Question 1

Under positive density dependence, population growth rate

Accepted Answer

Under positive density dependence, the growth rate of a population increases as the population becomes larger because individuals cooperate and share resources, leading to increased survival and reproduction. This results in a positive feedback loop, where increasing population size leads to even faster population growth.

Question 2

Which reflects density-independent population regulation?
I. a winter storm that kills birds with equal probability regardless of bird abundance
II. a drought that kills a higher proportion of plants when there are many plants and a smaller proportion when there are fewer plants
III. a lethal disease that is more easily transmitted when animals are found in high abundance than in low abundance

Accepted Answer

Density-independent factors, such as a winter storm that kills birds with equal probability regardless of their numbers, affect a population regardless of its size. Option II describes a density-dependent factor, as drought kills a higher proportion of plants when there are many plants and a smaller proportion when there are fewer plants. Option III also describes a density-dependent factor, as a lethal disease is more easily transmitted when animals are found in high abundance than in low abundance.

Question 3

Consider a biologist studying a population of deer. At the beginning of the year, there are 100 adult deer in the population. Over the course of the year, 15 adult deer die, and an additional 25 deer are born. What can we conclude about λ for this year?

Accepted Answer

The population increased from 100 to 110 (100 - 15 + 25), indicating growth. λ, the growth rate, is greater than 1 when the population increases.

Question 4

Which is likely to follow an exponential increase in population size?
I. a population of mice that has consumed most of the food in its habitat
II. a small population of rats recently introduced to an island with many resources
III. bacteria recently placed on a new Petri dish with suitable growth medium

Accepted Answer

A small population of rats introduced to an island with many resources and bacteria on a new Petri dish with suitable growth medium both have abundant resources, allowing for exponential growth.

Question 5

Which reflects negative density dependence?
I. A fungus infects and kills plants at a higher rate when they are abundant than when they are rare.
II. A group of birds has a higher per capita survival rate when it is large than when it is small.
III. A large population of deer exhausts local food supplies and has a high risk of death; a small population has plentiful food and low risk of death.

Accepted Answer

The answer of Which reflects negative density dependence?
I. A fungus...

Question 6

Use this figure for questions 2 and 3.
 
-Which plot is consistent with an exponential growth model when r > 0?

Accepted Answer

Exponential growth occurs when the rate of change of a quantity is proportional to the current amount, leading to a J-shaped curve that rises steeply as time progresses.

Question 7

Which illustrates a negative relationship between population density and the average size of individuals over time?

Accepted Answer

A self-thinning curve shows a negative relationship between population density and individual size over time. As population density increases, there is more intraspecific competition for resources, leading to smaller individuals.

Question 8

Describe how the geometric growth model is different from the exponential growth model. For each growth model, give an example of an organism that fits the growth pattern it describes. Explain why the organism fits the model.

Accepted Answer

The answer of Describe how the geometric growth model is...

Question 9

The intrinsic growth rate, r, is

Accepted Answer

The intrinsic growth rate, r, is the highest possible per capita increase in population size under ideal conditions. It does not take into account limiting factors such as resources, predation, and competition, and therefore is not the maximum population size that can be supported by the environment. It also does not directly calculate the number of new individuals produced or time it takes for a population to double in size.

Question 10

Use this figure for questions 2 and 3.
 
-Which plot is consistent with a geometric growth model in which λ = 1?

Accepted Answer

The answer of Use this figure for questions 2 and...

Question 11

Negative density dependence occurs when the

Accepted Answer

Negative density dependence occurs when the per capita population growth rate decreases as population becomes larger. This is usually due to competition for resources, increased predation or disease transmission.

Question 12

In a population growing according to the exponential growth model, population size is

Accepted Answer

In the exponential growth model, population size is not limited by environmental factors, implying an ideal, unlimited environment. This model assumes that resources are abundant, allowing the population to grow exponentially without constraints.

Question 13

The Allee effect describes

Accepted Answer

The Allee effect is a phenomenon where populations of certain species have a positive density-dependent growth rate at low population sizes but a negative density-dependent growth rate at high population sizes. This means that at low population sizes, having more individuals can actually increase the fitness of the population, but at high population sizes, having more individuals can result in reduced fitness. Therefore, the Allee effect describes positive density-dependent population regulation.

Question 14

A species of louse (an external parasite) infests salmon. Researchers have found that the lice have difficulty finding a mate when there are only a few lice on an individual fish. The lice find mates more easily and produce more offspring when there are many lice on an individual fish. This is an example of

Accepted Answer

Positive density-dependent population regulation occurs when population growth is limited or regulated by the density of a population. In this case, the lice have difficulty finding a mate when there are only a few of them on an individual salmon, but they are able to find mates more easily and produce more offspring when there are many of them on the same individual salmon. This is because the density of lice on the salmon affects their ability to find and mate with other lice.

Question 15

In the exponential growth model, which term indicates the intrinsic rate of increase?

Accepted Answer

In the exponential growth model, the term that indicates the intrinsic rate of increase is denoted by the letter "r", which represents the per capita growth rate of a population in the absence of any limiting factors.

Question 16

In what way is the geometric growth model different from the exponential growth model?

Accepted Answer

The geometric growth model uses regular time intervals, while the exponential growth model is continuous. Carrying capacity is not included in either model.

Question 17

According to the exponential growth model, which would reduce a population's doubling time?

Accepted Answer

The exponential growth model states that a population's size will increase over time if the intrinsic growth rate (r) is greater than zero. Doubling time is the time it takes for a population to double in size. The formula for doubling time is 0.7/r. Therefore, an increase in the intrinsic growth rate, as stated in choice C, would reduce the doubling time, leading to a faster population growth. Conversely, a decrease in the intrinsic growth rate, as stated in choice D, would increase the doubling time, slowing down population growth. The initial population size, as stated in choices A and B, does not affect the intrinsic growth rate and, therefore, would not directly affect the doubling time.

Question 18

Define population doubling time. Starting with the model for exponential population growth, explain how to derive the formula for population doubling time.

Accepted Answer

The answer of Define population doubling time. Starting with the...

Question 19

Which reflects positive density-dependent population regulation?
I. Small populations of flowers produce fewer seeds per individual than large populations of flowers.
II. Large groups of birds are better able to detect and avoid predators than small groups of birds.
III. The probability that a squirrel will be killed by a forest predator does not depend on the size of the squirrel population.

Accepted Answer

Positive density-dependent population regulation occurs when the fitness or survival of individuals increases with population density. Both I and II describe scenarios where individuals benefit from being in larger groups, either through increased reproductive success or enhanced predator detection.

Question 20

According to an exponential growth population model, when the number of births is less than the number of deaths,

Accepted Answer

In an exponential growth population model, r represents the growth rate of the population. When the number of births is less than the number of deaths, it means that there is a decrease in the population size, which leads to a negative population growth rate. Therefore, the correct choice is A, r < 0.

Quiz 12: Population Growth and Regulation