POPULATIONS RESPOND TO PRESSURES

1
POPULATIONS RESPOND TO PRESSURES

• Population Growth is Limited
• Birth, Death, Immigration Emigration
• Limiting Factors
• Effects of Population Density
• Populations have Distinct Reproductive Survival
  Strategies
• Reproduction is necessary for the survival of a
  species.
• Scientists observe patterns in the reproductive
  strategies used among species
• Opportunist strategies Competitor strategies

2
Birth/Death/Immigration/Emmigration

• Population Change
• (birth immigration) (death emigration)
• Immigration movement of individuals into a
  population (winds blowing plant seeds in)
• Emigration movement of individuals out of a
  population (some leave if resources get scarce)
• If a storm comes, a flock of seagulls may fly
  into a city dump and add to the existing
  population. Raccoons have been eating the
  seagull eggs there, so the immigrating birds
  could help stabilize the population or increase
  it (especially if some of the raccoons moved away)

3
Limiting Factors

• When birth rate is much higher than death rate,
  population grows rapidly eventually, population
  will stop growing due to lack of resources in
  habitat.
• Limiting Factor prevents the continuing growth
  of a population in an ecosystem.
• Abiotic (non-living) factors air, light, water.
• Biotic (living) factors other organisms in same
  habitat or same species in same area.
• Competition may occur between different
  populations or same populations in a habitat.
  (Deer growth in our area is making resources
  scarce for entire population)

4
Population Density Effects

• Density-dependent Factor limiting factor
  affecting a population when density is high
  (competition for food, disease-spreads easier in
  crowds). These have a greater effect as
  population grows.
• Density-independent Factor limiting factor
  having same effect on population whether high or
  low density. (Freezing temp., natural disasters,
  famine-no food available)

5
Opportunist Strategies

• Opportunists species that reproduce rapidly if
  their population falls below carrying capacity.
  Have
• Short life span usually ability to reproduce
  large quantities of offspring.
• Population size changes often live across many
  areas.
• Include algae, dandelions, bacteria, insects.
  All reproduce quickly move across area quickly.
• Can adapt quickly to environmental changes.

6
Competitor Strategies

• Competitor species with adaptations that allow
  them to remain at or near their carrying capacity
  for long period of time (different from other
  competitor who struggles with another to get
  resources).
• Often live longer have fewer offspring
  (elephants saguaro cacti). Offspring usually
  take longer to develop into adults so are cared
  for by parent longer.
• Not spread out over wide area as much, but more
  of offspring survive to reproductive age.