1 Population Dynamics

2 Outline Dynamics of Population Growth Factors That Increase or Decrease Populations Factors That Regulate Population Growth Conservation Biology

3 DYNAMICS OF POPULATION GROWTH Exponential Growth - Growth at a constant rate of increase per unit time. (Geometric) dN/dt = rN

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 Doubling Time of a population:  70/annual percentage growth rate.

5 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.

6 Boom and Bust Cycles 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 Growth to a Stable Population Logistic Growth - Growth rates regulated by internal and external factors until coming into equilibrium with environmental resources.  dN/dt = r N (1 - N/K)  Growth rate slows as population approaches carrying capacity.  S curve Environmental Resistance - Any environmental factor that reduces population growth.

8 r-Adapted Species 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

9 K-Adapted Species 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

10 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.

11 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.

12 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.

13 Survivorship Curves

14 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.

15 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.

16 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

17 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.

18 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.

19 Genetic Drift

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

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

22 Summary Dynamics of Population Growth Factors That Increase or Decrease Populations Factors That Regulate Population Growth Conservation Biology

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