Ecology - the study of the relations between organisms and theirenvironment (both biological and physical)Population Ecology - the study of the factors that influence thenumbers and distribution of a speciespopulation - a group of individuals of the same species livingin an areaSome species havelimiteddistributionsPopulation sizehas an importantinfluence onspecies persistencePopulations often change distributions through time due toclimate changeSome species have increased their range due to chanceintroductionsPopulation DispersionRandom distributions result whenindividuals of a species do not interactwith each other positively ornegatively - rare in natureUniform distributions result fromcompetition for resources orbehavioral interactions liketerritorialityClumped distributions often resultfrom an uneven distribution ofrequired resources or socialinteractions like herdingMetapopulations - distinct populations that interact with each otherthrough dispersal - allow greater overall numbers and persistentrefuges that can be a source of species recolonization of an areaafter local extinctionWith increasing human impact onhabitats and the range of manyspecies - the study of thedynamics of metapopulations hasimportant implications for thelong-term conservation of somespeciesDemography - the study of population parameters and statisticsCan help to predict population changePresent distribution of ages, distribution of sexes, survival rates,birth rates all have effects on the characteristics of the populationin the futureFactors that influence population changesex ratio - birth rate is most closely related to number offemales in the populationgeneration time - the average amount of time that it takes fora female to give birth to another female - shorter generationtimes can lead to faster population growthage structure - the number of individuals in each age class -number of individuals of reproductive age can influencepopulation growthPopulations maintain stable numbers when the number of birthsin each time period is matched by the number of deathsSurvivorship - the proportion of newborn individuals thatsurvive to a given age - if 50% survive to age 10, then age 10survivorship is 0.5Survivorship curve - showschanges in mortality ratethrough the life of a groupof individualsType I - most mortalitylate in lifeType II - uniformmortality throughout lifeType III - most mortalityearly in lifeReproduction has a price - reduced survival and/or reduced futurereproduction - “Cost of reproduction”There is a trade-off between the number of offspring producedand the investment in each offspringInvestment each offspring receives influences its chance ofsurvival - large clutches can result in few surviving offspring,small clutches also have few survivors, intermediate sizeclutches may produce the greatest number of survivors - the“optimal clutch size”Number of reproductive attempts per lifetimeIteroparous - having many attempts at reproduction - requireslow expenditure each time in order to ensure parental survivalSemelparous - having a single reproduction - maximalreproductive expenditure - “big bang” reproduction - seen wherechance of parental survival is low regardless of expenditure -annual plants in the desert, Pacific salmonAge at first reproduction is earlier in species that have lowsurvival rates - high survival rates often allow species to delayreproduction to gain experience and resourcesThe rate of population growth and the size of a population islimited by the environmentThe potential growth of populations is large - but most populationsmaintain relatively stable numbersTwo models of population growthExponential growth - the rate of change in population size is proportional to the number of individuals in the population and the intrinsic rate of increaseLogistic growth - the rate of change in the population is negatively impacted by an increase in the number of individuals in the population - density dependent growthExponential growth - the rate of change in population size isproportional to the number of individuals in the population andintrinsic rate of increasedN/dt = rNdN/dt - change in numbers per unit timeN - population sizer - intrinsic rate of increaser = birth rate - death rateLogistic growth - the rate of change in the population is negativelyimpacted by the number of individuals in the population - densitydependent growthdN/dt = rN(K-N)/KdN/dt - change in numbers per unit timeN - population sizer - intrinsic rate of increaser = birth rate - death rateK - the carrying capacityK - the number ofindividuals that a givenarea can supportindefinitelywhen N=K, dN/dt = 0Examples of Logistic GrowthLogistic growth is also called“density dependent” growthHigh density populations havefewer resources availablewhich leads to higher mortalityand lower birth rateshigh mortality and lower birthrates reduce dN/dt as thepopulation approaches itscarrying capacityThe growth rate of many populations is influenced byenvironmental factors that act independent of density - floods,freezes, storms, droughts, and other disasters - environmentalcontrols of population size often results in population “crashes.”The effect of unchecked population growthOther factors can lead to population cyclesPrey numbers can vary because of predator densityPredator numbers can vary because of prey densityPopulations that are routinely grow and decline due to densityindependent factors and those that grow in a density dependentfashion have very different adaptations that promote growth andreproduction under those conditionsPopulations that routinely grow in a density independent fashionhave adaptations that favor their ability to reproduce rapidly insize before the next population disaster. Such populations arecalled “r-selected” because they have characteristics that resultin a high instrinsic rate of increase.Populations that routinely grow in a density dependent fashionhave adaptations that favor their ability to survive and reproducewhen the population is at its carrying capacity. Such populationsare called “K-selected” because they have characteristics thatallow them to live in situations where resources are limited - attheir carrying capacity.Adaptations to density independent and density dependent growthThe human species exhibits many K-selected traits - likely due anancestry of species that lived at or near K - limited by foodavailability, predators, and diseaseTechnological advances