GRE Subject Test: Biology : Organismal Ecology

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

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Example Question #1 : Food Webs And Pyramids

Which of the following would be a secondary consumer?

Possible Answers:

A maple tree that stores energy harnessed from the sun in the form of sugars through a process called photosynthesis

A western diamondback rattlesnake that preys on field mice that eat seeds and berries

Earthworms, bacteria and fungi that decompose plant matter on the forest floor to replenish the soil

A black-tailed deer that browses on grasses and shrubs

People who are keen to eat bear, which eats small mammals that live off berries and seeds

Correct answer:

A western diamondback rattlesnake that preys on field mice that eat seeds and berries

Explanation:

A secondary consumer is a step above the primary consumer (herbivore) on the food chain, consisting of omnivores and carnivores. A mouse that lives off plant matter and is thus a primary consumer. When a snake eats the mouse, it is the secondary consumer in the food web.

Example Question #1 : Food Webs And Pyramids

What is the ratio of energy generated by producers to the energy absorbed by the next trophic level up, that of primary consumers?

Possible Answers:

Correct answer:

Explanation:

With every advancement in the trophic level, energy converts on a ten-to-one scale. For example, ten kilograms of grain fed to a steer produces roughly one kilogram of beef. This is true for every step up the tropic food pyramid.

Example Question #3 : Ecology

Only 10% of the energy at each level of the trophic pyramid is available energy for the following trophic level. Why is so much energy lost between each level?

Possible Answers:

Not all ingested food can be absorbed into the body

All of these

All the available food cannot be eaten

The conversion of food into biomass results in heat loss

Not everything absorbed into the body is used for growth

Correct answer:

All of these

Explanation:

These are all sources of lost energy in between levels of the trophic pyramid. In the context of herbivores and carnivores: Not all food at each level can be eaten, because some prey escape their predators or they can't be found. When a predator eats its prey, not all of that tissue is digestible, such as cellulose and lignins. Lastly, everything that the predator digests is not used for new growth, and some is lost through excretion and respiration (heat).

Example Question #1 : Understanding Food Webs And Food Chains

There are a huge number of herbivores in the world, with insects being the largest and most diverse group. Given how successful these herbivores are and how abundant their plant resources are, why haven't all plants in the world been eaten by now?

Possible Answers:

Herbivore population sizes are controlled by the climate

Herbivores are limited by their predators

Most herbivores are very small

Herbivores are not diverse enough nor do they have enough adaptations to eat all plants

Herbivores generally only eat one plant

Correct answer:

Herbivores are limited by their predators

Explanation:

Herbivores are very likely limited by the predators in their own food webs, preventing them from completely overtaking the plants that they feed on. This is called the Earth is Green hypothesis, originally proposed by Hairston, Smith, and Slodobkin.

Example Question #5 : Ecology

Detritivores employ an evolutionarily successful feeding strategy of animals, in which they feed primarily on other animals' waste. Why is this an efficient approach?

Possible Answers:

There is less competition for detritus than other resources

There are no special adaptations required to be a detritivore

Nutrient content is much richer in detritus

There is more detritus than live biomass

Dung is much easier to digest because its already been digested by another animal

Correct answer:

Dung is much easier to digest because its already been digested by another animal

Explanation:

Detritivores are successful because it is much more efficient to digest dung because it doesn't require much extra digesting, as another animal has already done it. Detritivores can generally have a much less complicated digestive system and save themselves the energetically expensive process of digesting new plants or animals. Detritivores are also important to the ecosystem because they cycle the nutrients in dung back into the food chain. There is no evidence that detritivores experience less competition, nor that detritus is in excess to live organisms.

Example Question #6 : Ecology

Plants, which are capable of primary production via photosynthesis, are the base of many global food webs. However, this is an inefficient process relative to how much total solar energy is available. What percentage of incoming solar radiation is actually converted into plant tissue and is available to the next trophic level?

Possible Answers:

Correct answer:

Explanation:

Less than half of total solar energy is within the photosynthetically active wavelength range, and plants to not absorb all of this energy due to reflection and refraction. Thus, only about 1-5% of incoming solar radiation is actually converted to plant biomass, which serves as the base for all food chains. This is why herbivorous animals generally have to eat extremely high quantities of plants to achieve adequate nutrition.

Example Question #1 : Organismal Ecology

Eusocial insects, like many species of ants, are some of the most well known and successful social animals in the world. What factors are necessary for an insect species to be eusocial?

I. Cooperative brood care between different individuals

II. Division of labor by reproductive capability

III. Overlap of generations

IV. Adults care for their own offspring for some time

Possible Answers:

III and IV

I, II, III, and IV

I, II, and III

II only

I and II

Correct answer:

I, II, and III

Explanation:

Eusociality is defined by options I, II, and III. A species must cooperate on brood care (think ants bringing food back to the colony), labor is divided by reproductive ability (think sterile worker bees and queens) and the generations must overlap so that the colony is maintained properly.

Example Question #1 : Reproductive Patterns And Principles

K-strategist species exhibit all of the following characteristics except __________.

Possible Answers:

Relatively long life expectancies

Late age of maturity

Little time spent by parents raising offspring

Produces relatively few offspring

Correct answer:

Little time spent by parents raising offspring

Explanation:

Species designated as K-strategists thrive through longevity and have a higher survival rate at birth, but produce far fewer offspring. Examples include elephants and whales. Consider an elephant; it may produce relatively few baby elephants, but these baby elephants each have the potential to live relatively long lives. On the other hand, contrast K-strategists like elephants with r-strategists like rats, locusts, and flies. These species are designated as r-strategists because in contrast, they produce numerous offspring, few of which may survive to adulthood, and each one of which reaches maturity quickly and lives a relatively short life. K-strategists in general spend more time than r-strategists caring for and raising their offspring; they have fewer offspring, so they put more care into ensuring the survival of each one. Contrast elephants with frogs to see this difference; elephants care for their young, while frogs lay their eggs and care for their offspring very little, if at all.

Example Question #1 : Population Ecology

A species designated as "r-strategist" is characterized by all of the following except __________.

Possible Answers:

Small size

Long life expectancy

Low age of maturity

High reproductive rate

Little time spent by parents caring for and raising offspring

Correct answer:

Long life expectancy

Explanation:

Species described as "r-strategist" have a survival strategy of producing large numbers of offspring, a short life expectancy, and typically smaller body sizes. Examples include mice, locusts, and frogs. These species survive by producing lots of offspring, since many individuals don't survive to adulthood.

Example Question #1 : Organismal Ecology

K-strategist populations are more commonly regulated by ____________ limiting factors, and r-strategist populations are regulated by ___________ limiting factors.

Possible Answers:

none of these

density-independent, density-independent

density-dependent, density-dependent

density-independent, density-dependent

density-dependent, density-independent

Correct answer:

density-dependent, density-independent

Explanation:

K-strategist populations are more commonly regulated by density-dependent limiting factors. Their population sizes hover around a carrying capacity that is dependent on factors that increase in severity with the density of the population. On the other hand, r-strategist populations are regulated by density-independent limiting factors. They reproduce rapidly until a density-independent factor causes many of them to die.

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