Chapter 11 –Population Distributions:

  • Ecological suitable habitats constrain population distribution
  • Many niches in habitat for populations
  • Dispersal is essential for colonizing new areas
  • Estimations can be made for distribution properties
  • Adult body size and geographical range influences population abundance and density
  • Spatial structure:
  • Pattern of density and spacing of individuals in a population

Distribution of populations is limited to ecologically suitable habitats:

  • Fundamental niche: the range of abiotic conditions under which species can persist
  • Includes temperature, humidity, and salinity conditions
  • Influences survival, growth, and reproduction
  • Competition may lead to unoccupied areas
  • Although favourable conditions may be met, disease, predation, and competition may influence its use
  • Realized niche: the range of abiotic and biotic conditions under which a species persists
  • Determines the geographical rangeof a species or f various populations that compose a species
  • Geographical range:measure of total area covered by a population
  • Example: American chestnut tree (Castanea dentata)
  • Was a common tree in north America – could grow and reproduce under abiotic and biotic conditions
  • Fungus took over and decimated (chestnut blight)
  • Only some adults survived in specific areas
  • Created a realized niche for American chestnut

Ecological niche modelling:

  • Ecological niche modelling: the process of determining the suitable habitat conditions for a species
  • As suitability increases, so do population growth
  • This method aids in the rejuvenation of populations and species
  • Requires knowledge of biotic and abiotic limits
  • Use of historical data on population distribution
  • Models allow the use of influences of multiple variables
  • Shows impacts on species/ organisms of interest
  • Ecological envelope:
  • The range of ecological conditions that are predicted to be suitable for a species
  • Like realized niche
  • Difference is that it predicts potential areas of where a species can live
  • Aids in discovery of another habitat that is suitable for a species
  • Models help monitor the spread of invasive species
  • Can help determine the factors involved in invasive species
  • Introduction
  • Transportation
  • Establishment
  • Spread

Five characteristics of population distributions:

  1. Geographical range:described as the geographical range that a species occupies during their life time
  2. Example was the American chestnut
  3. Allows scientist to see the impact and spread of species
  4. Smaller ranges are more susceptible to natural disasters
  5. Endemic: species that live in a single, often isolated, location
  6. Cosmopolitan: species with a very large geographic range that can span several continents
  7. Abundance:total number of individuals in a population that exist within a defined area
  8. Provides measure of whether a population is thriving or on the bring of extinction
  9. Density: in a population, the number of individuals per unit area or volume
  10. Density calculated by dividing abundance by the area
  11. Dispersion: The spacing of individuals with respect to one another within the geographic range of a population
  12. Many types of dispersion in nature
  13. Clustered dispersion:
  14. A pattern of population dispersion in which individuals are aggregated in discrete groups
  15. May result via social groups
  16. Evenly spaced dispersion: a pattern of dispersion of a population in which each individual maintains a uniform distance between itself and its neighbours
  17. Example: would be how we grow crops
  18. Allows the resources to be used and spread evenly in crop growth
  19. Greater crowding means increase death rates of organisms
  20. Some will be more fit to exploit available resources while others suffer
  21. Random dispersion: a pattern of dispersion of a population in which the position of each individual is independent of the position of other individuals in the population
  22. Not common in nature
  23. Abiotic conditions, resources, and interactions with another species are not randomly distributed
  24. Dispersal: movement of individuals from one area to another
  25. Distinct from migration
  26. Migration: is the movement of individuals back and forth between habitats
  27. Dispersal involves individuals leaving their habitat of origin
  28. Allows avoidance of high competition
  29. Example from flowers dispersing seeds
  30. Reduction in competition
  31. Allows for niche environment exploitation

Distribution properties of population can be estimated:

  • Of the five characteristics, four require where the individuals are located and how many are located areas
  • Dispersal requires quantification of movement of individuals
  • Census: counting every individual in a population
  • Like the Canadian census
  • Occurs every 5 years
  • Survey: counting a subset of the population
  • Area- and volume – based surveys: surveys that define the boundaries of an area or volume and then count all the individuals in the space
  • Line-transect surveys: surveys that count the number of individuals observed as one moves along the line
  • Helps scientists see trends of population
  • Insight on which population of a species is increasing, stable, or decreasing
  • Mark-recapture survey: a method of population estimation
  • Use of capturing and marking a subset of populations from an area
  • Returning of captured specimen
  • Recollect and capture a different sample size after an amount of time has passed
  • Most common on fish, birds, mammals, and highly mobile invertebrates
  • Lifetime dispersal distance: the average distance an individual moves from where it was hatched or born to where it reproduces
  • Aids in the estimation of how rapidly a growing population can increase its geographical range
  • Example: songbirds
  • Found that average species of songbirds takes ~1000 generations to travel one continent
  • Resource availability influences population abundance in a geographical range
  • Dispersal limitations: the absence of a population from suitable habitat because of barriers to dispersal
  • Can happen naturally without the aid of human transport
  • Habitat corridor: a strip of favourable habitat located between two large patches of habitat that facilitates dispersal

Many populations live in distinct patches of habitat:

  • Natural selection favours individuals that can choose their habitat that provides most energy
  • Helps increase fitness
  • Ideal free distribution: when individuals distribute themselves among different habitats in a way that allows them to have the same per capita benefit
  • Example: stickleback
  • high abundance in both high and low quality habitats
  • found that there are other factors influencing fitness besides resources
  • predators or territory owners
  • Subpopulations:when a larger population is broken up into smaller groups that live in isolated patches

Three models range from less to more complex for subpopulations

  • Basic metapopulation model: a model that describes a scenario in which there are patches of suitable habitat embedded within a matrix of unsuitable habitat
  • Assumes each patch is of equal quality
  • Colonization and extinction events can affect proportion of total suitable habits that are occupied
  • The source – sink metapopulation model:a population model that builds upon the basic metapopulation model and accounts for the fact that not all patches of suitable habitat are of equal value
  • Source subpopulations: high quality habitats, subpopulations that serve as a source of dispersers within a metapopulation
  • Can have low quality habitats – rarely produce enough dispersers
  • Dependent on outside dispersers for subpopulation maintenance
  • Sink subpopulations: low quality habitats, subpopulations that rely on outside dispersers to maintain the subpopulation within a metapopulation
  • The landscape metapopulation model: a population model that considers both differences in the quality of the suitable patches and the quality of the surrounding matrix