Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Population Dynamics Chapter 6

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Outline: Dynamics of Population Growth  Exponential vs. Arithmetic Growth  Malthusian vs. Logistic Growth Population Increase Population Decrease Survivorship Age Structure Regulating Population Growth  Density Dependence vs. Independence

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Exponential Growth 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-shaped curve

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Population Measures Doubling Time of a population:  70/annual percentage growth rate. Biotic Potential - Maximum reproductive rate of an organism.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed.

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.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed.

Malthusian Growth Malthusian Growth (Irruptive Growth) - Population explosions followed by population crashes.  Malthus concluded human populations tend to grow until they exhaust their resources and then crash.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Logistic Growth Logistic Growth - Growth rates regulated by internal and external factors until come into equilibrium with environmental resources.  Growth rate slows as population approaches carrying capacity.  S-Shaped curve Environmental Resistance - Any environmental factor that reduces population growth.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Chaotic and Catastrophic Dynamics Chaotic Systems - Exhibit variability in a complex pattern not observable under normal human scales.  Edward Lorenz - Butterfly effect. Catastrophic System - May jump from one steady state to another without any intermediate stages.  Balancing chair on two legs.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. FACTORS INCREASING OR DECREASING 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.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Population Decrease 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.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Survivorship Curves

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Age Structure Growing or declining populations usually have very different proportions of individuals in various age classes.  Rapidly expanding populations - Have large number of pre-reproductive individuals and thus have population momentum. - Diagram shows large base.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Age Structure  Stationary Populations - Balanced when natality and mortality are equivalent. - Diagram shows no bulges.  Diminishing Populations - Natality has fallen below replacement level. - Diagram shows bulge in upper age classes.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed.

REGULATING 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.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Density Dependent Factors Higher proportion of population is affected as population density increases. Tend to reduce population size by decreasing natality or increasing mortality as population size increases.  Interspecific Interactions - Predator Prey oscillations  Intraspecific Interactions - Territoriality - Stress-related diseases

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Summary: Dynamics of Population Growth  Exponential vs. Arithmetic Growth  Malthusian vs. Logistic Growth Population Increase Population Decrease Survivorship Age Structure Regulating Population Growth  Density Dependence vs. Independence

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed.