2.9.3Inquiry Process
Species Distribution- Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 94 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 6Why Sample and What Distribution Means
A transect is a way of sampling along an environmental gradient.
Distribution
- Distribution Where a species is found within an ecosystem, which is influenced by limiting factors that may be abiotic or biotic.
Sampling
- Sampling Taking measurements from small areas to represent a large habitat, because counting every individual organism would take far too long.
Representative sample
- Representative sample The sample must be large enough and taken fairly so that it reflects the whole habitat, otherwise conclusions will be unreliable.
Environmental gradient
- Environmental gradient A gradual change in an abiotic factor across a habitat, such as soil water content rising with nearness to a stream.
Part 2 of 6Types of Transect
Continuous line transect
- Continuous line transect A tape is laid along the gradient and every species touching the tape is recorded along its whole length.
Interrupted line transect
- Interrupted line transect Only species touching the tape at regular intervals, for example every metre, are recorded, which saves time.
Continuous belt transect
- Continuous belt transect Quadrats are placed end to end along the tape so the whole strip is sampled and abundance is measured throughout.
Interrupted belt transect
- Interrupted belt transect Quadrats are placed at regular intervals, such as one every metre, which is quicker but samples only part of the strip.
| Transect | Sampling | Speed |
|---|---|---|
| Continuous line | Whole length of line | Slow |
| Interrupted line | Points at intervals | Faster |
| Continuous belt | Quadrats end to end | Slowest, most detail |
| Interrupted belt | Quadrats at intervals | Faster |
Part 3 of 6Measuring Abiotic Factors
Measuring Abiotic Factors
Choose relevant factors
- Choose relevant factors Measure only abiotic factors that matter to the question;
- water turbidity, for example, is not relevant in a woodland.
Sensors and meters
- Sensors and meters Air temperature uses a thermometer, light intensity a light meter, dissolved oxygen an oxygen sensor, and rainfall a rain gauge.
Soil water content
- Soil water content Weigh a soil sample, dry it, weigh it again, and use the loss in mass as a measure of the water it held.
Slope and aspect
- Slope and aspect A clinometer gives the angle of a slope and a compass gives the direction in which a site faces.
Kite diagram
- Kite diagram Width of each kite shows abundance of a species at a point along the transect, while the centre line shows its presence and position.
Part 4 of 6Interpreting Results
1
Mark out the transect along the gradient and decide the sampling interval before starting.
2
At each sample point record abundance of each species and measure the abiotic factor with the same equipment each time.
3
Repeat the investigation in more than one place so that results are reliable and anomalies can be spotted.
4
Draw a kite diagram with distance along the transect on the x-axis and extra sections for the abiotic factor.
5
Link the position of each species to the abiotic values, and state whether the pattern suggests a limiting factor.
Part 5 of 6Worked Example
Question
- Soil water was measured at one sample point.
- A soil sample had a mass of 52.0 g when fresh and 41.6 g after drying to constant mass.
- Calculate the percentage of water in the fresh sample.
- Mass of water lost = 52.0 - 41.6 = 10.4 g.
- Percentage water = 10.4 / 52.0 x 100.
- 10.4 / 52.0 = 0.20, so the percentage is 20%.
Answer The fresh soil sample contained 20% water by mass.
Part 6 of 6Exam Checklist & Tips
2.9.3 – Key Points for the Exam
- Transect A line laid across a habitat along which organisms are sampled.
- Quadrat A square frame placed on the ground to sample the organisms inside it.
- Kite diagram A graph showing distribution and abundance of species along a transect.
- Clinometer An instrument used to measure the angle of a slope.
- Abundance The number or amount of a species present in an area.
Common Mistakes
- Placing quadrats where the plants look interesting instead of at the planned intervals, which introduces bias.
- Measuring the abiotic factor only once for the whole transect instead of at every sample point.
- Drawing kite diagrams with uneven widths on each side of the centre line; the kite must be symmetrical.
- Concluding that a factor causes a distribution from a single transect; correlation is not proof of cause.
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