2 Introduction & Review Population Population Ecology Group consisting of members of the same species that live together in a prescribed area at the same time.Population EcologyThe study of numbers of individuals of a particular species, at a given time and location, and the interactions of that population with other populations and the environmentPopulation dynamicsStudy of changes in populations
3 Important Features of Populations Population EcologyImportant Features of Populations
4 Population Density Population Density This is how population size is expressedThe number of individuals of a species per unit space
5 Dispersion Dispersion Describes the spacing of individuals and there are three types.
6 Types of Dispersion Uniform Dispersion Clumped (Aggregated) Dispersion Individuals are evenly distributedClumped (Aggregated) DispersionMost common typeIndividuals are concentrated in specific parts of the habitatPatchinessOccurs as a result of distribution of resources or by asexual reproductionRandom dispersionOccurs when individuals of a population are spaced throughout an area in a manner that is unrelated to the presence of othersLeast common; hardest to observeResults from a lack of interaction between individuals or a homogenous environment
8 Equation ∆N/∆t = b – d r = b – d ∆N is the change in numbers in the population∆t is the change in timeb is the natality (birth) rated is the mortality rater = b – dr is the growth rate of the populationIf r is 0, the population is stableIf r > 1, the population is increasing in sizeIf r < 1, the population is decliningThese equations can be expressed as dN/dt = rNN is the population sizeRepresents arithmetic growthPopulation increases by the same amount over each interval of timeBubble Demonstration
10 Exponential Growth Exponential Growth Population growth is at a rapid paceReflects the maximum intrinsic rate of growthMaximum rate of growth under ideal conditions for that populationdN/dt = rmaxNrmax represents the maximum growth rateThis type of growth may exist for a period of time until limiting factors become importantHumans have exhibited this growth pattern for centuries—but can it last?
11 Exponential Growth & The Human Population I Thomas Malthus recognized that the human population cannot continue in exponential growthThere has been a large decrease in death rate and the population continues to increase to unknown proportionsNo one knows the carrying capacity of humans.Human growth rate will continue to increase until humans hit carrying capacityNot all countries have the same growth rateGrowth rate is higher in developing countriesAfrica and Southeast Asia countriesDoubling time is the time needed for a population to double in sizeReplacement-level fertility is the number of children a couple must have to replace themselves2.1 developed countries; 2.7 developing countriesTotal fertility rateAverage number of children born to a woman during her lifetimeAge structure of country can be used to predict future population growthBroader base shows growing populationNarrower base shows shrinking populationEnvironmental degradation is related to population growth and resource consumptionDeveloped countries require more resources per capitaCause more environmental problemsPeople overpopulation, too many people living in certain areas result in people over-utilizing resources
12 Exponential Growth & The Human Population II Not all countries have the same growth rateHigher in developing countriesIndiaSouth AsiaAfricaAge structure of a country can be used to predict future population growthShows the percentages of population at different agesA broader base to the age structure indicates a growing population while a narrower base indicates a stable or shrinking population.Human growth rate will continue to increase until humans hit carrying capacityNot all countries have the same growth rateGrowth rate is higher in developing countriesAfrica and Southeast Asia countriesDoubling time is the time needed for a population to double in sizeReplacement-level fertility is the number of children a couple must have to replace themselves2.1 developed countries; 2.7 developing countriesTotal fertility rateAverage number of children born to a woman during her lifetimeAge structure of country can be used to predict future population growthBroader base shows growing populationNarrower base shows shrinking populationEnvironmental degradation is related to population growth and resource consumptionDeveloped countries require more resources per capitaCause more environmental problemsPeople overpopulation, too many people living in certain areas result in people over-utilizing resources
13 Logistic Growth Logistic Growth Exponential growth with environmental resistance (carry capacity of the environment = K) incorporated into the equationdN/dt = rmaxN((K – N) /K)N = population sizeK = carrying capacityMaximum number of organisms that the environment can sustain indefinitely.Exhibited by most natural populations.
14 Potential Examination Question Logistic Growth Populations do not always approach and stabilize at K, but may overshoot K, followed by a population crash.Why does this occur?Provide an example.What reproductive strategies would be advantageous at high population densities (At or close to K)?What reproductive strategies would be advantageous at low population densities?Highability to reproduce with few resourcesability to compete well for limited resourcesability to use resources very efficientlyorganisms showing this type of strategy are sometimes called "K-selected", or equilibrialmost likely to be found in stable habitats where population size does not vary much once it has approached K.Lowearly sexual maturityshort generation timeincreased fecundityorganisms showing this type of strategy are sometimes called "r-selected", or opportunisticmost likely to be found in unstable habitats where environmental fluctuations result in large die-offs, or in newly colonized habitats where resources are not a limiting factor
15 Factors Influencing Population Size Population EcologyFactors Influencing Population Size
16 Dispersal Dispersal Movement of individuals among populations ImmigrationMigration of individuals into the populationEmigrationMigration of individuals out of the populationIf incorporated into the growth rate mathematical equationr = (b – d) + (i – e)
17 Density Dependent Factors Regulate population size and is difficult to access in nature and are limiting factors that increase in intensity as population size increases
18 Density Dependent Factors II PredationDiseaseIncreases when contact with toxic waste, produced by population itself, increases with population size.CompetitionIntraspecificCompetition between members of the same speciesInterspecificCompetition between members of different species
19 Density Independent Factors Limit population size and are factors that do not increase in intensity as the population size increases.Most density-independent factors have some relationship to population density.Many climatic factors are density-independent.
20 Density Independent Factors Climatic factorsSunlightRainfallTemperatureAll have impacts no matter what the population sizeClimatic and seasonal factors, monsoon season for example, can severely decrease populations
21 Life “History” Traits of Populations Population EcologyLife “History” Traits of Populations
22 IntroductionLife history traits, products of natural selection, are traits that affect an organism’s schedule of reproduction and survival.Birth Reproduction Death
23 Semelparous vs. Iteroparous Species Semelparous SpeciesExpend their energy in a single, immense reproductive effortPacific salmonAgaveIteroparous SpeciesExhibit repeated reproductive cyclesMost vertebratesMost shrubsMost trees
24 r Strategists r strategists Have traits that contribute to a high population growth rate.High rSmall sizeLarge numbers of offspringMay live in unpredictable habitatsWeedsPestsRoaches
25 K Strategists K strategists Maximize the chance of surviving in an environment where the number of individuals (N) is near the carrying capacity (K) of the environment.Population size near KLarger body sizeLong life spanLate reproduction and slow developmentHave fewer offspringMay care for their youngAfrican elephantsHumans
26 Survivorship Survivorship is related to r and k selection Type I SurvivorshipTypical of K-selected organismsHigh mortality rate later in lifeType II SurvivorshipCharacterized by constant mortality rate over timeBirds and lizardsType III Survivorshipr selected organisms.Characterized by high mortality rate early in life