Presentation on theme: "Population Ecology Population ecology is the study of populations in relation to environment Including environmental influences on population density and."— Presentation transcript:
1Population EcologyPopulation ecology is the study of populations in relation to environmentIncluding environmental influences on population density and distribution, age structure, and variations in population size
2Levels of Organization OrganismPopulationCommunityEcosystemBiome
4Size: total # of individuals in a pop (N) Density: # / unit area Describing populationsSize: total # of individuals in a pop (N)Density: # / unit area
5Estimation of Population Size Describing populationsEstimation of Population SizeSampling techniqueMark and recapture
6Mark and Recapture Orgs are captured, tagged, and then released. Describing populationsMark and RecaptureOrgs are captured, tagged, and then released.Some time later, the same process is repeated and the following is used:
7Describing populations Ex:Suppose that 50 zebra mussels are captured, marked, and released. One week later, 100 zebra mussels are captured and 10 are found to have markings already. The estimated population would then beN= (50·100) / (10) = 5000/10 = 500N=500
8Dispersion Clumped Uniform Random Describing populationsDescribes how individuals in a population are distributedClumpedUniformRandom
9Fish travel in schools – safety in numbers Clumped dispersion (most common)Individuals aggregate in patchesMay be influenced by resource availability & behaviorDescribing populationsExample:For many animals, such as these wolves, living in groupsincreases the effectiveness of hunting.spreads the work of protecting and caring for young.helps exclude other individuals from their territory.Fish travel in schools – safety in numbers
10Some plants secrete toxins that keep others away Uniform dispersion-Individuals are evenly distributed-May be influenced by social interactions such as territorialityDescribing populationsBirds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.Some plants secrete toxins that keep others away
11Random dispersionThe position of each individual is independent of other individualsDescribing populationsDandelions grow from windblown seeds that land at random and later germinate.
12Changes in Population Size Describing populationsChanges in Population SizeBiotic potential of a population=max rate at which a population could increase under ideal conditionsInfluenced by several factors:Age at which reproduction beginsLife span during which the organisms are capable of reproducingNumber of reproductive periods in the lifetimeNumber of offspring the organism is capable of having
13Age StructureDescribing populationsDescription of the abundance of individuals of each age in a population.
20Survivorship CurvesDescribing populationsDescribes how the mortality of individuals in a species varies during their lifetime1000100101Number of survivors (log scale)2468Age (years)MalesFemalesThe survivorship curve for Belding’s ground squirrelsShows that the death rate is relatively constant
21A species in which most survive to middle age Survivorship curves can be classified into three general types: Type I, Type II, and Type IIIIIIIII501001101,000Percentage of maximum life spanNumber of survivors (log scale)Type IA species in which most survive to middle ageParentingType IILength of survivorship is random. Death rate is constant.
22Animation Most individuals die young. Few reach reproductive maturity. Type IIIMost individuals die young.Few reach reproductive maturity.Fish release 1000s of eggs.No parentingIIIIII501001101,000Percentage of maximum life spanNumber of survivors (log scale)Animation
24Factors Affecting Population Limiting FactorsFactors Affecting PopulationThings that prevent a population from attaining its biotic potential2 categoriesDensity-dependentDensity-independentDensity DependentDensity Independent
25Factors Affecting Population Density DependentFactors Affecting PopulationPopulations regulated by density-dependent factors are affected by the number of organisms present.PredationParasitismDiseaseCompetition-the more organisms crowd together, the more damaging are food shortages, parasites, and predators.Intraspecific Competition = the struggle between members of a population for scarce resources
26Factors Affecting Population Density IndependentFactors Affecting PopulationThe number of organisms present does not affect the influence of the factor.Fire, earthquakes, storms, floodsDensity-independent factors show no correlation with the size of the population.
27Describing Population Growth Population ecologists describe two general patterns of populations growth:ExponentialLogistic
28Types of Population Growth The growth of a population can be described by the following equation:r= reproductive rate (or growth rate)N= population size at the beginning of the interval for which the births and deaths are counted.r =.Types of Population GrowthNet increase of individualsbirths-deathsNCan r be negative? Zero?
29Types of Population Growth births-deathsNEx:A population of 1000 had 60 births and 10 deaths over a one year period. What is the growth rate?0.05 per year
30Types of Population Growth Exponential growthr>0Types of Population GrowthIn a population showing exponential growth the individuals are not limited by food, disease, predation or competition.If the rate of reproduction per individual remains constant through time, then the rate at which the population increases is a multiple of the number of individuals in the population.
31Types of Population Growth Exponential population growthResults in a J-shaped curveUsually short lived in nature- not sustainabler>0Types of Population Growth510155001,0001,5002,000Number of generationsPopulation size (N)dNdt1.0N0.5NPopulation size (N)
32Types of Population Growth the real worldCarrying Capacity (K)Types of Population GrowthPopulations usually reach a carrying capacity.Upper limit to the number of individuals the environment can support.
33Types of Population Growth Logistic growthdNdtrmaxNTypes of Population GrowthIn most real populations both food and disease become important as conditions become crowded.A population can grow exponentially only for short periods of time, because it would very quickly deplete all the resources necessary for its survival.Over long periods of time, populations tend to attain an equilibrium population size which is determined by the available resources.Animation
34Types of Population Growth Zero population growthOccurs when the birth rate equals the death rateThe population growth equation can be expressed asdNdtrN
35Life-history strategies Logistic and exponential growth are associated with 2 kinds of life-history strategiesR-selected species (strategists)organisms are opportunistic; they reproduce rapidly when the environment is uncrowned and resources are vastK-selected species (strategists)operate at a density near K
36Life-history strategies R-selected speciesLife-history strategiesa. Opportunistic species, which tend to be colonizers.b. Grasses, many insects-Usually quickly invade, reproduce many offspring and die-Offspring mature quickly and require very little parental carec. Strategies for continued existence is based on individuals having the following traits: 1) small size 2) short life span 3) mature fast 4) produce many offspring 5) engage in little care of offspring
37Life-history strategies K-selected speciesLife-history strategiessensitive to population densitySuch populations are equilibrium species, tend to be specialists rather than colonizers, and may become extinct when their evolved way of life is disrupted (e.g., the grizzly bear, Florida panther, etc.).Overall strategy for continued existence is based on having the following traits: 1) large size 2) long life span 3) slow to mature 4) produce few offspring 5) expend considerable energy in care
39Human Population Growth The following made exponential growth possibleIncreases food supplyReduction in diseaseReduction in human wasteExpansion of habitatAs of 28 April 2010, the human population of the world is estimated by the United States Census Bureau to be 6,817,500,000.