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Population Dynamics
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Outline
•Dynamics of Population Growth
•Factors That Increase or DecreasePopulations
•Factors That Regulate Population Growth
•Conservation Biology
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DYNAMICS OF POPULATION GROWTH
•Exponential Growth - Growth at a constantrate of increase per unit time. (Geometric)
dN/dt = rN
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Exponential Growth and Doubling Times
•Number of individuals added to a populationat the beginning of exponential growth isrelatively small. But numbers increasequickly as the population, and thus the givenpercentage of that population, grows.
J curve
•Doubling Time of a population:
70/annual percentage growth rate.
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Biotic Potential and Carrying Capacity
•Biotic Potential - Maximum reproductive rateof an organism.
•Carrying Capacity - Maximum number ofindividuals of any species that can beindefinitely supported in a given area.
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Boom and Bust Cycles
•Overshoot - Measure of extent to whichpopulation exceeds carrying capacity of itsenvironment.
•Dieback - Negative growth curve.
Severity of dieback generally related to theextent of overshoot.
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Growth to a Stable Population
•Logistic Growth - Growth rates regulated byinternal and external factors until coming intoequilibrium with environmental resources.
dN/dt = r N (1 - N/K)
Growth rate slows as populationapproaches carrying capacity.
S curve
•Environmental Resistance - Anyenvironmental factor that reduces populationgrowth.
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r-Adapted Species
•Short life
•Rapid growth
•Early maturity
•Many small offspring
•Little parental care
•Little investment inindividual offspring.
•Adapted to unstableenvironment.
•Pioneers, colonizers
•Niche generalists
•Prey
•Regulated mainly byextrinsic factors.
•Low trophic level
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K-Adapted Species
•Long life
•Slower growth
•Late maturity
•Fewer largeoffspring
•High parental careand protection.
•High investment inindividual offspring.
•Adapted to stableenvironment.
•Later stages ofsuccession.
•Niche specialists
•Predators
•Regulated mainly byintrinsic factors.
•High trophic level
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FACTORS THAT INCREASE ORDECREASE POPULATIONS
•Natality - Production of new individuals .
Fecundity - Physical ability to reproduce.
Fertility - Measure of actual number ofoffspring produced.
•Immigration - Organisms introduced into newecosystems.
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Mortality, Survivorship, and Emigration
•Mortality - Death Rate.
Survivorship - Percentage of cohortsurviving to a certain age.
Life expectancy - Probable number of yearsof survival for an individual of a given age.
-Increases as humans age.
Life Span - Longest period of life reached bya given type of organism.
•Emigration - Movement of individuals out of apopulation.
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Survivorship Curves
•Four general patterns:
Full physiological life span.
Probability of death unrelated to age.
Mortality peaks both early and late in life.
Mortality peaks early in life.
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Survivorship Curves
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FACTORS THAT REGULATE POPULATION GROWTH
•Intrinsic factors - Operate within or betweenindividual organisms in the same species.
•Extrinsic factors - Imposed from outside thepopulation.
•Biotic factors - Caused by living organisms.
•Abiotic factors - Caused by non-livingenvironmental components.
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Density Independent Factors
•Constant proportion of the population isaffected regardless of population density.
•Tend to be abiotic components.
•Do not directly regulate population size.
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Density Dependent Factors
•Higher proportion of population is affected aspopulation density increases.
•Tend to reduce population size bydecreasing natality or increasing mortality.
Interspecific Interactions
-Predator-Prey oscillations
Intraspecific Interactions
-Territoriality
Stress and Crowding
-Stress-related diseases
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CONSERVATION BIOLOGY
•Island biogeography - Small islands far froma mainland have fewer terrestrial speciesthan larger, closer islands.
MacArthur and Wilson proposed thatspecies diversity is a balance betweencolonization and extinction rates.
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Conservation Genetics
•Genetic Drift
Random reduction in gene frequency.
•Founder Effect
Few individuals start a new population.
•Demographic Bottleneck
Few individuals survive catastrophe.
-Inbreeding
Mating between related individuals.
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Genetic Drift
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Population Viability Analysis
•Minimum Viable Population is the minimumpopulation size required for long-termviability of a species.
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Metapopulations
•A collection of populations that have regularor intermittent gene flow betweengeographically separate units.
Bay Checkerspot Butterfly
-Source - Sink Model
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Summary
•Dynamics of Population Growth
•Factors That Increase or DecreasePopulations
•Factors That Regulate Population Growth
•Conservation Biology
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