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Population Dynamics

Population Dynamics. 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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Population Dynamics

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  1. Population Dynamics

  2. 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

  3. DYNAMICS OF POPULATION GROWTH • Biotic Potential- if unrestrained, it is the reproduction that could occur in the absence of competition, predation, disease, accident, or the scarcity of resources. - Maximum reproductive rate of an organism. • Exponential Growth - Growth at a constant rate of increase per unit time. (Geometric) • Arithmetic Growth - Growth at a constant amount per unit time.

  4. 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 is created Equation: dN = rN dt N= change in number t-= per change in time r= rate of increase

  5. Biotic Potential and Carrying Capacity • Carrying Capacity - Maximum number of individuals of any species that can be indefinitely supported in a given area. • Population Crash- a rapid dieback due to shortages of food or other resources • Lead to boom and bust cycles which could eventually lower the carrying capacity of the ecosystem

  6. 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.

  7. 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.

  8. 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 shaped graph • Equation: dN = rN(1- N/K) dt • Environmental Resistance - Any environmental factor that reduces population growth. • Density Dependent- growth rate depends on population density ie crowding, stress, disease • Density Independent Factors- abiotic factors such as drought, fire, or habitat destruction Shows population size as a proportion of carrying capacity

  9. 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 Malthusian Strategies(r- Selective Species) • Employ high reproductive rate to overcome mortality • They could overshoot the carrying capacity  population crash • Some young do survive

  10. 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 Logistic StrategiesK- Selected Species Growth slows as the carrying capacity is approached Reproduce conservatively

  11. FACTORS THAT INCREASE OR DECREASE POPULATIONS“BIDE” • Natality - Production of new individuals . • Fecundity - Physical ability to reproduce. • Fertility - Measure of actual number of offspring produced. • Immigration - Organisms introduced into new ecosystems.

  12. 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.

  13. 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.

  14. Survivorship Curves

  15. 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. (Density dependent and independent factors can affect these)

  16. 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. • Weather, climate changes, volcanic eruptions, storms, floods, landslides, plus the time of year in which they occur • Can be beneficial also- periodic fires or rainfalls change the environment to allow some species to survive- they need the disturbance

  17. 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 • Mutualism and Commensalism- good outcomes • Intraspecific Interactions • Territoriality • Stress and Crowding • Stress-related diseases

  18. 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.

  19. 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. • Good and bad results can occur

  20. Genetic Drift

  21. Population Viability Analysis • Minimum Viable Population is the minimum population size required for long-term viability of a species.

  22. Metapopulations • A collection of populations that have regular or intermittent gene flow between geographically separate units. • Bay Checkerspot Butterfly • Source - Sink Model

  23. 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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