50. Population Ecology

To calculate the human population density of your community, you would need to know the number of people living there and __________.

Which of the following choices is an expression of a population density?

When needed resources are unevenly distributed, organisms often show a(n) __________ dispersion pattern.

Organisms that live in a homogenous abiotic environment and cooperate to avoid being eaten would likely show a(n) __________ pattern of dispersion.

Herring gulls fiercely defend the areas around their nests in cliff-top breeding colonies. Within the colony they would show a __________ dispersion pattern.

Pine trees in a forest tend to shade and kill pine seedlings that sprout nearby. This causes the pine trees to __________.

What may a demographer study?

Life tables typically follow the fate of a cohort, a __________.

An oak tree produces thousands of acorns, but very few grow into mature oak trees. The oak tree exhibits a __________ survivorship curve.

Chimpanzees have a relatively low birth rate. They care for their young, and most chimps live a long life. The chimp survivorship curve would look like __________.

Which of the following describes the distribution of survivorship or mortality for a population that has a Type II survivorship curve?

Kingfish, Louisiana, had a population of 1,100 individuals. They had a birth rate of 12/100, a death rate of 8/100, and an emigration (individuals leaving the population) rate of 2/100. How many people were added to Kingfish's population in one year?

To calculate the __________ of a nation, researchers summarize arable land, pasture, fossil energy land, and several other factors appropriated by each nation to produce all of the resources it consumes and to absorb all the waste it generates.

What absolutely essential resource is likely to limit the carrying capacity of Earth for humans?

An ecologist would suspect a population to be growing rapidly if it __________.

If you wanted to determine what percentage of the population of Thailand is less than 10 years old, you could look at __________.

The cyclic growth exhibited by populations of snowshoe hares in the North American taiga most likely results from __________.

Which of the following is most likely a density-dependent growth regulator of animal populations?

A particular environmental change causes the deaths of 25 individuals in a herd of 100 wild horses, and it kills 50 individuals in a herd of 200 horses. In this case, the growth of a wild horse population is most likely limited by __________. (Assume that the two herds are found in territories of equal size.)

A certain species of seal breeds and rears its young on rocky beaches. Competition for breeding sites is fierce, and males that do not secure a site will not reproduce. This behavior is an example of which mechanism of density-dependent population regulation?

Which of the following would most likely be an example of a density-independent factor limiting population growth?

Although there are organisms whose life histories fall somewhere between iteroparity and semelparity, life history always represents a trade-off. Why is this?

A dog gives birth to three puppies one year. Three years later, she gives birth to six puppies. Which type of life history pattern is characteristic of this organism?

What are three basic issues that life histories entail?

When the per capita birth rate equals the per capita death rate, __________.

A population will always grow exponentially under what circumstances?

Which of the following populations probably exhibits exponential growth?

No population can grow indefinitely. The ultimate size of any population is limited by __________.

A variety of opossum that lives on an island with no predators lives much longer than its relatives on the mainland, even when both are kept safely in a zoo. The island variant's genes have been selected for slow aging, whereas the mainland variant's genes have been selected for quick reproduction. The island opossum exhibits __________ selection, and the mainland opossum exhibits __________ selection.

The logistic growth model differs from the exponential growth model in that it __________.

A newly mated queen ant founds a nest in an unoccupied patch of suitable habitat. Assuming that no disasters strike the nest, which of the following types of equation is likely to best describe the population growth of the new colony?

In an equilibrium population (at its carrying capacity), thousands of eggs and hundreds of tadpoles are produced by a single pair of frogs. On average, about how many offspring per pair will live to reproduce?

A population that is growing logistically __________.

A wildlife biologist is trying to predict what will happen to a bear population if bear hunting is banned. He had the equations all worked out but then realized that he had grossly underestimated the amount of food available to the bears. To make his prediction more accurate he should __________ the value of __________ in his equation. (Consider food to be a factor that limits the size of the bear population.)

A population that grows rapidly at first and then levels off at carrying capacity can be modeled __________.

Assuming that r has a positive value, in the formula dN/dt = r_maxN(K – N)/K, the factor rN tends to cause the population to do what?

Population ecologists follow the fate of same-age cohorts to a. determine a population's carrying capacity. b. determine the birth rate and death rate of each group in a population. c. determine if a population is regulated by density-dependent processes. d. determine the factors that affect the size of a population.

Use this graph of the idealized exponential and logistic growth curves to complete the following. a. Label the axes and curves on the graph. b. Give the formula that describes the blue curve. c. What does the dotted line represent? d. For each curve, indicate and explain where population growth is the most rapid. e. Which of these curves best represents global human population growth?

What is usually true of exponential growth? Select True or False for each statement. T/F The population is growing. T/F The per capita growth rate is constant. T/F The per capita growth rate increases rapidly over time. T/F The per capita growth rate is very high.

Add labels to the figure that follows, which illustrates the predicted pattern of changes in human population growth rates when death rates fall.

A population's carrying capacity a. may change as environmental conditions change. b. can be accurately calculated using the logistic growth model. c. increases as the per capita population growth rate decreases. d. can never be exceeded.

The graph below shows the demographic transition for a hypothetical country. Many developed countries that have achieved a stable population size have undergone a transition similar to this. Answer the following questions concerning this graph. a. What does the blue line represent? The red line? b. This diagram has been divided into four sections. Describe what is happening in each section. c. In which section(s) is the population size stable? d. In which section is the population growth rate the highest?

In what populations does exponential growth tend to occur? a. populations that colonize new habitats b. populations that experience intense competition c. populations that experience high rates of predation d. populations that have surpassed their carrying capacity

Explain why a decrease in population growth rate is expected as a nonhuman population approaches carrying capacity.

Scientific study of the population cycles of the snowshoe hare and its predator, the lynx has revealed that a. predation is the dominant factor affecting prey population cycling. b. hares and lynx are so mutually dependent that each species cannot survive without the other. c. both hare and lynx population sizes are affected mainly by abiotic factors. d. the hare population is r-selected and the lynx population is K-selected.

After seeds have sprouted, gardeners often pull up some of the seedlings so that only a few grow to maturity. How does this practice help produce the best yield? a. by increasing K b. by decreasing r c. by reducing intraspecific competition d. by adding a density-independent factor to the environment

If most individuals in a population are young, why is the population likely to grow rapidly in the future? a. Death rates will be low. b. The population has a skewed age distribution. c. Immigration and emigration can be ignored. d. Many individuals will begin to reproduce soon.

When individuals in a population are evenly spaced throughout their habitat, their dispersion is termed as                   . a. clumped; b. uniform; c. random; d. excessive; e. exponential

A population growing exponentially                   . a. is stable in size; b. adds a fixed number of individuals every generation; c. adds a larger number of individuals in each successive generation; d. will likely expand forever; e. will not crash

Analyzing ecological footprints reveals that a. Earth's carrying capacity would increase if per capita meat consumption increased. b. current demand by industrialized countries for resources is much smaller than the ecological footprint of those countries. c. it is not possible for technological improvements to increase Earth's carrying capacity for humans. d. the ecological footprint of the United States is large because per capita resource use is high.

To figure out the human population density of your community, you would need to know the number of people living there and a. the land area in which they live. b. the birth rate of the population. c. the dispersion pattern of the population. d. the carrying capacity.

Why is there a trade-off between survivorship and fecundity?

Based on current growth rates, Earth's human population in 2019 will be closest to a. 2.5 million. b. 4.5 billion. c. 7.5 billion. d. 10.5 billion.

The term (K−N)/K a. is the carrying capacity for a population. b. is greatest when K is very large. c. is zero when population size equals carrying capacity. d. increases in value as N approaches K.

Which of the following species is most likely to have a Type III survivorship curve? a. humans, Homo sapiens b. common lizards, Zootoca vivipara c. thale cress plants, Arabidopsis thaliana d. lynx cats, Lynx canadensis

According to the graph shown here, the carrying capacity for fruit flies in the environment of the culture bottle is                   . a. 0 flies; b. 100 flies; c. 150 flies; d. between 100 and 150 flies; e. impossible to determine

The observation that members of a population are uniformly distributed suggests that a. resources are distributed unevenly. b. the members of the population are competing for access to a resource. c.the members of the population are neither attracted to nor repelled by one another. d. the density of the population is low.

With regard to its rate of growth, a population that is growing logistically a. grows fastest when density is lowest. b. has a high intrinsic rate of increase. c. grows fastest at an intermediate population density. d. grows fastest as it approaches carrying capacity.

Pose a hypothesis to explain why the human population has undergone especially rapid growth over the past 200 years. Describe two examples of density-dependent factors that limit human population growth. Is it possible that humans have surpassed Earth's carrying capacity?

All of the following are density-dependent factors that can influence population size except                   . a. weather; b. food supply; c. waste concentration in the environment; d. infectious disease; e. supply of suitable habitat for survival

In contrast to nonhuman populations, human population growth rates have begun to decline due to                   . a. voluntarily increasing death rates; b. voluntarily decreasing birth rates; c. involuntary increases in death rates; d. involuntary decreases in birth rates; e. density-dependent factors

According to the logistic growth equation dNdt=rN(K−N)K a. the number of individuals added per unit time is greatest when N is close to zero. b. the per capita population growth rate increases as N approaches K. c. population growth is zero when N equals K. d. the population grows exponentially when K is small.

Which of the following represents a demographic transition? a. A population switches from exponential to logistic growth. b. A population reaches a fertility rate of zero. c. There are equal numbers of individuals in all age-groups. d. A population switches from high birth and death rates to low birth and death rates.

Explain why biologists want to maintain (a) 'habitat corridors' that connect populations in a metapopulation, and (b) unoccupied habitat that is appropriate for the species in question.

Populations that rely on stored resources are likely to overshoot the carrying capacity of the environment and consequently experience a(n)                   . a. demographic momentum; b. cultural carrying capacity; c. decrease in death rates; d. population crash; e. exponential growth

During exponential growth, a population always a. has a constant per capita population growth rate. b. quickly reaches its carrying capacity. c. cycles through time. d. loses some individuals to emigration.

Skyrocketing growth of the human population appears to be mainly a result of a. a drop in death rate due to sanitation and health care. b. better nutrition boosting the birth rate. c. the concentration of humans in cities. d. social changes that make it desirable to have more children.

Indicate what is correct and incorrect about this statement: If lizards want to survive during climate change, they can evolve new life-history traits.

The current carrying capacity of Earth for the human population may have been inflated by                   . a. demographic momentum; b. the tendency for women to want to control family size; c. an artificially low number of density-independent factors; d. our use of fossil fuels; e. recent population crashes

Which of the following statements about human populations in industrialized countries is correct? (A)Birth rates and death rates are high. (B)Average family size is relatively large. (C)The population has undergone the demographic transition. (D)The survivorship curve is Type II.

Which of the following statements about human populations in industrialized countries is incorrect? a. Birth rates and death rates are high. b. Average family size is relatively small. c. The population has undergone the demographic transition. d. The survivorship curve is Type I.

According to data on ecological footprints, a. the carrying capacity of the world is 10 billion. b. Earth's resources are sufficient to sustain future generations at current levels of consumption. c. the ecological footprint of individuals in the United States is more than twice the world average. d. nations with the largest ecological footprints have the fastest population growth rates.

When wild plant and animal populations are logged, fished, or hunted, only the oldest or largest individuals tend to be taken. Many of the commercially important species are long lived and are slow to begin reproducing. If harvesting is not regulated carefully and exploitation is intense, what impact does harvesting have on a population's age structure? How might harvesting affect the population's life table and growth rate?

Demographic momentum refers to the tendency for                   . a. low population growth rates to continue to decline; b. high population growth rates to continue to increase; c. populations to continue to grow in number even when growth rates reach zero; d. populations to continue to grow in number even when women are reducing the number of children they bear; e. women to continue to have children even though they no longer wish to

What are some factors that might have a density-dependent limiting effect on population growth?

Make a rough sketch of the age distribution in a developing versus a developed country, and explain why the shapes of the diagrams are different. How is AIDS, which is a sexually transmitted disease, likely affecting the age distribution in countries hard hit by the epidemic?

What is survivorship? What does a survivorship curve show? Explain what the three survivorship curves tell us about humans, squirrels, and clams.

Burmese pythons (Python molurus bivittatus) are constricting snakes that can reach enormous sizes (up to 7 meters in length). They are native to Southeast Asia but were released into southern Florida from the pet trade. Many other snakes occur naturally in this area. Are the introduced pythons a problem? Burmese pythons were first found in the wetlands of Everglades National Park in the 1980s, but only rarely. The accompanying graph shows what happened next. Most of the data are derived from chance encounters of pythons on roads (pythons are notoriously difficult to find). How would you describe the type of population growth in pythons from 2000 to 2008? a. logistic b. exponential c. linear d. logarithmic

Describe the factors that might produce the following three types of dispersion patterns in populations.

Burmese pythons (Python molurus bivittatus) are constricting snakes that can reach enormous sizes (up to 7 meters in length). They are native to Southeast Asia but were released into southern Florida from the pet trade. Many other snakes occur naturally in this area. Are the introduced pythons a problem? Researchers hypothesize that the severe winter of 2010 caused the decline in the number of pythons encountered that year. Is cold weather typically a density-dependent factor or a density-independent factor? Explain the difference.

The mountain gorilla, spotted owl, giant panda, snow leopard, and grizzly bear are all endangered by human encroachment on their environments. Another thing these animals have in common is their K-selected life history traits. Why might they be more easily endangered than animals with r-selected life history traits? What general type of survivorship curve would you expect these species to exhibit? Explain your answer.

Burmese pythons (Python molurus bivittatus) are constricting snakes that can reach enormous sizes (up to 7 meters in length). They are native to Southeast Asia but were released into southern Florida from the pet trade. Many other snakes occur naturally in this area. Are the introduced pythons a problem? The data in the graph show the number of pythons that were encountered, not the total number of pythons in the population. Design a mark–recapture experiment to estimate the total population size of pythons, and list at least two assumptions you would be making in your experiment.

SCIENTIFIC THINKING Another hypothesis for snowshoe hare population cycles proposes that they are caused by sunspot activity. According to this hypothesis, sunspot activity affects the chemicals present in the plants eaten by hares, which in turn affects the quality of the food. What testable predictions are generated by this hypothesis?

Burmese pythons (Python molurus bivittatus) are constricting snakes that can reach enormous sizes (up to 7 meters in length). They are native to Southeast Asia but were released into southern Florida from the pet trade. Many other snakes occur naturally in this area. Are the introduced pythons a problem? A life table would help researchers make predictions about python population growth. If you were to track a cohort of pythons over time to construct a detailed life table, what kind of data would you want to collect?

Many people regard the rapid population growth of developing countries as our most serious environmental problem. Others think that the growth of developed countries, though slower, is actually a greater threat to the environment. What kinds of environmental problems result from population growth in (a) developing countries and (b) developed countries? Which do you think is the greater threat? Why?

Burmese pythons (Python molurus bivittatus) are constricting snakes that can reach enormous sizes (up to 7 meters in length). They are native to Southeast Asia but were released into southern Florida from the pet trade. Many other snakes occur naturally in this area. Are the introduced pythons a problem? Pythons are generalist predators, consuming a wide variety of prey including birds, mammals ranging from rodents to deer, and alligators. A road survey showed a 99 percent decrease in the frequency of raccoon and opossum observations within python areas from 2003 to 2011. Rabbits and foxes have also disappeared from the area. Do you think food availability limits, or could limit, the carrying capacity of Burmese pythons in the Everglades?

Burmese pythons (Python molurus bivittatus) are constricting snakes that can reach enormous sizes (up to 7 meters in length). They are native to Southeast Asia but were released into southern Florida from the pet trade. Many other snakes occur naturally in this area. Are the introduced pythons a problem? The range of Burmese pythons in Florida is expanding rapidly. List at least one abiotic factor and one biotic factor that might limit the range of pythons.