Population Ecology

Population ecologists are primarily interested in understanding how biotic and abiotic factors influence the density, distribution, size, and age structure of populations. the overall vitality of a population of organisms. how humans affect the size of wild populations of organisms. studying interactions among populations of organisms that inhabit the same area. how populations evolve as natural selection acts on heritable variations among individuals and changes in gene frequency. Answer: a 2

Population ecologists are primarily interested in understanding how biotic and abiotic factors influence the density, distribution, size, and age structure of populations. the overall vitality of a population of organisms. how humans affect the size of wild populations of organisms. studying interactions among populations of organisms that inhabit the same area. how populations evolve as natural selection acts on heritable variations among individuals and changes in gene frequency. 3

Dispersion patterns tend to be highly dependent on the spatial scale of the observer. For example, football players lined up on the scrimmage line are clumped at the scale of 100 yards but uniformly dispersed at the scale of a meter. An example of animals that are likely to be clumped at a large scale but uniformly distributed at a small scale is buffalo grazing on a prairie. bluegills swimming in a northern lake. ant nests in an abandoned field. red-winged blackbirds in a cattail marsh. all of the above. Answer: e 4

Dispersion patterns tend to be highly dependent on the spatial scale of the observer. For example, football players lined up on the scrimmage line are clumped at the scale of 100 yards but uniformly dispersed at the scale of a meter. An example of animals that are likely to be clumped at a large scale but uniformly distributed at a small scale is buffalo grazing on a prairie. bluegills swimming in a northern lake. ant nests in an abandoned field. red-winged blackbirds in a cattail marsh. all of the above. 5

Imagine that a species of fish used to be a broadcast spawner (producing many eggs that then get no subsequent parental care) but has evolved to be a mouth brooder (holding the eggs in the parent’s mouth until they hatch and then caring for the young for a while). We would expect the survivorship curve of this species to shift from Type I to Type II or III. shift from Type II to Type I. shift from Type III to Type I or II. shift from Type II to Type III. vary unpredictably. Answer: c 6

Imagine that a species of fish used to be a broadcast spawner (producing many eggs that then get no subsequent parental care) but has evolved to be a mouth brooder (holding the eggs in the parent’s mouth until they hatch and then caring for the young for a while). We would expect the survivorship curve of this species to shift from Type I to Type II or III. shift from Type II to Type I. shift from Type III to Type I or II. shift from Type II to Type III. vary unpredictably. 7

The exponential growth model describes the increase in population size of a population that is not constrained by resources or space. The graph shows the elephant population in Kruger National Park, which appears to have been reproducing exponentially from 1900 to 1963. From this graph, you can tell that none of the elephants died. a female elephant living around 1960 was more likely to have a baby than a female elephant living around 1920. the elephants adapted to the new park conditions around 1955. the vegetation the elephants eat could support more than 5,000 elephants. the more elephants there are, the more tourists will visit the park. Answer: d 8

The exponential growth model describes the increase in population size of a population that is not constrained by resources or space. The graph shows the elephant population in Kruger National Park, which appears to have been reproducing exponentially from 1900 to 1963. From this graph, you can tell that none of the elephants died. a female elephant living around 1960 was more likely to have a baby than a female elephant living around 1920. the elephants adapted to the new park conditions around 1955. the vegetation the elephants eat could support more than 5,000 elephants. the more elephants there are, the more tourists will visit the park. 9

You do a study on elephants and find that there are eight elephants per acre. This is a measurement of density. dispersal. demographics. survivorship. Answer: a 10

You do a study on elephants and find that there are eight elephants per acre. This is a measurement of density. dispersal. demographics. survivorship. 11

A population of deer grows from 100 to 200 to 600, and when it gets to 600, it levels off. This population must have reached exponential growth. carrying capacity. logistic growth. Answer: b 12

A population of deer grows from 100 to 200 to 600, and when it gets to 600, it levels off. This population must have reached exponential growth. carrying capacity. logistic growth. 13

Which of the following statements is not an assumption of the logistic model of population growth? Populations adjust instantaneously to growth. Populations approach carrying capacity smoothly. An S-shaped growth curve results when N is plotted over time. The growth rate increases as N approaches K. Answer: d

Which of the following statements is not an assumption of the logistic model of population growth? Populations adjust instantaneously to growth. Populations approach carrying capacity smoothly. An S-shaped growth curve results when N is plotted over time. The growth rate increases as N approaches K.

What is the difference between semelparity and iteroparity? Semelparous organisms return to their place of birth to reproduce, but iteroparous organisms can reproduce anywhere. Semelparous refers only to plants, but iteroparous refers to animals. Semelparous organisms live after their first reproduction, but iteroparous organisms die. Semelparous organisms die after their first reproduction, but iteroparous organisms are capable of repeated reproduction. Answer: d

What is the difference between semelparity and iteroparity? Semelparous organisms return to their place of birth to reproduce, but iteroparous organisms can reproduce anywhere. Semelparous refers only to plants, but iteroparous refers to animals. Semelparous organisms live after their first reproduction, but iteroparous organisms die. Semelparous organisms die after their first reproduction, but iteroparous organisms are capable of repeated reproduction.

Assume U.S. energy use is 300 GJ per capita and Chinese energy use is 27 GJ per capita. If the U.S. population is 313 million people and the Chinese population is 1.3 billion people, the total U.S. energy use is approximately how many times greater than the total Chinese energy use? 10 100 0.5 3 6 Answer: d

Assume U.S. energy use is 300 GJ per capita and Chinese energy use is 27 GJ per capita. If the U.S. population is 313 million people and the Chinese population is 1.3 billion people, the total U.S. energy use is approximately how many times greater than the total Chinese energy use? 10 100 0.5 3 6

Scientific Skills Exercise In the logistic population growth model, the per capita rate of population increase approaches zero as the population size (N) approaches the carrying capacity (K), as shown in the table. Assume that rmax = 1.0 and K = 1,500. You can then calculate the population growth rate for four cases where population size (N) is greater than carrying capacity. To do this, use the equation for population growth rate in the table.

Which population size has the highest growth rate? Answer: a

Which population size has the highest growth rate?

If rmax is doubled, how would the population growth rates change? The population growth rates would be half of what they were. The population growth rates would double. The population growth rates would be unchanged. The population growth rates would be four times what they were. Answer: b

If rmax is doubled, how would the population growth rates change? The population growth rates would be half of what they were. The population growth rates would double. The population growth rates would be unchanged. The population growth rates would be four times what they were.

What does a negative population growth rate tell you about the dynamics of the population? The birth rate equals the death rate. The population size is increasing instead of decreasing. The population size is decreasing instead of increasing. Answer: c

What does a negative population growth rate tell you about the dynamics of the population? The birth rate equals the death rate. The population size is increasing instead of decreasing. The population size is decreasing instead of increasing.

The red line shows the growth predicted by the logistic model, and the black dots show the measured growth of the population. Does the measured growth match the predicted growth pattern? No; only a few of the black dots sit on the red line. Yes; it matches at the beginning and at the end of the time range. No; it is lower than the predicted values in some parts and higher in other parts. Yes; it matches over the whole time range. Answer: c

The red line shows the growth predicted by the logistic model, and the black dots show the measured growth of the population. Does the measured growth match the predicted growth pattern? No; only a few of the black dots sit on the red line. Yes; it matches at the beginning and at the end of the time range. No; it is lower than the predicted values in some parts and higher in other parts. Yes; it matches over the whole time range.

What is the predicted carrying capacity of the Daphnia culture? 120 Daphnia/50 mL 135 Daphnia/50 mL 200 Daphnia/50 mL Answer: b

What is the predicted carrying capacity of the Daphnia culture? 120 Daphnia/50 mL 135 Daphnia/50 mL 200 Daphnia/50 mL

Did the Daphnia population ever experience a negative growth rate? From about day 70 to day 105, the population decreased in size, indicating a negative growth rate. The population never experienced a negative growth rate because it stabilized after 140 days and never went to zero. From about day 20 to day 50 and from day 100 to day 150, the population fell below the predicted values, indicating a negative growth rate. Answer: a

Did the Daphnia population ever experience a negative growth rate? From about day 70 to day 105, the population decreased in size, indicating a negative growth rate. The population never experienced a negative growth rate because it stabilized after 140 days and never went to zero. From about day 20 to day 50 and from day 100 to day 150, the population fell below the predicted values, indicating a negative growth rate.

What is the best biological explanation for why the Daphnia population growth rate became negative between days 70 and 105? The population’s data defined by the black dots have a slope that is negative during that period. The population grew larger than the predicted size during that period. The population overshot the carrying capacity and started running out of resources during that period. The population’s death rate was greater than the birth rate during that period. Answer: c

What is the best biological explanation for why the Daphnia population growth rate became negative between days 70 and 105? The population’s data defined by the black dots have a slope that is negative during that period. The population grew larger than the predicted size during that period. The population overshot the carrying capacity and started running out of resources during that period. The population’s death rate was greater than the birth rate during that period.

Between days 100 and 160, the Daphnia population dropped below the predicted carrying capacity before rising back up to it. What is the best biological explanation for why the population stayed below the carrying capacity between days 100 and 160? The predicted carrying capacity is incorrect. It really should be 120 Daphnia/50 mL, where the population stabilized during those 60 days. After the population overshot the carrying capacity, the debris from dying Daphnia prevented the population from increasing until the debris decomposed, which took 60 days. Overcrowding before day 100 caused the birth rate to decrease and the death rate to increase, and it took another 60 days for the relative rates to stabilize. Daphnia decided to limit population growth until they figured out how large a population they could support in the culture, which took 60 days. Answer: c

Between days 100 and 160, the Daphnia population dropped below the predicted carrying capacity before rising back up to it. What is the best biological explanation for why the population stayed below the carrying capacity between days 100 and 160? The predicted carrying capacity is incorrect. It really should be 120 Daphnia/50 mL, where the population stabilized during those 60 days. After the population overshot the carrying capacity, the debris from dying Daphnia prevented the population from increasing until the debris decomposed, which took 60 days. Overcrowding before day 100 caused the birth rate to decrease and the death rate to increase, and it took another 60 days for the relative rates to stabilize. Daphnia decided to limit population growth until they figured out how large a population they could support in the culture, which took 60 days.