WCAS - Washington Comprehensive Assessment of Science Ecosystems: Interactions and Dynamics Questions and Answers

Question 1

In a forest ecosystem, the removal of wolves, a top predator, leads to a dramatic increase in the deer population. This, in turn, causes overgrazing of aspen trees, significantly reducing their numbers. This entire chain of events is an example of:

Accepted Answer

A trophic cascade

Answer

A trophic cascade is an ecological phenomenon triggered by the addition or removal of top predators, which results in reciprocal changes in the populations of predator and prey through a food chain. In this scenario, removing the wolves (top predator) directly impacts the deer (primary consumer), which then impacts the aspen trees (producer).

Question 2

A small island ecosystem can support a maximum population of 500 seabirds due to limited nesting sites and food resources. If the seabird population grows to 600 individuals, which of the following is the MOST likely outcome?

Accepted Answer

The population will experience a decline due to density-dependent limiting factors.

Answer

The carrying capacity is the maximum population size an environment can sustain. When a population exceeds its carrying capacity, density-dependent limiting factors like competition for food, increased disease transmission, and lack of space will lead to a decrease in the population size until it returns to a sustainable level.

Question 3

The relationship between a clownfish and a sea anemone is a classic example of mutualism. The clownfish is protected from predators by the anemone's stinging tentacles, to which it is immune. In return, the clownfish cleans the anemone and provides nutrients through its waste. Which of the following best describes this type of interaction?

Accepted Answer

A symbiotic relationship where both species benefit.

Answer

Mutualism is a type of symbiotic relationship where both organisms involved benefit from the interaction. The clownfish gains protection, and the sea anemone receives cleaning and nutrients. Since both species derive a benefit, it is a mutualistic symbiotic relationship.

Question 4

A certain pesticide is sprayed on crops to control insects. This pesticide is persistent and accumulates in the fatty tissues of organisms. Which organism in the following food chain would be expected to have the highest concentration of this pesticide: Grass -> Grasshopper -> Shrew -> Owl?

Accepted Answer

Owl

Answer

This scenario describes biomagnification, the process where the concentration of a toxin increases at successively higher levels in a food chain. The owl, as the apex predator at the top of this food chain, consumes many shrews, each of which has consumed many grasshoppers. The toxin accumulates at each trophic level, resulting in the highest concentration in the owl.

Question 5

Sea otters are a crucial component of the kelp forest ecosystem. They prey on sea urchins, which in turn feed on kelp. Without sea otters, sea urchin populations explode, leading to the destruction of the kelp forests that provide habitat for numerous other species. Because of their disproportionately large effect on the ecosystem relative to their abundance, sea otters are considered a(n):

Accepted Answer

Keystone species

Answer

A keystone species is an organism that has a disproportionately large effect on its environment relative to its abundance. The sea otter's role in controlling the sea urchin population is critical for the health and stability of the entire kelp forest ecosystem, making it a classic example of a keystone species.

WCAS - Washington Comprehensive Assessment of Science Practice Test

WCAS - Washington Comprehensive Assessment of Science Practice Test

WCAS - Washington Comprehensive Assessment of Science Ecosystems: Interactions and Dynamics Questions and Answers