GATE Ecology & Ecosystem Science: practice questions

GATE — Ecology and Evolution (EY) · India · IITs and IISc on rotation

Original practice questions written to the published syllabus · not past papers

6worked here, free

26written to this exam in this subject

9syllabus units

What this subject covers

How organisms, populations, communities and ecosystems work: energy flow, productivity, nutrient cycles, succession and population dynamics. Every sustainability argument eventually rests on this subject.

In the exams: GATE ES Section 8 (ecology and ecosystems); ICAR AICE subject 71 Unit 1; UGC NET Environmental Sciences Unit 3 (environmental biology); GATE EY core

Levels of ecological organisation; autecology and synecology
Habitat, niche and the competitive exclusion principle
Population characteristics: density, natality, mortality, age structure
Population growth: exponential, logistic, r- and K-selection
Species interactions: competition, predation, mutualism, parasitism
Community structure, diversity and dominance
Ecological succession: primary, secondary, climax concepts
Ecosystem structure and function; trophic levels, food chains and webs
Energy flow, ecological efficiency and ecological pyramids
Primary and secondary productivity
Biogeochemical cycles: carbon, nitrogen, phosphorus, sulphur, water
Biomes of the world: forest, grassland, desert, tundra, aquatic
Agroecosystems compared with natural ecosystems
Stability, resistance and resilience of ecosystems

What GATE asks from it

GATE — Ecology and Evolution (EY) and Environmental Science (Section 8)

Population growth models and their parameters, life tables and survivorship, mark–recapture, competition and predator–prey models, diversity indices and similarity, island biogeography, energy flow efficiencies, productivity and cycles, with numerical answer type questions.

Where the 26 questions fall

How our questions for GATE spread across the units of Ecology & Ecosystem Science. Difficulty: 0 easy, 11 medium, 15 hard.

Population growth: exponential, logistic, r- and K-selection	7
Community structure, diversity and dominance	5
Habitat, niche and the competitive exclusion principle	4
Population characteristics: density, natality, mortality, age structure	3
Species interactions: competition, predation, mutualism, parasitism	2
Stability, resistance and resilience of ecosystems	2
Ecological succession: primary, secondary, climax concepts	1
Ecosystem structure and function; trophic levels, food chains and webs	1
Energy flow, ecological efficiency and ecological pyramids	1

6 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

1 · Population growth: exponential, logistic, r- and K-selection · medium

For logistic growth dN/dt = rN(1 − N/K) with r = 0.4 per year and K = 1000, what is the growth rate when N = 500?

400 per year
200 per year
40 per year
100 per year

Answer and working

D. 100 per year

dN/dt = 0.4 × 500 × (1 − 0.5) = 100 per year, the maximum, since it occurs at K/2.

Further reading: See the manual sources: standard ecology textbooks (Odum, Begon et al., Krebs) and the original studies named in the explanation

2 · Population growth: exponential, logistic, r- and K-selection · medium

In the logistic model, at what population size is the growth rate (dN/dt) greatest?

At 2K
At K/2
At zero
At K

Answer and working

B. At K/2

dN/dt = rN(1 − N/K) peaks at N = K/2, the basis of maximum sustainable yield.

Further reading: See the manual sources: standard ecology textbooks (Odum, Begon et al., Krebs) and the original studies named in the explanation

3 · Population growth: exponential, logistic, r- and K-selection · hard

A fish stock follows logistic growth with r = 0.6 per year and K = 2000 tonnes. What is its maximum sustainable yield?

150 tonnes per year
1200 tonnes per year
300 tonnes per year
600 tonnes per year

Answer and working

C. 300 tonnes per year

MSY = rK/4 = 0.6 × 2000 ÷ 4 = 300 t/yr, at a stock of K/2 = 1000 t. 1200 is rK; 600 is rK/2; 150 slips a factor of two.

Further reading: See the manual sources: standard ecology textbooks (Odum, Begon et al., Krebs) and the original studies named in the explanation

4 · Population growth: exponential, logistic, r- and K-selection · hard

Why is harvesting at the estimated maximum sustainable yield considered risky?

MSY applies only to plants, not to fish or wildlife populations
r and K are uncertain, so estimated-MSY harvests risk decline
Harvesting at MSY guarantees that the stock grows beyond K each year
MSY is always far below the level at which stocks begin to decline

Answer and working

B. r and K are uncertain, so estimated-MSY harvests risk decline

Estimation errors and environmental variability mean MSY-based harvests have led to collapses; precautionary reference points are used instead.

Further reading: See the manual sources: standard ecology textbooks (Odum, Begon et al., Krebs) and the original studies named in the explanation

5 · Ecological succession: primary, secondary, climax concepts · hard

Which mechanism of succession, in Connell and Slatyer's (1977) models, involves early species making conditions more suitable for later species?

Tolerance
Competitive exclusion
Facilitation
Inhibition

Answer and working

C. Facilitation

In facilitation early colonists modify the environment (for example building soil) to aid later species; tolerance and inhibition work differently.

Further reading: See the manual sources: standard ecology textbooks (Odum, Begon et al., Krebs) and the original studies named in the explanation

6 · Stability, resistance and resilience of ecosystems · medium

What did David Tilman's Cedar Creek grassland experiments show?

Diverse plots had steadier biomass and resisted drought
Diverse plots collapsed completely during drought
Species number had no effect on any ecosystem property
Plots with fewer species were always more stable in every year

Answer and working

A. Diverse plots had steadier biomass and resisted drought

Higher diversity stabilised community biomass and improved drought resistance, consistent with the insurance hypothesis.

Further reading: See the manual sources: standard ecology textbooks (Odum, Begon et al., Krebs) and the original studies named in the explanation

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