Ecological Sampling & Diversity Data — Practice · Grade 12 Science

Chapter: Ecology, Populations & Biodiversity

What this practice covers

By the end of Ecological Sampling & Diversity Data you should be able to:

8 questions, numeric and written answer, each with a worked explanation.

Vocabulary used: quadrat, richness, evenness.

Problem 1

20 individuals in 5 m² gives what density?
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

4 individuals/m²

20/5=4.

Problem 2

Why randomize quadrat placement?
Answer and explanation

To reduce selection bias and improve representativeness for the defined habitat.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

Two species have fractions .4 and .6. Find D=1−Σpi².
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

0.48

1−(.16+.36)=.48.

Problem 4

Why is one large total count not a complete sampling description?
Answer and explanation

Area, effort, detectability, locations, and timing determine its interpretation.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

Five equal 2 m² quadrats contain 30 plants total. Find density. Show the reasoning, not just the conclusion.
Hints

Patchiness and selection method affect uncertainty and representativeness.

Answer and explanation

30/10=3 plants/m².

Problem 6

Why should a mark–recapture estimate state assumptions?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Movement, survival, marking effects and mixing can bias estimates if the model's conditions fail.

Problem 7

Density divides total count by the actual sampled areaDensity divides total count by the actual sampled areaQuadratAreaIndividualsA0.25 m²3B0.25 m²5C0.25 m²4Density=12/0.75=16 individuals/m²Mean count per quadrat is 4, not 4 individuals/m².
Illustrative quadrat records with explicit areas; no extrapolated field total is asserted.
Interpret the supplied visual. If the same 12 individuals came from three 1 m² quadrats, what density would result?
Answer and explanation

4 individuals/m²; the sampled area changes the denominator.

Density is individuals per area or volume, not merely an average count per container. Three 0.25 m² quadrats totaling 12 individuals cover 0.75 m², giving 16 individuals/m². A whole-field abundance estimate multiplies by a relevant area only if representativeness is justified. Use total sampled area when quadrat sizes differ, and avoid treating a handful of plots as an exact census. Report variability and selection limits alongside the estimate.

4 individuals/m²; the sampled area changes the denominator.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

Four 0.50 m² quadrats contain 2,4,6,4 individuals. Find pooled density and an abundance estimate for 100 m² if sampling is representative; state why it is an estimate.
Answer and explanation

Total 16 over 2.0 m² gives 8 individuals/m². Extrapolated abundance≈800. Spatial variation, finite sampling and imperfect detection make it an estimate rather than a census.

Total 16 over 2.0 m² gives 8 individuals/m².

Extrapolated abundance≈800.

Spatial variation, finite sampling and imperfect detection make it an estimate rather than a census.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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