants are more Plants are more difficultdifficult– Hard to detrmine Hard to detrmine
ageage– Extremely high Extremely high
loss fo seedlingsloss fo seedlings– Use of yield tableUse of yield table
Probability of survival is age specificProbability of survival is age specific– See death tableSee death table– Probability of death in next yearProbability of death in next year
Life TableLife Table– nnxx
Number in cohortNumber in cohort
– llxxProbability of surviving from birthProbability of surviving from birth
– qqxx
Age specific mortalityAge specific mortality
BirthrateBirthrate– Sex specificSex specific– Age specificAge specific
Net reproductive rate Net reproductive rate depends ondepends on– FecundityFecundity– SurvivorshipSurvivorship
GivenGiven– Age specific mortalityAge specific mortality– Age specific birth rateAge specific birth rate– Project population Project population
growth/declinegrowth/decline
Exponential GrowthExponential Growth– Depends on rate of Depends on rate of
reproduction, reproduction, λλ– If If λλ less than 1, there less than 1, there
is clineis cline
Population growth is Population growth is limited by the limited by the environmentenvironment– Carrying CapacityCarrying Capacity– See reindeerSee reindeer
NonconformityNonconformity– Change in age Change in age
structurestructure– ImmigrationImmigration– EmigrationEmigration– Changes in birth and Changes in birth and
death ratesdeath ratesBut stable once it But stable once it reaches carrying reaches carrying capacitycapacity
Populations should work via positive and negative feedbacksPopulations should work via positive and negative feedbacksDoes not work smoothlyDoes not work smoothly– Depends on environment such as overgrazingDepends on environment such as overgrazing
Population cycles in simpler systemsPopulation cycles in simpler systems– Food availabilityFood availability
Can result in extinctionsCan result in extinctions– Two typesTwo types
Change in environment. Start locallyChange in environment. Start locallyMass extinctions. External event?Mass extinctions. External event?
Three Models for regulation of Three Models for regulation of population densitypopulation densityK represents equilibriumK represents equilibrium– Partial density regulation APartial density regulation A
Birth Rate (B) independent of Birth Rate (B) independent of population densitypopulation densityMortality Rate (M) increases with Mortality Rate (M) increases with densitydensity
– Partial density regulation BPartial density regulation B Birth Rate (B) declines with population Birth Rate (B) declines with population densitydensityMortality Rate (M) independent of Mortality Rate (M) independent of population densitypopulation density
– Full density dependent regulationFull density dependent regulationBirth Rate (B) increases with Birth Rate (B) increases with deceasing population densitydeceasing population densityMortality Rate (M) increases with Mortality Rate (M) increases with increasing population densityincreasing population density
Carrying capacityCarrying capacitySee effect of density for See effect of density for tadpoles and white clovertadpoles and white clover– Maximum number of sustainable Maximum number of sustainable
individualsindividuals– Results in intra-specific Results in intra-specific
competitioncompetition– Two typesTwo types
Scramble competitionScramble competition– Growth and reproduction depressed Growth and reproduction depressed
for all individualsfor all individualsCan result in local extinction or Can result in local extinction or population crashpopulation crash
Contest competitionContest competition– Some individual deny resources to Some individual deny resources to
other individuals resulting in some other individuals resulting in some growing and reproducing better than growing and reproducing better than othersothers
Indirect via exploitation of Indirect via exploitation of resourcesresourcesDirect via interferenceDirect via interference
Population crash Population crash caused by caused by RindepestRindepest
Note exponential Note exponential increase from low increase from low basebase
Grass limited in dry Grass limited in dry seasonseason
Competition related Competition related to rainfall producing to rainfall producing grassgrass
Once in equilibrium, Once in equilibrium, rainfall most rainfall most importantimportant
Effect of Effect of repottingrepottingEffects can Effects can differdiffer– Bison is Bison is
exponentiaexponential curvel curve
– Grizzly Grizzly bear is bear is linear linear effecteffect
Competition Competition can affect can affect reproductionreproduction– harp sealsharp seals
IncreasIncreased age ed age of of sexual sexual maturitymaturity
– maizemaizeLinearLinear
– marsh marsh herbherb
Effects of high density on Effects of high density on reproductionreproduction
StressStressPheromonesPheromonesDiseaseDiseaseIncreased mortality of youngIncreased mortality of youngResults in dispersalResults in dispersal– Sources HabitatSources Habitat– Sink HabitatSink Habitat
Can be dangerousCan be dangerousLack protective coverLack protective coverHigh number of predatorsHigh number of predators
– Move no further than necessaryMove no further than necessary– Move in foraysMove in forays
Social dominance can affect reproduction and dispersionSocial dominance can affect reproduction and dispersionFighting and social position. Both male and female hierarchies are possibleFighting and social position. Both male and female hierarchies are possibleResults in limited matingResults in limited mating– AlphaAlpha– BetaBeta– OmegaOmega
Home RangeCan overlap
TerritoryNo overlapFight to protect
Dominant male getsbest locations
Males and femaleranges can differ
Male and femaleranges overlap
Territory is protectedTerritory is protected– FoodFood– MatingMating– Nesting siteNesting site– Attraction of matesAttraction of mates– Avoidance of suboptimal habitatAvoidance of suboptimal habitat– Needs energyNeeds energy
May not be optimal strategy when May not be optimal strategy when resources are lowresources are low