UNCG 301 Ecology UNIT 2

• A population is a group of individuals of the same species that inhabit a given area
• Populations have structure, including density, spacing and age distribution
• Populations are dynamic, changing over time
• Individuals within populations are descended from those alive at an earlier time
• Individuals within populations share a common history of adaptation to local conditions
• Populations have collective attributes such as abundance, distribution, dispersion, age structure, and sex ratio
• Demography is the quantitative study of population attributes/traits
• The distribution of a population is the area over which it occurs
• The geographic range of a species encompasses all the individuals of a species
• Ubiquitous species have a geographically widespread distribution
• Endemic species have a geographically restricted distribution
• The distribution of an organism can be limited by geographic barriers such as bodies of water, mountains, and unsuitable habitats
• Individuals are not distributed equally across a geographic range and are found in suitable habitat patches surrounded by unsuitable habitat
• Abundance reflects population density and distribution, and can be expressed as the total number of individuals in a population or as density (individuals per unit area or volume)
• Abundance can be influenced by factors like random distribution, uniform distribution, or clumped distribution
• Ecological density is the number of individuals per unit of available living space
• Determining density requires sampling methods like quadrats/sampling units and mark-recapture techniques
• Lincoln-Peterson index method for relative population size:

  • Assumes random sampling
  • Assumes equal chance of capture for each individual
  • Assumes marked individuals are randomly distributed
  • Assumes enough time for mixing into the population
  • Assumes ratio of marked and unmarked individuals remains constant
  • Assumes marking method does not affect survival
• Measures of population structure:

  • Abundance does not provide individual characteristics
  • Non-overlapping generations lack age structure
  • Overlapping generations have age structure
  • Populations can have pre-reproductive, reproductive, and post-reproductive age classes
  • Age pyramid shows age structure at a specific time
  • Pyramid shape indicates future population growth
• Sex ratios in populations:

  • Sex ratio close to 1:1 in sexually reproducing organisms
  • Mammalian populations have a slight male bias at birth
  • Sex ratio shifts towards females in older age classes
  • Birds tend to have more males than females
  • Nesting females may be more susceptible to predation
• Individual movement within populations:

  • Dispersal influences population density
  • Dispersal includes emigration and immigration
  • Metapopulation dynamics involve movement between subpopulations
  • Passive dispersal methods include wind, water, gravity, and animals
  • Active dispersal varies by species and age class
  • Migration is round-trip movement of organisms
• Population distribution and density changes:

  • Dispersal shifts spatial distributions and affects subpopulation density
  • Dispersal can expand the geographic range of a population
  • Environmental conditions and climate change can lead to temporal shifts in population distribution
  • Human activities can aid in the dispersal of species, impacting geographic ranges
• Processes that increase population size:

  • Births
  • Immigration
• Processes that decrease population size:

  • Deaths
  • Emigration
• Difference between open and closed populations:

  • An open population has immigration and emigration
  • A closed population does not have or has a very low level of immigration and emigration that doesn’t influence population growth
• Individuals are added to a population through births and immigration
• Individuals leave the population through deaths and emigration
• Changes in population size over time are calculated using the formula:

  N(t+1) = N(t) + B(t) - D(t) + I(t) - E(t)
• In a closed population, there is no immigration or emigration affecting population growth
• Hydra population example:

  • Monitoring a population of organisms with a simple life cycle
  • Most reproduction is asexual by budding
  • All reproduce asexually and have one offspring at a time
• Budding in the Hydra population:

  • Produces new Hydra through births
  • Some Hydra die daily
  • Processes of budding and deaths are continuous and not synchronized
  • 40 new Hydra are produced daily
  • 10 Hydra die daily
• Per capita birth rate (b) and death rate (d) are constant and can be used to predict population growth over time regardless of population size
• Equation for predicting population growth:

  N(t+1) = N(t) + bN(t) - dN(t)
• Geometric population growth pattern is observed in the Hydra population
• Quiz Question #1: Is the Hydra population open or closed?

  • Closed
• Quiz Question #2: Per capita birthrate calculation:

  • Birth Rate = 0.05
• Quiz Question #3: Per capita death rate calculation:

  • Death Rate = 0.2
• Quiz Question #4: Population size on day 1:

  • 48
• Population is shrinking
• Intraspecific population regulation involves density dependence