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In an ecological study, a grasshopper population and that of crows was estimated in a certain grassland area over a period of one year. the results are as shown in the table below.

Number of adult
Grasshoppers x 102
Number of crows42018227211515
Amount of rainfall20055350520350121025190256350
  1. What is the relationship between the rainfall and grasshopper population?
  2. Account for the relationship stated in (1) above. 
  3. Explain the relationship between the grasshopper population and that of the crows.
  4. If the data was used in the construction of pyramid of numbers, what would be the trophic of;
    • Grasshoppers - 
    • Crows - 
    • The grass in the study area 
  5. If the area studied was one square kilometer, state:
    • one method that could have been used to estimate the crow population.
    • one method that could have been used to estimate the grasshopper population.
  6. Suggest what would happen if a predator for grasshoppers entered the study area.

1 Answer

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  1. High rainfall is followed a month later by high grasshopper population/low rainfall is followed a month later by low population of grasshoppers;
  2. vegetation/grass sprouts; vegetation/grass provide food for grasshoppers hence multiply rapidly; vegetation also offer shelter/camouflage for grasshoppers hence predators do not spot them easily;
  3. Presence of large number of grasshopper is associated with large number of crows in the same month; The crows feeding on grasshopper/predating on the grasshopper; if grasshopper population is low the crow population decrease due to migration to other areas in search of alternative food (sources);
    • Grasshoppers - 2nd  (trophic) level/ primary consumers;
    • Crows - 3rd  (trophic) level/secondary consumers;
    • The grass in the study area -  1st (trophic) level/producers;
    • Total count;
    • Capture re-capture;
  6. Vegetation/grass would sprout/increase due to decrease of grasshoppers; The predator would compete for food/grasshoppers with the crows (causing  some grasshoppers to migrate) rapidly declining grasshopper population;

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