Population Biology

1
Population Biology

• AP Biology

Image taken without permission fron
http//www.earthinstitute.columbia.edu/e-newslette
r/2003/april03/SLElephantbyWater.jpg
2
How do you measure population size?

• Count all individuals
• Estimate population size by taking average
  density

3
How do you measure population size?

• Mark-Capture Method
• Capture a set of individuals (ex. 100) and tag
  them
• Set them free
• Return later and capture the same number of
  individuals (100)
• Determine how many in the second group are tagged
  ? divide original tagged by the number captured
  that are tagged the 2nd time
• Multiply this ratio by original tagged (100) to
  determine actual population

4
Example problem

• How many squirrels are living in McClellan Ranch
  Park?
• First time 100 squirrels captured and tagged
• Second time 100 squirrels captured, 50 are
  tagged
• What is the actual squirrel population size?

5
Solution

• Original population tagged 100
• Ratio 100 total / 50 tagged
• 2 (this means for every squirrel you
  tagged there was another one you didnt tag)
• 100 x 2 200
• The actual population is 200 squirrels

6
One more practice problem ?

• Determine the number of seagulls at Moonstone
  beach using the mark-capture method
• 150 seagulls captured and tagged at Moonstone
  Beach then set free
• 6 months later, another 150 are captured, this
  time 100 of them are already tagged.
• What is the actual seagull population size?

7
Solution

• Original population 150
• Ratio 150 total/ 100 tagged
• 1.5 (or 3/2)
• Actual population 150 x 1.5
• 225
  seagulls

8
Survivorship curves

• Tracks the number of individuals alive in a group
  (cohort) at each age.
• Type I low death rates in early and middle life
• Type II constant death rate over life span
• Type III high death rates in early life

9
Population growth

• Exponential growth
• Characterized by rapid growth in a very short
  period of time.
• Shows growth under ideal conditions (unlimited
  food, shelter, etc.)

10
Population growth

• Logistic growth
• A more realistic model of population growth
• A population will increase until it reaches
  carrying capacity
• Carrying capacity (K) maximum number of
  individuals in a population an environment can
  support

11
Question

• Can the carrying capacity change or is it a fixed
  number?
• Carrying capacity is NOT a fixed value it can
  depending on the conditions present (ex.
  Availability of food)

12
Reproductive Strategies

• r strategists
• Reproduce very quickly
• Have lots of offspring but a short life
  expectancy
• Little or no parental care
• Very small at birth
• Ex. mice, rabbits, weeds

• K strategists
• Prolonged development
• Have few young with longer lifespan
• Extensive parental care
• Larger at birth
• Ex. Elephants, tortoises, humans

13
Population Fluctuations

• Population sizes fluctuate as a result of
  interactions with other populations
• Predator/Prey Interactions
• The predator lags the prey changes in the
  predator population occur shortly after similar
  changes in prey population

14
(No Transcript)
15
GPS

• A method to track populations
• GIS (Geographic Information Systems)
• Computer Application (Arview to manipulate and
  view data)
• We will use this to continue our Tree Study at
  McClellan Ranch Park (field trip ?)

Images taken without permission
from www.colorado.edu/geography/
gcraft/notes/gps/gps.html