Biodiversity & Ecosystem Services — Practice · Grade 12 Science

Chapter: Ecology, Populations & Biodiversity

What this practice covers

By the end of Biodiversity & Ecosystem Services you should be able to:

9 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: biodiversity, genetic diversity, species diversity, ecosystem diversity, ecosystem services, keystone species.

Problem 1

Which of these is an example of genetic diversity?
  1. The variety of alleles for coat color within a single wolf population
  2. The range of ecosystems found across a continent
  3. The total biomass of producers in a field
  4. The number of different bird species in a forest
Answer and explanation

The variety of alleles for coat color within a single wolf population

Genetic diversity is variation within a species or population, such as different coat-color alleles in one wolf population.

Problem 2

A wetland that naturally filters pollutants out of water is providing which type of ecosystem service?
  1. Cultural
  2. Regulating
  3. Genetic
  4. Provisioning
Answer and explanation

Regulating

Purifying water is a regulating service — the ecosystem stabilizes and improves environmental conditions.

Problem 3

A pond sample has two fish species with 30 and 70 individuals (N = 100). Calculate Simpson's Diversity Index, D = 1 - Σ(n/N)².
Answer and explanation

0.42

(0.30)² + (0.70)² = 0.09 + 0.49 = 0.58; D = 1 - 0.58 = 0.42.

Problem 4

A sea star preys on mussels that would otherwise crowd out other shoreline species. Removing the sea star causes local diversity to collapse. The sea star is best described as a
  1. invasive species
  2. decomposer
  3. keystone species
  4. producer at the base of the food web
Answer and explanation

keystone species

Its impact is far greater than its abundance, and its removal reshapes the whole community — the definition of a keystone species.

Problem 5

Explain how high genetic diversity within a species can make that species more likely to survive a new disease.
Answer and explanation

With many different alleles present, it is more likely that at least some individuals happen to carry genes that resist the disease. Those individuals survive and reproduce, so the population persists, whereas a genetically uniform population could be wiped out all at once.

Problem 6

Why compare evenness as well as richness in communities? Show the reasoning, not just the conclusion.
Hints

Use a service-specific measure and sampling design.

Answer and explanation

Equal richness can hide strong dominance differences and altered functioning.

Problem 7

A service improves after restoration. What evidence helps attribute the improvement?
Hints

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

Answer and explanation

Baseline and comparison data, consistent methods and a mechanism linking restoration to the measured service.

Problem 8

State the exact diversity-index convention before calculatingState the exact diversity-index convention before calculatingSpeciespi in Xpi²A0.250.0625B0.250.0625C0.250.0625D0.250.0625D=1−Σpi²=1−0.25=0.75
Original index calculation from illustrative proportions, with explicit formula and no finite-sample correction.
Interpret the supplied visual. Find D for two species with fractions 0.8 and 0.2.
Answer and explanation

D=1−(0.64+0.04)=0.32 under the stated convention.

For this course, the selected Simpson diversity convention is D=1−Σpi², with pi the observed fraction in species i. Larger values mean greater diversity under this convention. Other publications use the sum or its reciprocal, so the name alone is ambiguous. For four equally common species D=0.75. The result is an estimate from sampled counts and does not identify habitat quality, extinction risk or causal mechanisms by itself.

D=1−(0.64+0.04)=0.32 under the stated convention.

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 9

Counts are 6,3,1 for three species. Find richness and D=1−Σpi², then state a sampling limitation.
Answer and explanation

Richness=3. Fractions 0.6,0.3,0.1 give D=1−(0.36+0.09+0.01)=0.54. The sample may miss rare or hard-to-detect species; matched effort and replication matter.

Richness=3.

Fractions 0.6,0.3,0.1 give D=1−(0.36+0.09+0.01)=0.54.

The sample may miss rare or hard-to-detect species; matched effort and replication matter.

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.

Browse all courses