Population

• Population


  A group of the same species that lives in one area
• 5 Characteristics of Population


  • Geographic Distribution
  • Density
  • Dispersion
  • Growth Rate
  • Age Structure
• Geographic Distribution


  The range of the population, describes the area that is inhabited by the population
• Population Density


  The number of individuals per unit area
• If scientists sampling a population of deer counted 200 individuals in an area of 10 square kilometers, the density of this deer population is 20 deer per square kilometer
• Types of Dispersion


  • Clumped Dispersion
  • Even Dispersion
  • Random Dispersion
• Clumped Dispersion


  Individuals are clustered together, occurs when resources are clumped or species have certain social behavior
• Even Dispersion


  Individuals are separated by a fairly even distance, occurs as a result of social interaction and competition for limited resources
• Random Dispersion


  Location of one individual is independent of the location of the other individuals, examples include seed dispersal
• Growth Rate


  The amount by which a population's size changes in a given time, a measure of the speed of reproduction
• Factors affecting population size


  • The number of births
  • The number of deaths
  • Migration
• Immigration


  The movement of individuals into an area
• Emigration


  The movement of individuals out of an area
• If more individuals are being born than die in a given period of time

  The population size will increase
• If birthrate is equal to death rate


  The population size will remain stable
• If the death rate is greater than the birthrate

  The population will decrease
• Carrying Capacity (K)


  The maximum number of organisms a given area can support
• Factors Limiting Population


  • Competition
  • Predation
  • Parasitism and disease
  • Drought and other climate extremes
  • Human disturbances
• Types of Limiting Factors


  • Density-Dependent Factors
  • Density-Independent Factors
• 1. Strategists


  Population usually NOT near carrying capacity, J-curve growth (high growth rate), highly affected by abiotic factors, small body size and short life span, have many offspring in a short time
• 1. Strategists


  Population lives near its carrying capacity, S-Curve Growth, Logistic Growth, highly affected by biotic factors like competition, usually large body size, have few offspring, but live a long time
• The growth of a population depends on how many people make up the given population, and the future growth of a population is predicted using age-structure diagrams
• An age-structure diagram shows the population of a country broken down by gender and age group, with each bar representing individuals within a 5-year range
• In an age-structure diagram with many more children than older groups, and fewer individuals in each higher age group


  It can reasonably be predicted that the population will experience rapid growth in the future as the large number of children reach adulthood
• For most of human existence, the human population grew very slowly due to limiting factors like lack of food and rampant diseases
• About 500 years ago, the human population began to grow at a staggering rate due to factors like the beginning of agriculture and industry, availability of food, improved sanitation and living conditions, and a drop in death rate while birth rate increased
• As a result of the staggering human population growth


  The human population is experiencing exponential growth
• The human population cannot continue to grow in this exponential manner as the resources on Earth are limited
• Demography is the scientific study of human populations, and birthrates, death rates, and the age structure of a population help predict why some countries have a higher growth rate than other countries
• Age structure describes how many individuals are present at different ages (or stages) within a population.
• Birthrate refers to the number of live births per year per thousand people in a given country or region.
• Natural increase is the difference between the birthrate and the death rate in a given area over time.
• Death rate refers to the number of deaths per year per thousand people in a given country or region.
• Natural increase is the difference between the birthrate and death rate in a given area.
• Migration is when people move from one place to another permanently or temporarily.
• Migration is the movement of people from one place to another.
• Immigration is the arrival of new residents, while emigration is the departure of existing residents.
• Population growth occurs when there is a net gain in population due to natural increase and/or net migration.
• What is population ecology?