2.8.2Additional lessons
Abiotic Factors and Species Distribution — IB Biology SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 42 of 142
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 6Abiotic Factors
Temperature
- Temperature Affects enzyme activity and the rate of metabolic reactions, so each species has a range it can survive.
Water
- Water Availability of water controls survival for terrestrial species, especially plants, and salinity matters in water.
Light
- Light Light intensity limits photosynthesis, so producers are found where enough light is available.
Soil and pH
- Soil and pH Soil pH, nutrients and drainage determine which plants can grow, and these in turn affect animals.
Oxygen and wind
- Oxygen and wind Dissolved oxygen limits aquatic animals, while strong wind increases water loss and damages plants.
Part 2 of 6Tolerance Range
1
Every species can only survive between a minimum and a maximum value of each abiotic factor.
2
Within the range there is an optimum zone where growth and reproduction are best.
3
Toward the edges lies a zone of stress, where organisms survive but few reproduce.
4
Beyond the limits of tolerance the species cannot survive, so it is absent from the area.
5
The abiotic conditions in a habitat therefore decide where each species can be found.
Part 3 of 6Distribution
Distribution
Abundance
- Abundance A species is most abundant where conditions are close to its optimum for the abiotic factors.
Absence
- Absence A species may be missing from a suitable area because of barriers, competitors or predators.
Biotic factors
- Biotic factors Predation, competition, disease and food supply also influence the distribution of species.
Correlation
- Correlation A match between a species' distribution and a factor suggests a link, but it needs experimental testing.
Part 4 of 6Investigating a Factor
Investigating a Factor
Gradient
- Gradient Measure an abiotic factor at several points along a transect and record the species present at each.
Experiment
- Experiment Grow the species at different values of the factor, controlling all others, to find its tolerance range.
Data
- Data Plot abundance against the factor to identify the optimum and the limits of tolerance.
Part 5 of 6Worked Illustration
Worked Illustration
Soil pH
- Soil pH A plant that tolerates only a narrow pH range will be found only on soils within that range.
Salinity
- Salinity Few freshwater species survive in sea water, since their cells would lose water by osmosis.
Light
- Light In a forest, plants of the ground layer are restricted to areas where enough light reaches them.
Part 6 of 6Exam Checklist & Tips
2.8.2 – Key Points for the Exam
- Abiotic factor A non-living physical or chemical part of the environment.
- Tolerance range The range of values of an abiotic factor within which a species can survive.
- Optimum The value of a factor at which a species grows and reproduces best.
- Distribution Where in an area a species is found.
Common Mistakes
- Saying that organisms die immediately outside the optimum;
- they survive but are stressed within the tolerance range.
- Assuming that only abiotic factors control distribution, ignoring competitors and predators.
- Describing temperature as a biotic factor.
- Claiming that a correlation proves one factor causes the distribution.
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