# Critical Thinking Questions

53.
Describe how a researcher could determine the population size and density of a bird population on one of the Hawaiian islands.
1. Population size can be determined by life tables. The area of the island in square kilometers is divided by the population size to determine the density of the bird population.
2. Population size can be determined by the mark and recapture method. The population size is divided by the area of the island in square kilometers to determine the density of the bird population.
3. Population size can be determined by life tables. The population size is divided by the area of the island in square kilometers to determine the density of the bird population.
4. Population size can be determined by the mark and recapture method. The area of the island in square kilometers is divided by the population size to determine the density of the bird population.
54.
Give examples of how two different populations of organisms might have the same population density, but different dispersal patterns.
1. Two populations could occupy the same range with the same number of individuals, giving different dispersal patterns. However, both the populations may be dispersed randomly throughout the range, giving identical population densities.
2. Two populations could occupy the different range with the different number of individuals, giving different dispersal patterns. However, both the populations may move over this range in a herd, giving identical population densities.
3. Two populations could occupy the same range with the different number of individuals, giving identical population densities. However, one population may move over this range in a herd while the other population may be dispersed randomly throughout the range.
4. Two populations could occupy the same range with the same number of individuals, giving identical population densities. However, one population may move over this range in a herd while the other population may be dispersed randomly throughout the range.
55.
A population is observed to have very large numbers of very young individuals, but very low numbers of sexually mature individuals. What hypothesis might a researcher propose about mortality patterns in this population, and how would that researcher follow up to test her hypothesis?
1. The researcher might propose that the mortality rate of this species is very high during the developmental period after sexual maturity is reached. She can test this hypothesis by constructing a life table and calculating mortality rates at different age intervals.
2. The researcher might propose that the mortality rate of this species is very high during the developmental period before sexual maturity is reached. She can test this hypothesis by using the mark and recapture method and calculating population densities.
3. The researcher might propose that the mortality rate of this species is very high during the developmental period before sexual maturity is reached. She can test this hypothesis by constructing a life table and calculating mortality rates at different age intervals.
4. The researcher might propose that the mortality rate of this species is very low during the developmental period before sexual maturity is reached. She can test this hypothesis by constructing a quadrat and calculating mortality rates at different age intervals.
56.
An organism, such as an elephant, that invests in long-term care of its offspring faces risks to its survival as a result of this investment. Explain those risks.
1. Organisms that invest in long-term parental care have many offspring. Having many offspring means there is greater risk of rapid increase in population.
2. Organisms that invest in long-term parental care have few offspring. Having a limited number of offspring means there is greater risk to the survival of the species when a single offspring dies.
3. Organisms that invest in long-term parental care have many offspring. Having many offspring means there is greater risk to the survival of the species when a single offspring dies.
4. Organisms that invest in long-term parental care have few offspring. Having a limited number of offspring means there is greater risk of rapid increase in population.
57.
A honey bee colony contains one queen, hundreds of drones, and many thousands of worker bees. The queen produces eggs, the drones produce sperm, and the workers are sterile. Explain how the reproductive strategy of honey bees benefits the survival of the species. (credit: Food and Agriculture Organization of the United Nations)
1. The fertile queen and drones produce many offspring while sterile worker bees do not benefit the survival of the species.
2. Worker bees produce many offspring while the sterile queen and drones do not benefit the survival of the species.
3. The sterile queen and drones use the energy taken in by them for their own growth, growth and maintenance of the hive, and protection and nurturing of offspring.
4. Sterile worker bees use the energy taken in by them for their own growth, growth and maintenance of the hive, and protection and nurturing of offspring.
58.
Two different plant species expend approximately the same amount of energy on reproduction, yet one produces many seeds in a season and the other produces very few. Explain what is likely to be true of the seeds of these two species.
1. In the plant species that produces many seeds, most of the energy is used to produce seeds, of which only a few will germinate and produce another plant. In the species that produces few seeds, most of the energy is used to increase the chances of seeds produced to germinate and grow into an adult plant.
2. In a plant species that produces many seeds, most of the energy is used to produce seeds, most of which will germinate and produce another plant. In a species that produces few seeds, most of the energy is used to increase the chances of seeds produced to germinate and grow into an adult plant.
3. In a plant species that produces many seeds, most of the energy is used to produce seeds, of which only a few will germinate and produce another plant. In a species that produces few seeds, most of the energy is used to reduce the chances of seeds produced to germinate and grow into an adult plant.
4. In a plant species that produces many seeds, most of the energy is used to increase the chances of seeds produced to germinate and grow into an adult plant. In a species that produces few seeds, most of the energy is used to produce those seeds, which will germinate and produce another plant.
59.
Explain how rmax would be expected to differ for an elephant and a flea, and how that changes the time scale over which populations of these two animals would be studied.
1. The rmax would be greater for an elephant because elephants reproduce at a faster rate than fleas. A shorter time scale would be used to study changes over several elephant generations.
2. The rmax would be greater for a flea because fleas reproduce at a faster rate than elephants. A shorter time scale would be used to study changes over several flea generations than over several elephant generations.
3. The rmax would be greater for a flea because fleas reproduce at a faster rate than elephants. A longer time scale would be used to study changes over several flea generations than over several elephant generations.
4. The rmax would be greater for an elephant because elephants grow at an exponential rate, so the population growth rate is greatly increased. A shorter time scale would be used to study changes over several elephant generations.
60.

These data were collected on a population of beetles in Florida.

Based on the data, how would you describe population growth in this case and what do you predict about growth of this population in the future? Explain your reasoning.

1. Population shows logistic growth, as number of individuals approximately doubles every month and will likely continue to grow logistically until its resources become depleted. At that point, the population growth rate will slow down and level off to zero.
2. The population shows exponential growth, as the number of individuals approximately doubles every month and will likely grow logistically in the future until its resources become limited. At that point, the population growth rate will slow down and level off to zero.
3. The population shows exponential growth, as number of individuals approximately doubles every month and will likely continue to grow exponentially until its resources become limited. At that point, the growth will become logistic; the population growth rate will slow down and level off to zero.
4. The population shows logistic growth and is likely to grow exponentially as the resources are probably increasing. The population growth rate will increase in the future as well.
61.
Explain how climate change might lead to a decrease in one population’s carrying capacity and an increase in the carrying capacity of a different population.
1. Plant species that are drought-resistant would decline in warm temperatures whereas other species would thrive in number in such a climate.
2. Plant species that are pest-resistant would thrive in warm temperatures whereas other species would decline in number in such a climate.
3. Plant species that are drought-resistant would decline in cold temperatures whereas other species would thrive in number in such a climate.
4. Plant species that are drought-resistant would thrive in warm temperatures whereas other species would decline in number in such a climate.
62.
How would you compare and contrast density-dependent growth regulation with density-independent growth regulation? Give an example of each as they might affect a caterpillar population.
1. Both are environmental conditions that result in changes in population numbers. Density-independent factors have different effects on population densities whereas density-dependent factors all have the same effect at different densities. An example of the former is a caterpillar population being kept low by a pesticide because it kills them regardless of their numbers. An example of the latter is a large caterpillar population leading to a decrease in food availability, causing the caterpillar population to decline.
2. Both are environmental conditions that result in changes in population numbers. Density-independent factors have the same effect at all population densities whereas density-dependent factors have different effects at different densities. An example of the former is a caterpillar population being kept low by a pesticide because it kills them regardless of their numbers. An example of the latter is a large caterpillar population leading to a decrease in food availability, causing the caterpillar population to decline.
3. Both are environmental conditions that result in changes in population numbers. Density-independent factors have the same effect at all population densities whereas density-dependent factors have different effects at different densities. An example of the former is of a caterpillar population being kept low by a pesticide because it kills them only when their numbers are low. In the case of the latter, a large caterpillar population leads to a decrease in food availability, which will cause the caterpillar population to decline.
63.
Why doesn’t a frog, which is an r-selected species, care for its offspring in the way a wolf, which is a K-selected species, cares for its offspring?
1. Frogs have been selected by stable, predictable environments, therefore they do not feel the need to care for their offspring like wolves.
2. Frogs use very little energy to produce large numbers of offspring, therefore they do not have enough remaining to nurture them.
3. Smaller animals like frogs do not care for their offspring, whereas larger animals like wolves do.
4. Frogs expend a lot of energy to produce large numbers of offspring, leaving less energy for nurturing them.
64.
Explain which features of a logistic growth curve are the same for every population exhibiting logistic growth and which features might vary from one population to another.
1. The overall S-shape would be the same for all populations. The actual x-y values on the graphs, population numbers corresponding to starting populations, and the ending carrying capacities could differ.
2. The overall carrying capacities would be the same for all populations. The actual x-y values on the graph and population numbers corresponding to the starting populations could differ.
3. The overall S-shape would be the same for all populations showing logistic growth. The only factor that could differ is the actual x-y values on the graphs indicating the time frames for the growth curves.
4. The x-y values on the graphs indicating the time frames for the growth curves would be the same. Overall S shape and population numbers corresponding to the starting populations could differ.
65.
Explain why the concept of carrying capacity is important when discussing human population growth.
1. Humans can decrease the carrying capacity of their environment by developing food production methods and engineering high quality shelters, which enables more people to live than would otherwise be possible.
2. Humans have been able to change the carrying capacity of their environment, which enables more people to survive. By decreasing their own carrying capacity, humans are responsible for their population boom.
3. Humans have been able to change the carrying capacity of their environment, which enables more people to live. By increasing their own carrying capacity, humans are responsible for their population boom.
4. Humans can increase the carrying capacity of their environment by developing food production methods and engineering high quality shelters, which enables fewer people to live than would otherwise be possible. This would result in population collapse.
66.
The Industrial Revolution began with the invention of the steam engine. At about the same time, human population began increasing exponentially. Explain how these two events are linked to the idea that humans are able to change the carrying capacity of their environment.
1. The invention of the steam engine enabled people to use machines to carry out farming activities. The amount of available resources needed to sustain human life increased with the invention of machines. This increase in resources spurred exponential population growth.
2. The invention of the steam engine enabled people to develop pest-resistant crop varieties. The amount of available resources needed to sustain human life increased with the invention of machines. This increase in resources spurred exponential population growth.
3. The amount of available resources needed to sustain human life decreased with the invention of machines, but the carrying capacity increased. This increase in carrying capacity spurred exponential population growth.
4. The invention of the steam engine enables the environment to be changed according to the needs of the people. This regulation of environmental conditions spurred exponential population growth.
67.

This diagram shows the age structure for a country. Analyze the age structure.

(credit: Quia)

1. This country is likely to be an economically developing country because it has a fairly even distribution of individuals in all age groups.
2. This country is likely to be an economically developed country because it has many more very young people and very few old people.
3. This country is likely to be an economically developed country because it has a fairly even distribution of individuals in all age groups.
4. This country is likely to be an economically undeveloped country because it has many more very young people and very few old people.
68.

The global ecological footprint is defined as the total land area needed to supply all of the resources consumed by all humans. This graph shows the relationship between time and the global human footprint measured in number of planet Earths. Analyze the graph.

(credit: EPA Victoria)

What has been the consequence of human population change so far, and what are the consequences of continued population change in the future?

1. The human population has exceeded Earth’s water resources. If the human population keeps increasing, the ecological footprint of humans will increase far beyond the ability of Earth to support human population and our population could crash.
2. The human population has exceeded Earth’s land area. If the human population keeps increasing, the ecological footprint of humans will increase far beyond the ability of Earth to support human population and our population could crash.
3. The human population has exceeded Earth’s land area to supply our resources of many types. If the human population keeps increasing, the birth and death rates will decrease and our population could crash.
4. The human population has exceeded Earth’s water resources. If the human population keeps increasing, the birth and death rates will decrease and our population could crash.
69.

This graph shows a predator-prey cycle for wolves and moose.

Explain why the graphs do not resemble the idealized graphs used as models of the predator-prey cycle.

1. This graph reflects all of the influences on both populations in addition to the predator-prey influences.
2. This graph reflects all of the influences on both populations, but not the predator-prey influences.
3. This graph reflects just the influence of predator-prey interactions on both populations.
4. This graph reflects some of the influences on both populations other than the predator-prey influences.
70.
Suppose a population of lizards becomes divided into two groups on two different islands after a devastating tsunami. No predators of the lizard are present on one island, and on the other island is a fierce predator that uses the lizard as its primary source of food. Assuming both populations encounter similar environments in every other way, and both survive and grow over the next 100 years, how do you predict any of the characteristics of the two lizard populations to differ at the end of that time? Give specific examples to explain your prediction.
1. The lizards on the island with no predators will likely evolve adaptations such as camouflaged coloration, sharp spines, or toxins to defend against this predator. These adaptations will likely be absent in the other population because they are adapted to other predators.
2. The lizards that survive the fierce predator will likely evolve adaptations such as camouflaged coloration, sharp spines, or toxins to defend against this predator. These adaptations will likely be absent in the other population because they are adapted to other predators.
3. The lizards that survive the fierce predator will likely evolve adaptations such as camouflaged coloration, sharp spines, or toxins to defend against this predator. These adaptations will likely be absent in the other population because this predator is not a factor in their survival.
4. The lizards on the island with no predators will likely evolve adaptations such as camouflaged coloration, sharp spines, or toxins to defend against this predator. These adaptations will likely be absent in the other population because they have survived this predator.
71.
The downy woodpecker and the hairy woodpecker are two species that live in the same habitats. The downy woodpecker is slightly smaller and has a smaller beak than the hairy woodpecker. The downy woodpecker uses its bill to search for food on small twigs and branches while the hairy woodpecker is most often observed searching for food on tree trunks. Explain how the competitive exclusion principle relates to this example.
1. Both woodpeckers have identical bill structure, but do not access their food from the same places in the habitat. They do not directly compete with one another for food and thus, can coexist in the same habitat.
2. Both live in the same habitat and have some similarities, but access their food from the same places in the habitat. In this way, the two species can coexist in the same habitat.
3. Both woodpeckers share similarities in their bill structures. So, they directly compete with one another for food. This directly relates to the competitive exclusion principle.
4. Both live in the same habitat and have some similarities, but do not access their food from the same places in the habitat. In this way, the two species can coexist in the same habitat.
72.
Honey bees are pollinators. Identify the type of symbiotic relationship that exists between honey bees and flowering plants, and explain why your reasoning.
1. This is commensalism because bees help plants pollinate and, in turn, obtain nectar from the plants.
2. This is a mutualistic relationship, because bees obtain nectar from the plants, but do not provide any benefits to the plants.
3. This is commensalism, because bees obtain nectar from the plants, but do not provide any benefits to the plants.
4. This is a mutualistic relationship, because bees help plants pollinate and, in turn, obtain nectar from the plants.
73.
Prairie dogs are considered a keystone species in the western U.S. because of their extensive burrowing activities and their role as a prey animal. Explain why these characteristics would result in the keystone role of prairie dogs in their ecosystem.
1. Prairie dogs provide protection and shelter for small animals and harm predator animals in the ecosystem.
2. Without the prairie dogs, the ecosystem might collapse due to lack of protection and shelter for small animals and lack of prey to sustain large predator animals.
3. Prairie dogs dig underground burrows, reducing aeration in the soil and preventing excessive growth of plants above ground.
4. The burrows prairie dogs dig underground provide shelter for other species of animals as well as protection from predators, but prevent growth of plants above ground.
74.

Mating pairs of two different species of parrots sometimes lay their eggs in the same nest. When this happens, only one mating pair ends up parenting the chicks even though chicks of both species may be present. The chicks in such mixed nesting groups displayed some interesting behaviors summarized in the table below. Classify these behaviors as innate or learned, and explain how they compare.

1. An alarm call is an innate behavior and a contact call is a learned behavior. Innate behavior comes out automatically in response to a stimulus whereas learned behavior develops over time after observing other birds carrying out the behavior.
2. The alarm call is a learned behavior and contact call is an innate behavior. Learned behavior develops over time after observing birds carrying out the behavior whereas innate behavior comes out automatically in response to a certain stimulus.
3. The alarm call is an innate behavior and contact call is a learned behavior. Innate behavior develops over time in response to stimulus after continuous exposure. Learned behavior develops over time after observing other birds carrying out their behavior.
4. The alarm call is a learned behavior and contact call is an innate behavior. Learned behavior comes out automatically whereas innate behavior develops over time in response to stimulus after continuous exposure.
75.
Mammals such as humans show a behavior known as the flight or fight response. Explain how natural selection was likely involved in the development of this behavior that can be observed in humans today.
1. Individuals showing fight or flight behavior was more likely to survive than individuals lacking the trait. This trait got randomly selected by natural selection, thus became preferentially incorporated into the human lineage.
2. Individuals showing fight or flight behavior were more likely to survive than individuals lacking the trait. Sudden, inheritable changes were naturally selected, which included the fight or flight behavior. Thus, this response was incorporated into the human lineage.
3. Individuals showing fight or flight behavior were more likely to survive than individuals lacking this trait. Therefore surviving individuals passed on their trait to offspring while non-surviving individuals do not. Thus, this response became incorporated into human lineage.
4. Individuals showing fight or flight behavior were not more fit than individuals lacking this trait. However, the trait was selected by natural selection due to a random chance event in the gene frequency of individuals showing fight or flight behavior.
76.
A researcher studying minnows, a type of fish, kept two groups of 20 fish in separate containers. The containers were linked by a pair of small tubes outfitted with a pump that constantly circulated water between both tanks. The researcher observed both groups of fish after placing a larger fish known to be a predator of minnows into one of the tanks. Fish in both tanks demonstrated alarm behavior. How can you explain these observations?
1. Fish in the tank that received the predator released alarm signals in chemical form. These compounds circulated and reached the other tank, eliciting an alarm response from the fish there nonetheless.
2. Fish in the tank that received the predator released alarm signals in the form of electrical signals. These compounds circulated and reached the other tank, eliciting an alarm response from the fish there nonetheless.
3. The predator introduced in one tank of fish released alarm signals in chemical form. These compounds circulated and reached the other tank, eliciting an alarm response from the fish there nonetheless.
4. Fish in the tank that did not receive the predator released alarm signals in the chemical form. These compounds circulated and reached the other tank and elicited an alarm response from the fish.
77.
In some species, males expend a great deal of energy in courtship rituals, whereas males of other species expend much less energy, using other ways of attracting mates such as producing colorful plumage. What does this mean for any leftover energy that leftover males of these species might have to devote to care for offspring?
1. Males of species carrying out courtship rituals are more likely to assist with parental care, whereas males that use colorful plumage to attract mates are less likely to assist with parental care.
2. Males of species carrying out courtship rituals are more likely to assist with parental care, whereas males that use colorful plumage to attract mates are more likely to assist with parental care because they have more energy available.
3. Males of species carrying out courtship rituals and males of species that use colorful plumage to attract mates are both likely to assist with parental care.
4. Males of species carrying out courtship rituals and males of species that use colorful plumage to attract mates are both unlikely to assist in parental care because the females would be involved.
78.
Female spotted sandpipers fight each other for resource-rich territories on their beach breeding grounds. Based on this, which mating type would most likely be operating in this species?
1. Polyandrous mating is most likely operating as the females are establishing territories apart from other females. The females will then attract males to the resources they control which will result in many males attracted to few females with the richest territories.
2. Polygynous mating is most likely operating as the females are establishing territories apart from other females. The females from all territories would attract males to the resources they control, which would result in few males attracted to many females in each territory.
3. Polyandrous mating is most likely operating as the females are establishing territories apart from other females. The females from all territories would attract males to the resources they control, which would result in few males attracted to many females in each territory.
4. Polygynous mating is most likely operating as the females are establishing territories apart from other females. The females will then attract males to the resources they control which would result in many males attracted to few females with the richest territories.
79.
Describe Pavlov’s dog experiments as an example of classical conditioning.
1. Pavlov demonstrated classical conditioning through a maze running experiment with the dog. The motivation for the dog to work its way through the maze was a piece of food at the end of the maze. The dog ran in one trial per day and had food available at the end of the run.
2. Pavlov hung a chicken piece in a cage too high for the dog to reach and several boxes were placed randomly on the floor. Eventually the dog was able to stack the boxes and climb on top to get the chicken piece through classical conditioning.
3. Pavlov put a dog in a large box that contained a lever that would dispense food to the dog when pressed. While initially the dog would push the lever a few times by accident, it eventually associated pushing the lever with getting the food through classical conditioning.
4. Pavlov sounded a bell whenever food was presented to a dog, which produced saliva in response to the sight or smell of the food. Through classical conditioning, the dog started responding to the bell ringing with salivation as the dog came to associate the bell sound with the arrival of food.