5. Population Eco

• Population - group of individuals belonging to the same species living together in a particular place at a particular time
• Population - studied in Ecology because the individuals making them up use the same resources in a certain area, are affected by the same conditions in the area and interact with other organisms in the same way
• Population studies - hold the key to saving endangered species and controlling pest populations and disease epidemics
• Population Ecology - study of populations in relation to the environment
• Populations have emergent properties that are not present in the lower level of organization, individuals.
• Emergent properties of populations

  1. Population size
  2. Population density
  3. Natality rate (birth rate)
  4. Mortality rate
  5. Age distribution
  6. Population growth rate
  7. Population distribution
• Population distribution - The values of these properties change from time to time (population dynamics, demography).
• Variables affecting population size

  1. Number of births (B)
  2. Number of deaths (D)
  3. Number of immigrants (I)
  4. Number of emigrants (E)
  5. Change in population size (ΔN/ΔT)
• Changes in population size

  (ΔN/ΔT) = (B + I) - (D +E)
• Population size increases when (B + l) > (D + E).
• Population density - number of individuals per unit of geographic area
• Population density is higher to areas with plentiful resources rather than areas with scarcity of resources
• Higher population density will deplete resources and leads to competition
• TRUE OR FALSE: Population density is a more useful quantity than population size because it relates the number of individuals and the wastes they produce with the amount of resources available in a unit of area (TRUE)
• Natality - ability of a population to increase in size through reproduction whether by giving birth (sexual reproduction), budding or fission (asexual reproduction)
• Maximum natality - greatest number of new individuals produced under ideal environmental conditions
• Realized natality - number of new individuals produced under actual environmental conditions.
• Mortality - number of deaths in a population
• TRUE OR FALSE: Mortality rates increase with age (TRUE)
• Minimum mortality - theoretical minimum laws under ideal (non-limiting) conditions
• Realized mortality - actual death rate observed under existing or actual conditions
• Realized mortality - occurs when environmental conditions are ideal, but often, environmental conditions cause organisms to die earlier than their physiological longevity would allow
• Birth rate - number of new individuals/births that occur per one thousand people, per year
• Survivorship - how many individuals of a species born together (a cohort) are still alive at different age intervals.
• Three Kinds of Survivorship

  1. Type I
  2. Type II
  3. Type III
• Type I Survivorship

  • Humans, large mammals
  • Convex shape; late loss
  • This is shown by many large mammals with few offspring that are quite large, including humans 
  • survivorship is high (and mortality rate low) when the individuals of the population are still young
  • Mortality rates increase with age (growing older)
• Type II Survivorship

  • Birds, mouse
  • Diagonal line; constant loss
  • Mortality does not depends on its age; chance of dying independent of age
  • Constant mortality rate throughout its entire life
• Type III Survivorship

  • Observed in oysters, clam, shellfish
  • Clams vulnerable to predators in larval stage
  • Surviving through attaching to substrate
  • many individuals of the population die at the free-swimming larval stage due to predation, but once the larvae have attached to a substratum and secrete the shell, more individuals survive (mortality rate decreases)
  • Concave in shape; early loss
• Type III Survivorship

  Most of these organisms die right away

  • High death rate following birth, they don't have parental care to their offspring
  • This type of curve is shown by species that do not provide parental care to their offspring.
• Kinds of Age Pyramids

  1. Expanding
  2. Stable
  3. Collapsing
• Expanding Age Pyramid

  • much greater number of young individuals in the population
  • rapid growth of population in the future
  • Examples: India, Kenya, Afghanistan, and Philippines
• Stable Age Pyramid

  • also a greater number of young individuals but the difference is not that matched
  • slow growth
  • Example: United States, Canada, Australia
• Collapsing Age Pyramid

  • population size declining since there is a greater number of older people compared to younger population
  • young not enough to replace younger population
  • Examples: Japan, Germany, Italy, and many other European countries
• Age distribution

  1. Pre-reproductive

  • From birth up to the pre-pubescent stage
  • 0- 14 years old

  1. Reproductive

  • 15 - 44 years

  1. Post-reproductive

  • 45 to end of life
• No. of births and deaths in a population

  • Can be expressed as the average number of births and deaths per individual (per capita) during the time period.
• Per capita birth rate (b)

  • The number of offspring produced per unit time by an average member of the population
  • By convention it is the number of births per 1000 individuals
• • Birth rate
  • If there are 34 births per year in a population of 1000 individuals, the annual per capita birth rate is 34/1000 or 0.034. 
  • Death rate
  • If 16 deaths in 1000 persons, then per capita death rate is 0.016.
• • Population growth rate in a year
  • b-d = r
• r

  • Also the per capita rate of increase
  • The difference between per capita birth and death rate, with emigration and immigration ignored.
  • also called the population growth rate, expressed on a per capita basis.
• • If b>d, r is >0 or a positive value, population is increasing
  • If r<0, population is decreasing
  • r = 0, same population size.
  • r = 0.034 - 0.016 = 0.018 or 1.8% per year