Download - P p population growths #4(1)
4 Important characteristics of Populations
• 1. GEOGRAPHICAL
DISTRIBUTION– Area that is inhabited
by a population
• Varies in size from a few cm3 (bacteria) to millions of square kilometers
2. Density of Area
• # of individuals per unit area
• Ex: desert cactus = low density
• Cactus brush = high density
Partner activity: Density & Growth Rate
• Density formula = # of indiv/area
• 1. What is the density of 150 bullfrogs in
a pond that covers an area of 3 sq.
km?
50 bullfrogs/sq. km
Growth Rate
• Pf - Pi = Growth Rate **can be a neg.
∆Time number
1. In 1940, 4,800 sea otters were counted in a field study off the coast of Monterey, Calif. The field study continued until 1945 when scientists counted only 2,200 sea otters. What was the growth rate of sea otters?
2. -520 sea otters/year
More Problems
• In the Fall of 2000, there were 1857 students at RAHS. This fall in 2008 the student count was 2,164. Growth rate?
• 38 students/year
3. Growth Rate (factors that affect populations
• 1. Number of births (natality)
• 2. Number of deaths
(mortality)
4. # of members that enter or leave the population
• Immigration = movement of individuals into an area
• Emigration = movement of individuals out of an area
Limiting Factors (affecting Populations Growth)
• Competition for• water• shelter• food• Predation• Parasitism & disease• Drought & climate
change• Human disturbances
More Later
Graphs that represent Growth Rates
Exponential Growth (J-curve)
LAG PHASE
EXPONENTIAL PHASE
Exponential Growth
• Occurs when a population reproduces at a constant rate.
• At 1st, growth is slow
• Under ideal conditions with unlimited resources, pop. will grow exponentially
Partner Activity• Example: bacteria
– Within 20 min. bacteria will divide & reproduce asexually
– If an area starts with 2 bacteria cells on it, how many bacteria will have grown in 3 hours?
ANSWER = 1024
Logistic Growth (S-curve)
Logistic Growth• As a resource becomes less available, populations
slows or stops
LAG PHASE
EXPONENTIAL PHASE
STABILIZATION PHASE
CARRYING CAPACITY
Predator-Prey Graph
Predator-prey Graph
• The best known mechanism of pop.control
• Pattern can repeat indefinitely
Extinction Graph
Extinction
• Usually occurs:– After a catastrophic
disaster • Asteroid impacts(?)• Fire• flood
Terms to Know• Carrying capacity - the largest # of indiv. That an
environment can support.
EXPONENTIAL PHASE
STABILIZATION PHASE
• Stabilization phase – population has meet its carrying capacity and population growth levels off
• Exponential growth – a population that reproduces at a constant rate