IB ESS SL 2.1.15 Estimating Population Abundance Questions
Practise IB ESS SL 2.1.15 by choosing sampling methods, estimating population abundance and evaluating uncertainty in ecological data.
- Syllabus
- First assessment 2026
- Course
- ESS SL
- Level
- SL
Exam points
- choose and describe random, systematic or transect sampling for named sessile or mobile populations
- estimate abundance from quadrats, transects, aerial or camera observations or mark-release-recapture
- repeat baselines and standardise sampling to detect abundance change over time or after human activity
- interpret samples to support conclusions about abundance, richness, distribution or population change
- evaluate uncertainty using detectability, movement, identification, bias, extrapolation, season and replication
IB ESS SL 2.1.15 Estimating Population Abundance Questions question 1
[Maximum number: 9]
To what extent can the practical strategies for obtaining data for a pyramid of numbers be made reliable?
Answers may demonstrate:
- understanding concepts & terminology of reliability in sampling; quadrats (including number, size, positioning, species distribution); transects; aerial photographs; traps; nets; Lincoln index; mark/release/recapture (including issues of marking technique, trap-happy and trap shy phenomena, time interval); aquatic sampling use of dragnets, kick samples); camera traps (difficulty of extrapolation); general sampling issues (including repetition; extrapolation; seasonal variation; randomisation); total census; abundance; bias; scientific expertise; etc.
- breadth in addressing and linking different sampling methodologies with varying degree of reliability for a range of different sessile and motile populations in a range of different habitats;
- examples of named sampling methods appropriate for different named species etc.
- balanced analysis evaluating extent to which sampling method can be executed to produce reliable data; practical issues hindering application of methodologies in the field.
- a conclusion that is consistent with, and supported by analysis and examples given e.g. All methods of sampling inevitably involve a degree of inaccuracy compared with a total census, but they can always be made more reliable by repeated executions.
The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria in each of the markbands (although ESS terminology has been conflated with "understanding concepts"). This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.
Section B, part (c) markbands
0: The response does not reach a standard described by the descriptors below and is not relevant to the question.
1–3: The response contains:
• minimal evidence of knowledge and understanding of ESS issues or concepts
• fragmented knowledge statements poorly linked to the context of the question
• some appropriate use of ESS terminology
• no examples where required, or examples with insufficient explanation/relevance
• superficial analysis that amounts to no more than a list of facts/ideas
• judgments/conclusions that are vague or not supported by evidence/argument.
4–6: The response contains:
• some evidence of sound knowledge and understanding of ESS issues and concepts
• knowledge statements effectively linked to the context of the question
• largely appropriate use of ESS terminology
• some use of relevant examples where required, but with limited explanation
• clear analysis that shows a degree of balance
• some clear judgments/conclusions, supported by limited evidence/arguments.
7–9: The response contains:
• substantial evidence of sound knowledge and understanding of ESS issues and concepts
• a wide breadth of knowledge statements effectively linked with each other, and to the context of the question
• consistently appropriate and precise use of ESS terminology
• effective use of pertinent, well-explained examples, where required, showing some originality
• thorough, well-balanced, insightful analysis
• explicit judgments/conclusions that are well-supported by evidence/arguments and that include some critical reflection.
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