Specified Practical: Species Distribution & Abundance
- It is possible to investigate the factors that affect the abundance and distribution of organisms in a habitat; such factors might include:
- Light intensity
- Competition from other species
- The presence of a feature such as a road or stream
- Disturbance, e.g. from grazing or mowing
The effect of mowing on the abundance of daisies on a school field
Apparatus
- 2 long tape measures, e.g. 10 m
- A random number generator, e.g. a calculator, a phone or a set of dice
- 1 m2 quadrat
- A mowed and an unmowed area of grass within the school grounds
- An identification guide for common field plants
Method
- Lay out the two tape measures at right-angles to each other on a mowed section of the school field, creating a set of grid axes
- Use the random number generator to generate two random numbers to act as grid coordinates
- Lay the quadrat at the point at which the grid coordinates meet
- Using this system to place quadrats ensures that sample sites are chosen at random; this avoids bias and increases the likelihood that the sample results will accurately represent the area being sampled
- Count the number of daisy plants within the quadrat
- Include plants that fall more-than-half within the quadrat
- You may choose to count plants that are not in flower; a field guide can be used to identify the shape of the leaves in this situation
- Repeat steps 2-4 until you have values for at least 10 quadrats
- The larger the number of samples collected, the more representative the samples will be and the more likely it is that any conclusions will be valid
- The number of samples that are possible here may be limited by the time available
- Repeat steps 1-5 on an unmowed section of field
- Use the equation below to calculate an estimated population size for each field
Estimating abundance using a quadrat diagram
Quadrats can be placed at random grid coordinates to collect sample data for plant abundance on a school field
Analysis of results
- The sample data can be used to produce an estimate of the daisy population size for the mowed and unmowed fields as follows:
Population estimate = number of daisies in sample x (total area of field ÷ sample area)
Worked example
Students carried out fifteen 1 m2 quadrats on a 400 m2 area of mowed grass. They counted a total of 56 daises.
Population estimate = 56 x (400 ÷ 15)
= 1 493.3
= 1 493
Variables
- The independent variable here is whether or not the field has been mowed
- The dependent variable is the estimated daisy population for each field
- Control variables here might include:
-
- The time of year at which the samples are collected
- Soil type
- Light intensity
- Level of disturbance, e.g. from students using the field
- Note that some of these variables may be outside the control of a student, so you would need to be aware of the impact of the possible impact of these factors when drawing conclusions about the effect of mowing
-
Risk assessment
- A hazard in an experiment is something that could potentially harm you
- A risk is the harm that could occur as a result of the risk
- A control measure is the action taken to reduce the chance of the hazard causing a problem
Risk assessment for investigating species abundance practical table
Hazard | Risk | Control measure |
Plant thorns and stings | Cuts or stings on the skin |
Avoid touching plants while counting Learn to identify potentially harmful plants and avoid working with these species |
Uneven ground | Tripping or falling when walking between sample sites |
Wear practical footwear Pay attention while walking |