Population Biology

• Population biology


  The study of the distribution and abundance of living organisms and how those properties are influenced by interactions between the organisms and their environment
• Levels of biological organization


  • Biosphere
  • Landscapes
  • Ecosystems
  • Communities
  • Populations
  • Individual organisms
  • Organ systems
  • Tissues
  • Cells
  • Subcellular organelles
  • Molecules
• Distribution and abundance


  The study of where organisms live and how many there are
• Overbreeding of rabbits in Australia led to heteronomous
• Rabbit population grew out of control, took over the ecosystem (still a problem 150 years later)
• Lotus' behaviour and physiology has changed to best utilise their mass, possibly a stress-based response
• Large colonies of king penguins indicate a breeding phase or cycle
• Spatial distribution diversity


  • Uniform distribution
  • Aggregated/clumped
  • Random
  • Highly aggregate
• Heat map convention for density


  High density -> darker colour; lower density -> lighter cooler
• BBS


  Biological limit line
• Approaches in population biology

  • Descriptive: Foundation knowledge and data collection
  • Proximate causes: Dynamic response to immediate factors
  • Ultimate causes: Historical reasons why natural selection favours key adaptations
• Population


  A group of individuals of the same species that live within a particular area and interact with one another
• Abundance


  Can be reported as population size (number of individuals) or density (number of individuals per unit area)
• On a 20-hectare island there are 2500 lizards. Population size: 2500, Population density: 125/hectare
• Patchy populations


  Populations may exist in patches that are spatially isolated but linked by dispersal, resulting from physical features of the environment and human activities that subdivide populations
• A grove of aspens may all be from the same individual, and other plants/fungi, corals, bryozoans, sea anemones, some insects, fish, frogs, and lizards can also form clones
• Armillaria ostayae is a huge organism found in cool northern hemisphere biomes, 2400 years old spanning Maher National Forest
• Methods for measuring abundance


  • Total counts
  • Quadrants count
  • Capture-mark-recapture estimate
  • Relative indices (trapping, catch per unit effort, spraint and scat, vocalisation frequency, percentage cover, pelt records, roadside counts or lamping)
• No population can increase in size forever, species have a capacity for rapid population growth, and we try to understand the factors that limit or promote population growth
• Survivorship curve


  Shows that there is very little reproduction when survivorship is high
• Life tables


  Show how survival and reproductive rates vary with age, size, or life cycle stage
• Sx


  Age-specific survival rate, the chance that an individual of age x will survive to age x +1
• Lx


  Survivorship, the proportion of individuals that survive from birth (age 0) to age x
• Fx


  Fecundity, the average number of offspring produced by a female while she is of age x
• Demographics


  The measurement and understanding of the average person
• Demographic approaches


  • Cohort based
  • Static based
• Lx = Nx/No (survivorship from birth)
• Eo


  Life expectancy at birth
• Gross reproductive rate (GRR)


  The mass amount of reproduction possible (Σf_x)
• Net reproductive rate (NRR)


  Survivorship and reproductive rate together (Σ l_x m)
• Ro


  Replacement rate, greater than 1 population increase, less than 1 population decrease, 1 = population stable
• Semelparous


  Single breeding event/timed event (born -> develops -> reproduces -> dies)
• Iteroparous


  Continuous event over lots of time (much longer period of development and reproduction)
• T


  How much change occurs in a small period of time
• R ≈lr R_O/T=log⁡〖2.9/1.68 =1.06/1.68=0.7〗
• Age structure


  The proportion of the population in each age class, which influences whether a population will increase or decrease in size
• Populations can change in size as a result of four processes: birth, death, immigration, emigration
• Geometric method


  Nt+1 = R0Nt
• Exponential method


  Nt = N0ert, where r is the per capita growth rate
• Exponential growth


  Can occur when a species reaches a new geographic area with favourable conditions, leading to rapid population growth until density-dependent factors regulate its numbers