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Transcript of 1 Population Dynamics. 2 Outline Dynamics of Population Growth Exponential vs. Arithmetic Growth ...
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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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