SAT - Biology Subject Population and Community Ecology Questions and Answers — Questions and Answers
Question 1: A population of deer is introduced to a large, isolated island with abundant resources and no predators. Initially, the population grows rapidly. According to the logistic growth model, what will happen to the population's growth rate as it approaches the island's carrying capacity (K)?
- The growth rate will become negative, causing a population crash.
- The growth rate will continue to increase exponentially.
- The growth rate will slow down and approach zero. (Correct answer)
- The growth rate will remain constant at its maximum.
Correct answer: The growth rate will slow down and approach zero.
In the logistic growth model, population growth is density-dependent. As the population size (N) nears the carrying capacity (K), limiting factors such as resource scarcity and increased competition cause the per capita growth rate to decrease. When N equals K, the birth rate equals the death rate, and the population growth rate becomes zero. [9, 11, 17]
Question 2: The harmless scarlet kingsnake has coloration and banding patterns that closely resemble those of the venomous eastern coral snake. Predators that have learned to avoid the coral snake will also avoid the kingsnake. This is an example of which ecological phenomenon?
- Batesian mimicry (Correct answer)
- Müllerian mimicry
- Aposematic coloration
- Cryptic coloration
Correct answer: Batesian mimicry
Batesian mimicry is a form of defense in which a harmless species evolves to imitate the warning signals of a harmful or unpalatable species. [7, 12, 16] The kingsnake (mimic) benefits from the predator's learned avoidance of the coral snake (model). Müllerian mimicry involves two or more harmful species resembling each other.
Question 3: Which of the following sets of characteristics is most representative of a K-selected species?
- Short lifespan, early maturation, many offspring
- Unstable environment, rapid population growth, little parental care
- Large body size, few offspring, short lifespan
- Long lifespan, extensive parental care, few offspring (Correct answer)
Correct answer: Long lifespan, extensive parental care, few offspring
K-selected species are adapted to stable environments and live at densities near the carrying capacity (K). Their life history strategy involves traits like having a long lifespan, maturing late, producing few, large offspring, and providing extensive parental care to ensure high offspring survival. [1, 2, 5, 6]
Question 4: An oyster releases millions of eggs, but the vast majority of the resulting larvae die from predation or starvation within their first few weeks of life. The few larvae that survive to adulthood have a much lower mortality rate. Which type of survivorship curve does the oyster exhibit?
- Type I
- Type III (Correct answer)
- Type II
- Type IV
Correct answer: Type III
A Type III survivorship curve is characterized by a very high mortality rate for the young, followed by a flatting curve indicating a much lower mortality rate for those individuals who survive to a certain age. This is typical for species that produce a large number of offspring and provide little to no parental care. [8, 23, 29, 30]
Question 5: In the coastal kelp forest ecosystems of the North Pacific, sea otters prey on sea urchins. Sea urchins, if left unchecked, will graze voraciously on kelp, destroying the forests that provide habitat for numerous other species. The sea otter's role in maintaining the structure of this community is best described as that of a(n):
- Indicator species
- Foundation species
- Keystone species (Correct answer)
- Apex predator
Correct answer: Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. By controlling the sea urchin population, sea otters prevent the destruction of kelp forests and thereby maintain the entire community's structure and biodiversity. [4, 13, 18, 22] While they are also apex predators, the term "keystone species" specifically describes this critical ecological role.
Question 6: Which of the following scenarios is the best example of a uniform population distribution?
- Nesting seabirds on a crowded island, where each bird defends the area immediately around its nest. (Correct answer)
- A school of fish swimming together to avoid predators.
- Dandelion plants in a field, where seeds have been scattered by the wind.
- Elephants and other large mammals congregating around a desert waterhole.
Correct answer: Nesting seabirds on a crowded island, where each bird defends the area immediately around its nest.
A uniform distribution, where individuals are evenly spaced, typically results from antagonistic social interactions, such as territoriality. [10, 19, 20, 27] Nesting seabirds actively defend their territory, which creates a regular pattern of spacing. The other options describe clumped (fish, elephants) or random (dandelions) distributions.
