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Population Dynamics

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Outline

• Dynamics of Population Growth Exponential vs. Arithmetic Growth Malthusian vs. Logistic Growth

• Population Increase• Population Decrease• Survivorship• Regulating Population Growth

Density Dependence vs. Independence• Conservation Biology

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DYNAMICS OF POPULATION GROWTH

• Exponential Growth - Growth at a constant rate of increase per unit time. (Geometric)

• Arithmetic Growth - Growth at a constant amount per unit time.

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Exponential Growth and Doubling Times

• Number of individuals added to a population at the beginning of exponential growth is relatively small. But numbers increase quickly as the population, and thus the given percentage 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 rate of an organism.

• Carrying Capacity - Maximum number of individuals of any species that can be indefinitely supported in a given area.

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Population Oscillations

• Overshoot - Measure of extent to which population exceeds carrying capacity of its environment.

• Dieback - Negative growth curve. Severity of dieback generally related to the

extent of overshoot.

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Irruptive Growth

• Malthusian Growth (Irruptive) - Population explosions followed by population crashes. Malthus concluded human populations

tend to grow until they exhaust their resources and then crash.

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Growth to a Stable Population

• Logistic Growth - Growth rates regulated by internal and external factors until coming into equilibrium with environmental resources. Growth rate slows as population

approaches carrying capacity. S curve

• Environmental Resistance - Any environmental factor that reduces population growth.

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Malthusian Strategies

• Short life• Rapid growth• Early maturity• Many small offspring• Little parental care• Little investment in

individual offspring.

• Adapted to unstable environment.

• Pioneers, colonizers• Niche generalists• Prey• Regulated mainly by

extrinsic factors.• Low trophic level

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Logistic Strategies

• Long life• Slower growth• Late maturity• Fewer large

offspring• High parental care

and protection.• High investment in

individual offspring.

• Adapted to stable environment.

• Later stages of succession.

• Niche specialists• Predators• Regulated mainly by

intrinsic factors.• High trophic level

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FACTORS THAT INCREASE OR DECREASE POPULATIONS

• Natality - Production of new individuals . Fecundity - Physical ability to reproduce. Fertility - Measure of actual number of

offspring produced.• Immigration - Organisms introduced into new

ecosystems.

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Mortality, Survivorship, and Emigration

• Mortality - Death Rate. Survivorship - Percentage of cohort

surviving to a certain age. Life expectancy - Probable number of years

of survival for an individual of a given age.- Increases as humans age.

Life Span - Longest period of life reached by a given type of organism.

• Emigration - Movement of individuals out of a population.

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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 between individual organisms in the same species.

• Extrinsic factors - Imposed from outside the population.

• Biotic factors - Caused by living organisms.• Abiotic factors - Caused by non-living

environmental components.

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Density Independent Factors

• Constant proportion of the population is affected 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 as population density increases.

• Tend to reduce population size by decreasing 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 from a mainland have fewer terrestrial species than larger, closer islands. MacArthur and Wilson proposed that

species diversity is a balance between colonization 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 minimum population size required for long-term viability of a species.

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Metapopulations

• A collection of populations that have regular or intermittent gene flow between geographically separate units. Bay Checkerspot Butterfly

- Source - Sink Model

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Summary

• Dynamics of Population Growth Exponential vs. Arithmetic Growth Malthusian vs. Logistic Growth

• Population Increase• Population Decrease• Survivorship• Regulating Population Growth

Density Dependence vs. Independence• Conservation Biology

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