WCAS - Washington Comprehensive Assessment of Science Ecosystems: Interactions and Dynamics Questions and Answers — 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:
- Competitive exclusion
- A trophic cascade (Correct answer)
- Primary succession
- Biomagnification
Correct answer: A trophic cascade
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?
- The island's carrying capacity will permanently increase to 600.
- The population will experience a decline due to density-dependent limiting factors. (Correct answer)
- The birds will evolve to require fewer resources.
- Other species will immigrate to the island to support the larger population.
Correct answer: The population will experience a decline due to density-dependent limiting factors.
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?
- Parasitism, where one organism benefits and the other is harmed.
- Commensalism, where one organism benefits and the other is unaffected.
- A predator-prey relationship where the clownfish is the prey.
- A symbiotic relationship where both species benefit. (Correct answer)
Correct answer: A symbiotic relationship where both species benefit.
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?
- Grasshopper
- Shrew
- Owl (Correct answer)
- Grass
Correct answer: Owl
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):
- Invasive species
- Producer
- Keystone species (Correct answer)
- Decomposer
Correct answer: Keystone species
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.
Question 6: Which of the following describes a density-independent limiting factor that could affect a population of deer in a forest?
- A sudden, severe forest fire that burns a large area. (Correct answer)
- An outbreak of a contagious disease that spreads quickly among the deer.
- Increased competition for a limited supply of acorns during the winter.
- A rise in the population of wolves, the primary predator of the deer.
Correct answer: A sudden, severe forest fire that burns a large area.
Density-independent factors affect a population regardless of its size or density. A forest fire is a catastrophic event that will impact the deer population whether it is large or small. The other options—disease, competition, and predation—are density-dependent factors, as their effects become more pronounced as the population density increases.
WCAS - Washington Comprehensive Assessment of Science Ecosystems: Interactions and Dynamics Questions and Answers
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: