Question

A population of rabbits lives in a grassland ecosystem. Over several years, the rabbit population increases rapidly. Soon after, the rabbit population begins to decrease, even though predators have not increased.

Which factor is the most likely cause of the decrease in the rabbit population?

A. A decrease in genetic variation among the rabbit population
B. An increase in available food resources
C. Competition for limited resources such as food and space
D. An increase in the amount of sunlight reaching the grassland

2]

A population of fish lives in a freshwater pond. Over time, the amount of food in the pond remains constant, but the fish population increases until it stops growing and stays about the same size each year.

Which term best describes the maximum number of fish the pond can support?

A. Population density
B. Carrying capacity
C. Exponential growth
D. Trophic level

3]

A drought affects a grassland ecosystem, reducing plant growth. Soon after, populations of herbivores in the ecosystem begin to decrease.

Which factor most directly caused the decrease in the herbivore populations?

A. Increased predation by carnivores
B. Reduced availability of food
C. Increased genetic diversity
D. Increased reproduction rates

4]

A population of insects is introduced into a new environment with abundant food and no predators. The population increases rapidly at first, then slows as food and space become limited.

Which type of population growth does this scenario best represent?

A. Exponential growth followed by extinction
B. Random growth
C. Logistic growth
D. Linear growth

5]

The diagram shows an energy pyramid for a grassland ecosystem.

Grass at the bottom level
Rabbits above the grass
Snakes above the rabbits
Hawks at the top
Which statement best explains why only a small number of hawks can be supported in this ecosystem?

A. Hawks require less energy than organisms at lower trophic levels
B. Energy is lost as heat at each trophic level in the pyramid
C. Rabbits consume more energy than grass produces
D. Snakes prevent energy from reaching the hawks

Answer 1

1) C. Competition for limited resources such as food and space.
- The population likely reached carrying capacity; limited food/space caused density-dependent decline despite predator numbers staying the same.

2) B. Carrying capacity.
- The carrying capacity is the maximum population size the environment’s resources can sustain.

3) B. Reduced availability of food.
- Drought reduces plant growth, directly lowering food supply for herbivores and causing their populations to fall.

4) C. Logistic growth.
- Growth is rapid initially (exponential phase) then slows and levels off as resources become limited, which is the S-shaped logistic curve.

5) B. Energy is lost as heat at each trophic level in the pyramid.
- Only a small fraction of energy transfers to the next level, so less energy is available to support top predators like hawks.