Ch. 11: population distributions

You are performing an experiment to compare the ability of five fish species to distribute themselves in an ideal free distribution under laboratory conditions. Each species consumes the same food and eats the same amount per day. You test each species in separate but identical aquaria. Each day you add 1 mg of water fleas, a preferred fish prey item, to side A of the aquaria and 7 mg of water fleas to side B. Although you were unable to collect the same number of fish individuals from each species, you record the number of individuals of each species that distribute themselves on each side of their respective aquaria. You draw up the following table showing your results: Which fish species most closely exhibits an ideal free distribution under the laboratory conditions of your experiment?

B; see pic

In a population that occupies multiple habitat patches, why shouldn't all individuals try to move to and live only in the habitat patch that has the highest-quality resources?

Per capita resource availability would be very low.

True or false? If two forests are separated by an open field, a stream that has a narrow band of trees along its banks could serve as a habitat corridor between the two forests.

True

True or false? The geographic range of the emerald ash borer has expanded rapidly in the United States, largely from unintentional human assistance

True

True or false? The ideal free distribution tells us that the persistence of populations living in low-quality habitats is dependent upon the dispersal of offspring from populations living in high-quality habitats.

True

A species' _____ is the range of abiotic and biotic conditions under which it lives.

realized niche

You are performing a mark-recapture survey of sea turtles that breed on a beach on the east coast of Brazil once every year. In the initial sample, you capture 134 sea turtles and mark their shells. The next year, you return to the same beach and capture 157 sea turtles. Of those individuals, you find that 87 have markers from the previous year's survey. What do you estimate is the approximate size of the sea turtle population that reproduces on this beach?

242

A nonmigratory male bird hatches in a nest in New Hampshire. Once the bird fledges, he begins flying west little by little to look for a good territory to attract a mate. In its first year, the bird travels 10.3 km. In his second year, the bird travels 12.4 km. In his third year, the bird travels 6.4 km until summer, when he finds a female and mates. He does not travel any more in the third year. In the spring of the fourth year, after his young have fledged, the male sets off westward again and travels 9.7 km before a falcon eats him. What was the lifetime dispersal distance of the bird?

29.1 km

Using mark-recapture techniques, you have estimated that there are 421 total grizzly bears on Kodiak Island, Alaska. During your initial sampling, you captured and marked 121 grizzlies, of which you recaptured 86 upon your second sampling. Approximately how many total grizzlies did you capture in your second sampling?

299

You are hired by the U.S. Fish and Wildlife Service to determine the density of bullfrogs in a series of five perfectly square ponds. At each pond, you sample both the number of bullfrogs and the length of one side of each pond, and you record these observations in the following table: What is the average number of bullfrogs per square meter in these five ponds?

3.2; see pic

You are examining the population dynamics of a butterfly metapopulation consisting of five highly suitable habitat patches of varying size and quality within a matrix of less suitable habitat. Within each patch, you record the number of individuals present when you began your study, as well as the average number of individuals that die and are born each year over the course of a decade. Finally, you estimate the maximum number of individuals that the patch can sustain given the resource availability and consumption rates of the individuals within each patch. With these data, you make the following table: If the birth and death rates of each patch remain fairly consistent for the future, which patch in this metapopulation is most likely to become the first source population?

5; see pic

A childhood friend and you are walking by a pond that you used to play in as kids. He claims to have counted the crayfish in the pond and bets you that there are 145. You take the bet and agree to do a mark-recapture survey to settle the bet. You grab some chest waders and a net and collect 79 crayfish in half an hour. You place a small dab of fingernail polish on each crayfish and put it back in the pond. You come back several weeks later, and using the same sampling techniques as before, you collect 115 crayfish. Approximately how many of these crayfish would have to be marked for your friend to win the bet?

63

Researchers in Texas are trying to determine the rate of decline of a particular bat population resulting from a recently introduced disease-causing pathogen. The researchers conduct a mark-recapture survey over a period of four years and record their data in a table. Approximately how fast is this bat population declining?

70 bats per year; see pic

You are observing in two separate field habitats the distribution of five herbaceous plant species that require the same resources. You have previously documented that habitat patch A has approximately 140 percent higher levels of resources than habitat patch B. You take a census of individuals from all five species in both habitat patches and record your results in the following table: In which species is a barrier to dispersal, such as the presence of herbivores, most likely limiting the dispersal of individuals into an ideal free distribution?

A; see pic

A researcher is studying the impact of climate change on the geographic ranges of the dominant plant species of the shortgrass prairie and the tallgrass prairie. The researcher selects one shortgrass prairie site in eastern Colorado and one tallgrass prairie site in central Kansas. Blue grama (Bouteloua gracilis) is the dominant plant of the shortgrass prairie. Big bluestem (Andropogon gerardii) is the dominant plant of the tallgrass prairie. Both sites have similar soils and topography but differ in their climate. Mean annual precipitation (MAP) at the shortgrass prairie site is 325 mm and mean annual temperature (MAT) is 9°C. MAP at the shortgrass site is 840 mm and MAT is 13°C. By performing a multiyear garden transplant study in which blue grama individuals are planted in Kansas and big bluestem individuals are planted in Colorado, the researcher ascertains conditions under which each species thrives best. Blue grama does the best when MAP ranges from 300 to 550 mm and MAT ranges from 8°C to 11°C. Big bluestem does best when MAP ranges from 525 to 950 mm and MAT ranges from 10°C to 15°C. Assume that each species' fundamental niche will stay the same as it was when the study was performed, and suppose that 100 years from now the MAP and MAT change at both sites. The MAP becomes 535 mm at the Colorado site and 940 mm at the Kansas site, and the MAT becomes 10.5°C at the Colorado site and 14.5°C at the Kansas site. Based on the findings from the researcher's garden transplant study, how do you think the geographic ranges of the two species will likely be affected?

Blue grama will stay within its current geographic range, and big bluestem will expand its geographic range westward.

True or false? Among scientists, there is a general consensus that resource distribution should cause a species' abundance to decrease as its geographic range increases.

False

True or false? Beginning in the 1940s, forest fire suppression in the Ozark Mountains facilitated dispersal for the regional collared lizard population to newly suitable habitats.

False

True or false? Mark-recapture surveys allow scientists to count every individual in a population

False

In _____dispersion, the position of each individual is independent of the position of other individuals in the population.

Random

_____ dispersion is the null dispersion model of populations against which all other types of dispersion must be tested to determine whether they differ significantly.

Random

What is the best explanation for why the emerald ash borer did not reach North America until the 1990s?

The Pacific Ocean was an effective barrier to dispersal until a ship carried the ash borer from Asia to North America.

What is NOT a common reason individuals in a population do not distribute themselves according to the ideal free distribution?

There are too many individuals for equal per capita distribution of benefits.

Which statement most accurately describes a cosmopolitan species?

a species whose very large geographic range, which can span multiple continents, makes it less susceptible to natural disasters

Beginning in 1994, controlled fires were used to restore habitat suitability for collared lizards in the Ozark Mountains, and as a result the lizards' _____ and their geographic range _____

abundance increased; expanded

Beginning in 1994, controlled fires were used to restore habitat suitability for collared lizards in the Ozark Mountains, and as a result the lizards' _____ and their geographic range _____.

abundance increased; expanded

You are asked by a lake management group to estimate the density of an invasive submerged aquatic plant per square meter along the bottom of a very large lake. You need to know the approximate number of shoots per meter squared in the lake to calculate the appropriate concentration of an herbicide to control the plants. As you study the lake, you determine that the invasive plant occupies a large portion of the bottom of the lake, and where it occurs, it always grows in approximately the same high density. Because the water is clear, you can use aerial measurements to estimate the total lake-bottom area occupied by the plant. What would be the best type of survey for determining the approximate density of plant shoots in this lake?

area-based

The _____ model of a population's spatial structure assumes that all habitat patches are of equal quality.

basic metapopulation

Which technique do researchers use to count every individual in a population?

census

You are a pelican searching for fish in the ocean from high in the sky. Although you see no tasty fish in the open ocean, you soon pass over a series of protected lagoons around an island. Each lagoon contains lots of your favorite fish. As you begin descending into one lagoon, you notice that the fish are aggregated into several schools. Some of these schools are close to each other, while others are far apart, and you cannot determine any consistent pattern in the distance between the schools. As you descend even closer to the water above a single school, you notice that each fish is approximately the same distance from each other fish. Beginning from where you first saw the fish, describe, in order, what patterns of dispersion you noticed the fish exhibiting.

clustered → random → evenly spaced

You are walking through a forest understory when you come across an oak tree. You look at the forest floor and see many hundreds of acorns on the ground around the tree, but as you walk away from the tree, you notice fewer and fewer acorns until you eventually come to another tree, around which you observe the same pattern. Next, you come across a weedy understory plant whose wind-borne seeds will begin germinating wherever they land. Some of these seeds land close together; others land far from any other seeds. Finally, you see a vegetatively reproducing plant with an extensive root system that sends up a shoot approximately every 0.25 meters in every direction. In order, which patterns of dispersion did you observe on your walk from these plants that use very different mechanisms of dispersal?

clustered, random, evenly spaced

You are studying the dispersion of six dandelion individuals in a small field population. In a table, you record the distance between each individual (rows) and every other individual in the population (columns): The six individuals in this small population appear to exhibit _____ dispersion.

clustered; see pic

What is NOT a factor that influences a species' fundamental niche?

disease

The movement of individuals from one area to another is referred to as _____.

dispersal

Inhospitable habitat that keeps a population from extending into suitable habitats is called _____.

dispersal limitation

What is NOT one of the five important characteristics of population distributions?

distension

In general, individuals living in sink subpopulations _____.

do not produce enough offspring to replace themselves

In general, individuals living in sink subpopulations _____

do not produce enough offspring to replace themselves.

The range of conditions predicted to be suitable for a species is called a(n) _____.

ecological envelope

Natural disasters and other disturbances are a major concern for the persistence of _____.

endemic species

True or false? Source-sink metapopulation models are more realistic than basic metapopulation models and landscape metapopulation models.

false

true or false? Mark-recapture surveys allow scientists to count every individual in a population.

false

Decreasing an animal population is generally predicted to decrease the population's geographic range because _____.

fewer individuals will disperse to marginal habitats.

The abundance of a population generally increases as its _____.

geographic range increases

Relatively narrow strips of suitable habitat that connect large patches of suitable habitat are called _____.

habitat corridors

An endemic species is more at risk of going extinct than many other species because endemic species _____.

have only a single, often isolated, geographic range

The lifetime dispersal distance is most useful for predicting _____.

how fast a population will increase its geographic range.

You are going over the results of an experiment examining the impact of habitat corridors on the dispersal ability of bullfrogs. In your study, you placed 100 bullfrogs in a central pond and examined how many of the frogs wound up in each of five peripheral ponds. The peripheral ponds are equal to each other except for the type of habitat corridor connecting them with the central pond. You recorded the following data: If you were to build a new pond and connect it to the central pond, what type of habitat corridor would you use to maximize bullfrog dispersal?

humid forest; see pic

In mark-recapture surveys, a species' total population size is estimated by multiplying the number of _____ by the number of _____ and dividing by the number of _____.

individuals captured and marked in the first survey; individuals captured in the second survey; marked individuals recaptured in the second survey

Researchers who tie a string between two fixed points and count the number of individuals of a plant species that the string crosses are performing a(n) _____ survey of the plant population.

line-transect

The Christmas bird count is conducted every December by volunteers who spend a day following a predetermined path that covers a 24-km circle and counting the number of different bird species they see or hear within the circle. The Christmas bird count is considered a(n) _____ survey.

line-transect

If you were trying to determine the abundance of a large migratory songbird population in Connecticut, what would be the best approach?

mark-recapture survey

Which species would you expect to have the highest density?

mice

Generally, populations contain the highest density of individuals _____.

near the center of their geographic range

An ideal free distribution occurs when all individuals in a population have _____ and distribute themselves _____.

perfect knowledge of habitat variation; to achieve equal per capita benefits

You are conducting a research project examining the spatial structure and movement of an endangered forest-dwelling bird species across the fragmented landscape where it is endemic. During your study, you collect data on the type and amount of resources available for the bird in all forest patches throughout its geographical range. In each of these forest patches, you also carefully document the immigration and emigration of individuals, colonization of new patches, and extinction events. If these are the only data that you collect, you are using the _____ model.

source-sink metapopulation

You are in charge of a project to reintroduce five wildflower species to a mountainside where they are known to have grown but have been locally extinct for years. You have individuals of all five species, but you are not sure exactly where on the mountain each was. To help you determine where each species will grow best, you identify five sites with distinct abiotic and biotic conditions and you plant a few individuals of each plant species at each site. For the next year, you quantify the growth rate in centimeters per year of each species at each site, and you obtain the following data: Assuming that each species has a similar maximum growth rate when it is in its ideal environment, which two species appear to have similar realized niches with respect to this mountain ecosystem?

species B and E; see pic

An isolated patch of individuals within a greater set of populations is called a(n) _____.

subpopulation

What is NOT a condition that typically causes animal populations to exhibit clustered dispersion?

territorial individuals

The landscape metapopulation model differs from all other metapopulation models because it considers _____

the quality of the matrix surrounding suitable habitats

The landscape metapopulation model differs from all other metapopulation models because it considers _____.

the quality of the matrix surrounding suitable habitats

True or false? The geographic range of the emerald ash borer has expanded rapidly in the United States, largely from unintentional human assistance.

true

If you were trying to estimate the abundance of zooplankton (small, free-swimming aquatic invertebrates) in a pond, what would be the best approach?

volume-based survey

The lifetime dispersal distance is the average distance that an individual moves from where it _____ to where it _____.

was born; reproduces

The concept of a species' ecological envelope is similar to its realized niche, except that an ecological envelope describes _____, whereas a realized niche describes _____

where a species could live; where a species does live

The concept of a species' ecological envelope is similar to its realized niche, except that an ecological envelope describes _____, whereas a realized niche describes _____.

where a species could live; where a species does live