Population Dynamics

Exponential Growth and Doubling Times nEnExponential Growth: Growth at a constant rate of increase per unit of time nGnGeometric Growth: Same as exponential growth –S–Sequence of growth follows a geometric pattern of increase nAnArithmetic Growth: Growth increases at a constant amount per unit of time 6.4

nJnJ curve: Growth curve produced by a constant rate of growth –R–Represents theoretical unlimited growth –I–It represents the biotic potential

Biotic Potential nTnThe maximum reproductive rate of an organism having no limiting factors. nInIf all the individuals in the population survived and reproduced at the maximum rate. nInIt is a reference value allowing one to determine if the observed growth rate is close to the biotic potential.

Population Oscillations and Irruptive Growth nDnDieback: When death rates begin to surpass birth rates nOnOvershoot: The extent to which a population exceeds the carrying capacity of its environment nMnMalthusian (Irruptive) Growth: Pattern of population explosion followed by a population crash

Growth to a Stable Population nLnLogistic Growth: Constantly changing rate –W–When growth slows as populations approach the carrying capacity of the environment nEnEnvironmental Resistance: Factors that tend to reduce population growth rates 6.7 nSnS curve: Population growth and stabilization in response to environmental resistance

Carrying capacity n The maximum number of individuals of a certain species that an environment can support. n It reflects the limits imposed on population growth by finite space and finite resources.

Lifestyle greatly affects carrying capacity It is estimated that acres are necessary to sustain one person with an affluent lifestyle To support the 5.6 billion humans at such a lifestyle would require 3 times as much productive land In these terms, the earth can support only 1.8 billion people

Environmental resistance can include any of the following. n food runs out n waste accumulates and becomes toxic n living space runs out n over-crowding makes the population an easy target for parasites and predators n disease n predation

Calculating % Growth Rates (GR) n Population Growth for a Specific Location % GR= (birth +immigration)- (deaths+emmigration) 100

% Global Population Growth Rate % growth rate = (birth rate %-death rate percent) i.e. 6 births/100 people each year 4 deaths/100 people each year this is a rate of increase of 2%

Calculating Doubling Time DT = _____70_____ % growth rate 70 is a demographic constant

Factors that Increase or Decrease Populations n Natality, Fecundity and Fertility n Immigration and Emigration n Mortality and Survivorship n Age Structure

Natality, Fecundity, and Fertility nNnNatality: Production of new individuals by birth, hatching, germination, or cloning –M–Main source of addition to most biological populations nFnFecundity: Physical ability to reproduce “Potential” nFnFertility: Measure of actual number of offspring produced “Actual or Realized”

Migration nInImmigration: movement of organisms into a new ecosystem nEnEmigration: movement of organisms out of an ecosystem **Migration is not a factor when determining Global Population Growth Rates

Mortality and Survivorship nMnMortality: Death rate –D–Determined by dividing number of organisms that die in a certain time period by the number alive at the beginning of the period 6.9 nSnSurvivorship: Percentage of a cohort that survives to a certain age

Life Span vs Life Expectancy nLnLife Span: Longest period of life reached by a given type of organism 6.10 nLnLife Expectancy: The probable # of years of survival for an individual of a given age

Age Structure nPnPopulation Momentum: Large number of prereproductive individuals –R–Rapid increase in natality once youngsters reach reproductive age 6.11

Factors That Regulate Population Growth n Dn Density-Dependent: Effects are stronger or a higher proportion of the population is affected as population density increases nDnDensity-Independent: The effect is the same or a constant proportion of the population is affected regardless of population density

More….. nInIntrinsic: Factors operating within individual organisms or between organisms in the same species nEnExtrinsic: Imposed from outside the population nBnBiotic: Caused by living organisms nAnAbiotic: Caused by nonliving components of the environment

Characteristics of contrasting reproductive strategies Extrinsically Controlled GrowthIntrinsically Controlled Growth Short LifeLong Life Rapid growthSlower growth Early maturityLate maturity Little parental care or protectionHigh parental care and protection Little investment in individual offspringHigh investment in individual offspring Adapted to unstable environmentAdapted to stable environment Pioneers, colonizersLater Stages of succession Niche generalistsNiche specialist PreyPredators Regulated mainly by extrinsic factorsRegulated mainly by intrinsic factors Low trophic levelsHigh trophic levels

Density-Independent Factors nFnFactors that affect natality of mortality independently of populations density abiotic

Density-Dependent Factors nFnFactors that reduce population size by decreasing natality or increasing mortality –T–Tend to be biotic nInInterspecific Interactions: Two species compete for the same environmental resources in an ecosystem 6.12 –M–May be beneficial or neutral, such as mutualism

nInIntraspecific Interactions –I–Individuals within a population compete for resources –T–Territoriality is an example nSnStress and Crowding –S–Stress Shock: A loose set of physical, psychological, and/or behavioral changes thought to result from the stress of excess competition and extreme closeness to other members of the same species