Biodiversity & Ecosystem Services — Drills · Grade 12 Science

Chapter: Ecology, Populations & Biodiversity

What these drills covers

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

6 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

The variety of different ecosystems and habitats across a landscape is called
  1. genetic diversity
  2. species evenness
  3. ecosystem diversity
  4. species richness
Answer and explanation

ecosystem diversity

Ecosystem diversity is the variety of habitats and ecological communities in a region.

Problem 2

Which of these is a provisioning ecosystem service?
  1. climate regulation
  2. natural pest control
  3. recreation and scenic beauty
  4. food and timber production
Answer and explanation

food and timber production

Provisioning services supply tangible goods like food and timber.

Problem 3

A field sample has three plant species with 50, 30, and 20 individuals (N = 100). Calculate Simpson's Diversity Index, D = 1 - Σ(n/N)².
Answer and explanation

0.62

(0.50)² + (0.30)² + (0.20)² = 0.25 + 0.09 + 0.04 = 0.38; D = 1 - 0.38 = 0.62.

Problem 4

Removing sea otters lets sea urchins multiply and destroy kelp forests, collapsing local diversity. This makes the sea otter a
  1. keystone species
  2. primary producer
  3. density-independent factor
  4. decomposer
Answer and explanation

keystone species

Its removal reshapes the whole community out of proportion to its abundance — the mark of a keystone species.

Problem 5

Two communities have the same number of species. Explain how one can still be more diverse than the other.
Answer and explanation

Diversity depends on evenness as well as richness. If one community's individuals are spread evenly among its species while the other is dominated by a single species with a few rare ones, the more even community has higher diversity (a higher Simpson's index), even though both have the same number of species.

Problem 6

A restored prairie has five plant species, each with 20 individuals (N = 100). Calculate Simpson's Diversity Index, D = 1 - Σ(n/N)².
Answer and explanation

0.8

Each proportion is 0.20; Σ(n/N)² = 5 × (0.20)² = 5 × 0.04 = 0.20; D = 1 - 0.20 = 0.80.

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