Sci 11

• Life tables


  Summary of birth and death rates for organisms at different stages of their lives
• Survivorship curves


  Graphs that show what fraction of a population survives from one age to the next
• Age-sex pyramid


  A "snapshot" of a population in time showing how its members are distributed among age and sex categories
• Governments around the world keep records of human birth and death rates—not just for the overall population of a country but also for specific groups within it, broken down by age and sex
• Ecologists often collect similar information for the species they study, but they don't do it to maximize profits! They do it to gain knowledge and, often, to help protect species
• By combining birth and death rates with a "snapshot" of the current population—how many old and young organisms there are and whether they are male or female—ecologists can predict how a population is likely to grow or shrink in the future
• Dall mountain sheep


  A wild sheep of northwestern North America
• For practical reasons, most ecologists still use shortcuts like Murie's to estimate survival and death rates from data collected in a short period rather than following large groups of organisms over long periods
• The life table shows when the sheep have the greatest risk of death, with one high-risk period being between 0.5 and 1 years and another being late in life, starting around age eight
• Survivorship curve


  A graph that shows what fraction of a starting group is still alive at each successive age
• Types of survivorship curves

  • Type I
  • Type II
  • Type III
• Age-sex structure


  Information about the current distribution of a population by age and sex
• Large fractions of young and reproductive individuals mean a population is likely to grow, while large fractions of individuals past reproductive age mean a population is likely to shrink
• Japan has a shrinking population, with a population pyramid that pinches inward towards its base, reflecting that young people are a small fraction of the population
• The estimation of survival schedules in natural populations employs several sampling techniques.
• Life history patterns.
• Population dynamics


  Looks at how the population of a country, region, or the world changes, taking into account factors that increase and decrease population to create a total growth rate
• Factors that contribute to total growth rate

  • Fertility
  • Migration
  • Mortality
• Fertility


  The natural ability of human beings to have babies, which adds to the population
• Migration


  The number of people moving into and out of countries, which doesn't change the total number of people living on the planet but does change the number in a specific country or region
• Mortality


  The fact that everyone eventually dies, which decreases the population
• Birth rate


  The number of births per 1,000 people
• Total fertility rate


  The number of kids a woman is predicted to give birth to in her childbearing years
• A total fertility rate of exactly 2 neither adds nor subtracts from the population, as the woman is giving birth to the number of people that created the children
• A fertility rate of less than 2 will decrease the population
• Immigration


  The movement of people into a country, which increases the population
• Emigration


  The movement of people out of a country, which decreases the population
• Mortality rate


  The number of deaths per 1,000 people
• Population pyramid


  • Graphs the age and sex distribution of a population, with males and females on either side and increasing age along the vertical axis
• Stationary or constrictive pyramid


  Indicates low birth rates and low death rates throughout the population, with more elderly people living a long time and dying of old age
• Expansive pyramid


  Indicates high birth rates and high death rates, with more young people dying from disease
• Age-specific mortality rates


  Mortality rates for specific age ranges, allowing for better comparisons between countries
• Life table or mortality table


  Tells the probability that someone will die given their age, which can vary from country to country
• Emigration rate


  The number of people emigrating per 1,000 people in the country
• Net migration


  The difference between the number of people entering the country and the number of people leaving the country
• Internal migration, where people move within their own country, doesn't change the total population but can affect the economics or cultures of a country
• The growth rate of a country is calculated as the initial population, plus births, minus deaths, plus immigration, minus emigration
• Some countries have a negative growth rate as more people die and leave than are born and move in
• • Density-dependent limiting factors cause a population's per capitagrowth rate to change—typically, to drop—with increasing population density. One example is competition for limited food among members of a population.
• • Density-independent factors affect per capita growth rate independent of population density. Examples include natural disasters like forest fires.