Population%20Concepts

1
Chapter 7

• Population Concepts
• Population - a group of individuals of the same
  species occupying an area and capable of
  interacting with each other.
•  Natality - of individuals added to population
  through reproduction.
• birthrateborn per 1000 individuals per year
• Mortality - of individuals removed from
  population through death.
• deathratedie per 1000 individuals per year

2
Chapter 7

• Ability of a population to grow is a function of
•  sex ratio number of males to the number of
  females.
•  age distribution number of individuals in each
  age bracket 
• pre-reproductive age lt15
• reproductive age 15-44
• post-reproductive age gt44
• - survivorship curves
• - population pyramids

3
Chapter 7

• Population size influenced by dispersal 
• Movement from dense population to new areas
• emigration - outward migration
• Pressure (competition) is typical reason
  individuals leave a population.
• Typically juveniles leave, relieve overcrowding
•  immigration - inward migration
• Enter a population where pressure is less severe.
• Bring genetic/cultural characteristics

4
Chapter 7

• Population Growth Curve
• A populations inherent reproductive capacity is
  called its biotic potential.
• Plant versus animal 
• Typically, biotic potential is higher than that
  need to simply replace the parents.
• è most (many) offspring die, with few surviving
  to be reproductive adults.
•  
• Usually more than 2 survive.
• è population size grows.

5
Chapter 7

• Growth is typically exponential, until a stable
  size is reached.
• Lag phase
• It takes time for the first mating pairs to reach
  sexual maturity, mate, and produce offspring.
• Exponential growth phase
• As more and more individuals mature, more
  offspring are produced.
• Continues as long as birth rate exceeds death
  rate
• Stable equilibrium phase
• Birth rates and death rates become equal.
• Typically, death rate increases first. Often
  followed by a decrease in birth rate.

6
Chapter 7

• Carrying Capacity
• The number of individuals that can be supported
  in an area over time. Determined by
  environmental resistance.
• Limiting Factors
• Key components to limiting size of population
• availability of raw material
• availability of energy
• accumulation of waste products (can result in
  death phase)
• interactions between individuals
• If fix one, carrying capacity can increase, but
  new primary limiting factor emerges

7
Chapter 7

• K-strategist Start 2/25/02
• Have long lives, few offspring and provide much
  care for each offspring.
• Usually large organisms
• Strategy exert much energy into a few offspring
  that have a good chance of surviving.
• Exampleslion, deer, human
• Limited by density-dependent factors.
• Becomes more severe as size of population grows

8
Chapter 7

• r-strategist
• Have short lives, many offspring and provide
  little or no care for the offspring.
• Usually smaller organisms
• Strategy If only a very small percentage of
  offspring survive, produce MANY offspring.
• Examples frogs, fish, dandelions 
• Oyster may produce millions only couple survive
• Typically limited by density-independent factors
  and do not reach carrying capacity.
• Changing weather
• Pond dries up
• Destruction of food source

9
Chapter 7

• Human Population Growth
• Current rate of increase is 1.4.
• Current population size is around 6 billion.
• Very long lag time.
• Explosive growth in last 200 years.
• Currently in exponential growth phase
• Major reason for continuing increase is reduction
  in death rate
• Method of reduction shared throughout the world
• No change in birth rate

10
Chapter 7

• Environmental Resistance for Humans
• raw materials
• available energy
• waste disposal
• interactions with others 
• We will, with absolute certainty, reach our
  carrying capacity. What that level is, nobody
  knows. Earths population will double again by
  2050.