CES 210 1st Edition Lecture 8Environmental Population DynamicsPopulation: group of individuals (all members of a single species) who live together in the same habitat and likely to interbreed- Unique physical distribution and space- Different ages, sizes, changing with timePopulation Dynamics: study of how, when and why?Primary Factors that Affect GrowthFour primary factors affect growth rate: Immigration, deaths, and emigration (r=B+I-D-E)Births: the number of births that occur in the population at any given time; rate of birthsvary by species and also with stress and food availabilityImmigration: the number of organisms that move into the population from another populationDeaths: mortality, or the number of deaths that occur in the population at any given time, vary by species and with environmental factorsEmigration: the number of organisms that move out of the population to another populationSecondary Factors Affecting Population DensitySecondary ecological events: other factors that affect population densityDensity-Independent: weather climate affect all equally and not dependent on overall population densityDensity-dependent: as a result of population density- The greater the population growth rate the faster a population grows- Growth is determined by knowing the population size now, at time tDescribing Population Growth MathematicallyPopulation: total number of all the members of a single species living in a specific area atthe same timeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Rate: this is the rate of growth; the number of individuals which can be produced per unit of time under ideal conditions (with no limits to the populations growth)Time: this is the unit of time upon which the rate is basedGeometric Rate of Increase: the population size that would occur after a certain amount of time under ideal conditions is described by the formula: Nt=N0rtExponential Growth Describes Continuous ChangeSuch change can be described by modifying the previous formula to: dN/dt=rNThe d is for delta that represents change Thus the formula would read: the change in the population (dN) per change in time (dt) is equal to the rate of change (r) times the population size (N)- Exponential growth only can be maintained by a population as long as nothing limits its growth- In the real world there are limits to growth that each population will encounter- Eventually shortages of food or other resources lead to a reduction in the population sizePopulation TerminologyCarrying Capacity: (k) the population of a species can be supported in a specific area without depleting the available resourcesOvershoot: when a population exceeds the carrying capacity of the environment and deaths result from scarcity of resourcesPopulation crash: a rapid dieback in the population to a level below the carrying capacityBoom and Bust: when a population undergoes repeated cycles of overshoots followed by crashesResource Scarcity Slows Exponential GrowthSometimes population growth slows down as resources become scarce and a populationnears its carrying capacityS-Shaped or Sigmoidal: slowing rate of growth results that shows a curve in a graphLogisitc Growth: is also another reference to the S-Shape and is shown mathematically as: dN/dt=r N (1-N/K)Factors Affecting Population growthLogisitics growth: is density dependent which means that the growth rate depends on the population density- Many density dependent factors can influence a population including: disease, physiological stress and predation- Density dependent factors intensify as population size increases- Density independent factors may also affect populations. These may include drought, fire or other habitat destruction that affects an ecosystemR and K selected Speciesr-selected species: rely upon a high reproductive rate to overcome the high mortality of offspring with little or no parental care. Ex: a clam can release a million eggs in a lifetime, with few surviving to maturityK-selected species: have few offspring, slower growth as they near carrying capacity and exercise more parental care. Ex: an elephant produces one offspring ever 4 to 5 years, but nurturing a herd increases the likelihood of it surviving maturityLife span varies by speciesMaximum Life Span: the longest period of life reached by a given type of organism- Bristlecone pines can live up to 4,600 years- Humans may live up to 120 years- Microbes may live only a few hoursDifferences in relative longevity among species shown as survivorship curvesSurvivorship curves vary by species Full physiological life span if organism survives childhood- Ex: elephants and bears Probability of death unrelated to age- Ex: gulls and mice Mortality peaks early in life- Ex: trees and fishFactors that regulate population growthIntrinsic factors: operate within or between individual organisms in the same speciesExtrinsic factors: imposed from outside the populationBiotic factors: caused by living organisms that tend to be density dependentAbiotic factors: caused by non-living environmental components. Tend to be density independent and do not really regulate population, although they may be important in increasing or decreasing numbers. Ex: Rainfall, stormsDensity dependent factorsReduce population size by decreasing natality or increasing mortalityInterspecific interactions (between species) - Predator- prey oscillationsDensity Dependent FactorsIntraspecific interactions: competition for resources by individuals within a population- As population density approaches the carrying capacity, one or more resources becomes limiting - Control of access to resources by territoriality; owners of territory defend it and its resources against rivalsStress-related diseases: occur in some species when conditions become overcrowdedConservation BiologyCritical questions in conservation biology is the minimum population size of a rare species required for long term viabilitySpecial case of islands- Island Biogeography: small islands far from the mainland have fewer terrestrial species than larger closer islands- MacArthur and Wilson proposed that species diversity is a balance between colonization and extinction ratesConservation Geneticsin a large population, genetic diversity tend to be preserved. A loss/gain of a few individuals has little effect on the total gene