2Population Dynamics and Carrying Capacity study of how populations change in size, density, and age distributionpopulations respond to their environmentchange according to distribution
3Dynamics of Natural Populations Population growth curvesBiotic potential - the ability to increase population numbersEnvironmental resistance - the combination of all the biotic and abiotic factors that limit a population’s increase.Carrying capacity – the upper limit to the population of any particular organism that an ecosystem can support
4Density Dependence And Critical Number Environmental resistance factors can be density dependent.If population density increases, environmental resistance becomes more intense and causes in increase in mortality.If population density decreases, environmental resistance lessens, allowing the population to recover.Food, Water, Disease, PredationEnvironmental factors that cause mortality can be density independentA sudden deep freeze in springA fire that may kill all small mammalsNatural Disasters
5Biotic Potential and Environmental Resistance Lack of food or nutrientsLack of waterLack of suitable habitatAdverse weatherPredatorsDiseaseParasitesCompetitorsBiotic PotentialReproductive rateAbility to migrate (animals) or disperse (seeds)Ability to invade new habitatsDefense mechanismsAbility to cope with adverse conditions
7Exponential and Logistic Growth - Rapid exp. growth followed by steady dec. in pop. Growth w/time until pop. Size levels offEXPONENTIAL GROWTHPopulation w/few resource limitations; grows at a fixed rate
10STABLEpop. Size fluctuates above or below its carrying capacityStable population sizeEX: undisturbed tropical rain forestsIRRUPTIVEpop. Growth occasionally explodes to a high peak then crashes to stable low levelEX: Algae, insectsCYCLICFluctuations occur in cycles over a regular time periodEX: Lynx & snowshoe hareIRREGULARNo recurring pattern in changes of population size
11The Role of Predation in Controlling Population Size Top-down control- lynx preying on hares periodically reduce the hare pop.Bottom-up control- the hare pop. may cause changes in lynx pop.
13How do Species Reproduce ASEXUAL REPRODUCTIONall offspring are exact genetic copies of a single parentCommon in single celled species (bacteria)Each cell divides to produce 2 identical cellsSEXUAL REPRODUCTIONOrganisms produce offspring by combining sex cells or gametes from both parentsProduces offspring with combination of genetic traits from each parentProvides greater genetic diversity in offspringDISADVANTAGESMales do not give birthIncreased chance of genetic errors and defectsCourtship & mating rituals consume time & energy and transmit diseases
14Reproductive Patterns and Survival OBJ 9.10Reproductive Patterns and Survivalr-selected species vs. K-selected speciesFig p. 170
15Survivorship CurvesShows the % of members in a pop. Surviving at different agesLATE LOSSHigh survivorship to certain age; then high mortalityEX: elephants, rhinos, humansCONSTANT LOSSFairly constant death rate at all agesEX: songbirdsEARLY LOSSSurvivorship is low early in lifeEX: annual plants, bony fish sp.
16Age Structure Stages PREREPRODUCTIVE AGE - Not mature enough to reproduceREPRODUCTIVE AGE- Capable of reproducingPOSTREPRODUCTIVE AGE- too old to reproduce
17Factors Governing Changes in Population Size Four variablesbirths, deaths, immigration and emigrationPopulation Change = (births + immigration) – (deaths + emigration)Crude Birth Rate = CBR = (births/population)*1000Crude Death Rate = CDR = (deaths/population) *1000Immigration and emigration are calculated the same wayCrude Growth Rate = CBR = CDRPopulation Growth Rate = CGR * 100
18Calculating Population Growth N0 is the starting populationN is the populationafter a certain time, t ,has elapsed,r is the rate of natural increase expressed as a percentage (birth rate - death rate) ande is the constant (the base of natural logarithms)
19Growth Curves – Two Types J or S Exponential growth results in population explosionRule of 70to find the doubling time of a quantity growing at a given annual percentage rate, divide the percentage number into 70 to obtain the approximate number of years required to double.For example, at a 10% annual growth rate, doubling time is 70 / 10 = 7 years.This results in a J curve graph.