S_L1: Distribution and Abundance

• Organisms with uniform spatial distribution tend to have limited dispersal abilities and are often habitat specialists.
• Natality


  Includes the production of new individuals
• Interpretation


  Relating model components (parameters, variables) and model behavior to components, characteristics, and behavior of real systems
• Potential vs realized mortality


  How to measure mortality
• Common assumptions in population studies: Immigration = emigration
• How may it happen that the wrong model can give a correct answer?
• Fertility


  Based on number of offspring
• Modular vs. unitary organisms: Modular (Clonal)
• Factors that determine density: Natality - birth rate
• Abstraction


  Generalization: taking the most important components of real systems and ignoring less important components
• Longevity


  Age of death of individuals in population
• Realized vs. potential fertility


  Usually reported as organisms produced per female per unit time
• Assume closed system e.g. islands, where dispersal is of little importance
• Models

  1. The importance of models

  2. Models are a tool

  3. Model and reality are linked together by two procedures: abstraction and interpretation
• Modelling strategy

  • Select optimal level of complexity
  • Avoid the temptation to incorporate all available information into the model
  • Follow specific objectives, don't try to make a universal model
  • If possible, incorporate existing models
• Self-Regulation of Logistic Growth Model

  1. Sigmoid curve

  2. Growth rate gradual initially = lag, then rapid = exponential, then slows = stationary

  3. Population or system reached max size or carrying capacity
• Death rate is the converse of survival
• Dispersal can be measured with the advent of radio-telemetry, primarily limited to larger organisms
• Richard Feynman: '“People who wish to analyze nature without using mathematics must settle for a reduced understanding.”'
• Mortality: Catch Curves

  Survival rate between years 2 and 3 = Relative abundance of fish at age III / Relative abundance of fish at age II = 0.50
• Fecundity


  Potential reproductive capacity
• Models are always "wrong": '...but many of them are useful'
• Composition & richness are studied using 5 x 5m quadrats to measure abundance & density in forest/grassland
• Distribution is a function of scale, often range and abundance are positively correlated. Population ecology is often concerned about density affected by natality, mortality, immigration, and emigration. Measuring density can be relative or absolute
• Measures of relative density (not absolute) include traps, vocalization frequency, catch per unit effort, percent cover, roadside counts, etc.
• Class exercise: How to calculate the number of students in a BIOL305 class?
• How can density be determined?

  1. Measuring absolute density through census, counting trees, etc.

  2. Sampling and statistics by sample areas and extrapolating
• Other sampling methods

  Transects, Time counts, Mark and recapture
• Example of mark and recapture: Marked animals in 1st sample, release and sample again in 2nd sample, then calculate the total population size
• Individual units (Unitary) include organisms like you, deer, mice, etc.
• Sampling quadrats


  Sample a proportion to estimate the whole area
• Some organisms come in simple units of individuals (Modular), example: grass, corals
• Factors that determine density: Immigration and emigration
• Divide study area into quadrats

  Count density in subset of squares, then average the survey to estimate the whole area