Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Chapter 26Population Growth and Regulation12EcologyEcology – the study of the interrelationships of organisms with each other and with their non-living enviornmentWhat factors effect population size?Populations change through births, deaths, or migration•Immigration – migration into the population•Emigration – migration out of the population26.1326.1How Does Population Size Change?In most natural populations birth and death rates are the primary factors that influence population size26.1426.1How Does Population Size Change?Two major opposing factors determine birth and death rates:•Biotic potential – the theoretical maximum rate at which a population could increase•Assumes ideal conditions for maximum birth and minimum death•Environmental resistance – curbs on population growth set by the living and nonliving enviornment5How Does Population Size Change?Biotic potential is influenced by several factors:1. The age of reproductive maturity2. The frequency of reproduction3. The average number of offspring4. The length of reproductive lifespan5. The death rate under ideal conditions26.1626.1Biotic potential vs environmental resistanceExponential growth – a pattern of continuous increase in population sizeIf births exceed deaths by a constantPercentage you get a j curve26.2726.1Biotic potential vs environmental resistanceThe effect of death rateAssumes bacterial population doubles every 20 min26.38How is population growth regulated?Population growth cannot continue indefinitely!!In other words exponential growth is only possible under certain conditions•Boom and bust cycles•When environmental resistance is reduced26.2926.2Boom-and-bust cyclesFig 26.410Boom-and-bust cycles26.2Fig 26.411When environmental resistance is reduced you can also see periods of exponential growth•Increased food•Elimination ofpredatorsThe whooping crane was protected in 194026.2Fig 26.512Environmental resistance limits population growthLogistic population growth•Result of environmental resistance•Characterized by an S-curveCarrying capacity – the maximum population size that can be sustained by an ecosystem for an extended period without damage to the eco system26.213Logistic population growth26.2Fig 26.614Logistic population curve in natureOcean currents carry barnacle larvae to rocky seashoresEventuallycompetition for space limits population growth26.2Fig 26.815What if a population exceeds its carrying capacity?26.216What if a population exceeds its carrying capacity?26.2Fig 26.617What if a population exceeds its carrying capacity?Ex: Reindeer introduced onto an island with no large predators26.2Fig 26.718Environmental resistance usually maintains populations at or below their carrying capacityFactors that generate environmental resistance fall into two categories1. Density-independent factors2. Density-dependent factors26.219Density-independent factorsFactors that limit populations regardless of the population density•Weather and climate•Responsible for most boom-and-bust population cycles•Habitat destruction by humans26.220Density-dependent factorsFactors that become more effective as the population density increases•Predators•Parasites•Competition for resources26.221Density-dependent factors: predatorsPredators are organisms that eat other organisms (prey)Predator/prey relationships can result in out-of-phase population cycles26.2 Fig 26.1122Density-dependent factors: parasitesParasites •Feed on a larger “host” animal causing harm•Spread more rapidly among dense populations•Weaken their host making them susceptible to death and less likely to reproduce26.223Density-dependent factors: Competition for resourcesInterspecific competition – competition among individuals of different speciesIntraspecific competition – competition among individuals of the same species26.224Density-dependent factors: Competition for resourcesIntraspecific competition• scramble competition26.2Fig 26.1225So how are populations distributed?Ecologists recognize three major types of spatial distribution26.3Fig 26.1426How is the human population changing?26.4Fig
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