Biology - 16 Adaptations, Interdependence, and Competition - Required Practical 9: Field Investigations

Aims:

• measure the population size of a common species in a habitat

• use sampling techniques to investigate the effect of a factor on the distribution of this species

Risk Assessment:

Safety:

Equipment:

• 0.5 m x 0.5 m quadrat

• 2 surveyor tape measures

• random number generator

• (opt.) lux/light meter

Control variables:

• size of quadrat

• positions of measuring tapes

Investigating effect of a factor on distribution (example: light):

• other biotic and abiotic factors e.g.

  • herbivores

  • other plant species

  • roads and paths

Independent variable:

Dependent variable:

Method:

Estimating population:

1. Using the tape measures, create a 20 m x 20 m set of axis. This is the area we are estimating within

2. Use a random number generator to generate two numbers between 0 and 20. Use these coordinates to throw the quadrat

3. Count the number of the species being investigated within this quadrat and record

4. Repeat steps 2-3 10 times. If a repeat is generated, do not use it - generate another set of coordinates

Investigating effect of a factor on distribution (example: light):

1. Create a 30 m transect line using the measuring tape that goes from an area of low light intensity to one of high light intensity

2. Place the top right corner of the quadrat so it lines up with the 0 m on the measuring tape. Count the number of the species being investigated and record

3. At the top right corner of the quadrat, measure and record the light intensity using the lux meter

4. Repeat steps 2-3, moving in intervals of 5 m along the transect until you reach 30m

Calculations/graphing:

• to find total population:

  • find total area - 20 m x 20 m = 400 m²

  • find total investigated area - (0.5 m x 0.5 m) x 10 = 2.5 m²

  • divide total area by investigated area

  • multiply by total number of species counted

• graph light intensity against number of species counted