Question 1

Which statement correctly identifies the relationship between population size and extinction risk?

Accepted Answer

Small populations are more susceptible to genetic and demographic factors that can lead to extinction, such as inbreeding and environmental stochasticity. In contrast, larger populations have more genetic diversity and a greater capacity to resist and recover from environmental disturbances. Therefore, population size is negatively correlated with extinction risk.

Question 2

Which of the following is most likely to explain why Daphnia exhibits greater oscillations in population size than Bosmina?

Accepted Answer

Delayed density dependence occurs when population growth is limited by actions taken by individuals in the population, such as resource depletion or aggression. Daphnia is known to exhibit this pattern, whereas Bosmina does not. This can lead to greater oscillations in Daphnia populations as compared to Bosmina populations.

Question 3

Variation in birth and death rates due to random differences among individuals is

Accepted Answer

Demographic stochasticity refers to random variations in birth and death rates among individuals in a population. Overshooting the carrying capacity, environmental stochasticity, and habitat fragmentation are different concepts that do not specifically relate to random variations in birth and death rates.

Question 4

The females of a certain species of fish produce on average 1,000 eggs each year. By chance some females produce a few more eggs than average, and others produce slightly fewer eggs than average. This is an example of

Accepted Answer

The variability in egg production is an example of demographic stochasticity, which refers to random fluctuations in birth and death rates that occur due to chance events rather than environmental factors. In this case, some females just happen to produce more or fewer eggs than the average without any environmental influence.

Question 5

Consider these two populations, which exhibit variation in population size over time. In which population is the fluctuation most likely due to environmental variation, and in which population is fluctuation most likely due to density dependence? Explain your answer.

Accepted Answer

The answer of  Consider these two populations, which exhibit...

Question 6

Variations in birth and death rates due to random changes in environmental conditions are

Accepted Answer

Environmental stochasticity refers to random fluctuations in environmental conditions that can affect birth and death rates of populations. The other choices do not accurately describe this phenomenon.

Question 7

Of the following species, which is most likely to exhibit a stable limit cycle or dampened oscillations?

Accepted Answer

The species in option C is likely to exhibit dampened oscillations or a stable limit cycle because of its dependence on limited juvenile food resources. This could lead to fluctuations in adult fecundity and survival, which could create cyclical fluctuations in population size. The other options are less likely to exhibit limit cycles or oscillations because they do not involve cyclical dependencies or feedback loops.

Question 8

Two species of mice are similar in many characteristics. However, species A has large fat reserves that increase survival over periods when environmental resources are depleted, while species B has no fat reserves. Which species is more likely to exhibit oscillating population dynamics? Explain your answer.

Accepted Answer

The answer of Two species of mice are similar in...

Question 9

Consider the time series of population sizes in years 1 and 2 for populations a, b, c, and d. If the population size in year 3 is determined by a logistic model with delayed density dependence from a 1-year time lag , r = 1, and K = 10 individuals, which of the following time series of population sizes would lead to an overshoot of the carrying capacity in year 3?

Accepted Answer

The logistic model with delayed density dependence considers the population size from the previous year. In option A, the population grows from 5 to 10 individuals, reaching the carrying capacity. With r = 1, the growth rate is high enough to cause an overshoot in year 3.

Question 10

Consider a population with the following numbers of individuals over time. year 1: 10
Year 2: 25
Year 3: 30
If the population size in year 4 is determined by a logistic model with delayed density dependence from a 1-year time lag and K = 50 individuals, what value of r would lead the population size to exceed carrying capacity in year 4?

Accepted Answer

We can use the logistic equation with delayed density dependence to determine the population size in year 4, given the population sizes in years 1-3: Nt = K / [1 + (K / N(t-1)) * e^(-rt)] Plugging in the values given, we get: N4 = 50 / [1 + (50/30) * e^(-r)] To find the value of r that leads to the population exceeding carrying capacity in year 4, we need to solve for N4 > 50: 50 / [1 + (50/30) * e^(-r)] > 50 This simplifies to: 1 + (50/30) * e^(-r) < 1 e^(-r) < -20/50 r > ln(50/20) r > 0.916 The only answer choice that satisfies this inequality is D, r = 2.0. Therefore, choice D is the correct answer.

Question 11

Which is an example of demographic stochasticity?
I. increased moose mortality when the population exceeds carrying capacity
II. variation in death rate of mice due to chance differences between individuals
III. increases and decreases in seed production due to changes in rainfall

Accepted Answer

Demographic stochasticity refers to fluctuations in population size resulting from random events affecting births and deaths within a population. Option II describes such variation in death rate of mice due to chance differences between individuals, making it the correct choice. Option I refers to environmental stochasticity, which involves fluctuations in birth and death rates arising from environmental factors. Option III also refers to environmental stochasticity, specifically due to changes in rainfall affecting seed production. Therefore, the best choice is B - II only, as it captures an example of demographic stochasticity.

Question 12

Consider four populations of island birds. Each island has a different carrying capacity, and the birds are subject to environmental and demographic stochasticity. Which population is LEAST likely to go extinct?

Accepted Answer

A larger carrying capacity (K) typically means a population can support more individuals, which increases the likelihood of survival during periods of environmental or demographic fluctuation. Therefore, island 4 with a carrying capacity of 1,200 is the least likely to go extinct.

Question 13

For populations growing under the logistic growth model with delayed density dependence, which of the following combinations of parameter values is most likely to lead to damped oscillations?

Accepted Answer

Damped oscillations in populations under the logistic growth model with delayed density dependence are more likely when the intrinsic growth rate (r) is relatively high, the carrying capacity (K) is large, and the delay (τ) is moderate to high. Option C, with r = 0.5, K = 200, and τ = 3, combines a higher growth rate with a significant delay and a large carrying capacity, conditions that favor the emergence of damped oscillations.

Question 14

Which population model incorporates random variation in population growth?

Accepted Answer

Stochastic population models incorporate random variation in population growth, while deterministic models assume a constant, predictable growth rate. Stable limit models assume a stable population size without fluctuations, and metapopulation models describe a network of interconnected subpopulations.

Question 15

Consider a population with the following numbers of individuals over time. year 1: 100
Year 2: 150
Year 3: 200
Year 4: 250
If the population size in year 5 is determined by a logistic model with delayed density dependence, r = 1.1, and K = 200 individuals, what value of  $ \tau $ would cause the population to decrease from year 4 to year 5?

Accepted Answer

The logistic model with delayed density dependence is given by:Nt+1 = Nt + rNt(1 - Nt/K) - F1F1F1S1F1F1F10Nt-1If the population size in year 5 is to decrease from year 4, then Nt+1 < Nt. Substituting Nt = 250 and Nt+1 = Nt - 1 into the equation, we get:250 - 1 = 250 + 1.1*250*(1 - 250/200) - F1F1F1S1F1F1F10*250Solving for F1F1F1S1F1F1F10, we get:F1F1F1S1F1F1F10 = 0

Question 16

Explain the biological reason that higher intrinsic growth rates and longer delays lead to greater oscillations in population size.

Accepted Answer

The answer of Explain the biological reason that higher intrinsic...

Question 17

A biologist is developing models to describe the population dynamics of the species he studies. Four models are listed. Each model is based on the logistic model, with r equal to 1 and K equal to 100. The initial population size is given by N₀. In which of his models of population growth would the population be most likely to go extinct?

Accepted Answer

Stochastic models incorporate randomness and are more realistic in predicting the likelihood of extinction, especially for small initial populations like N₀ = 10.

Question 18

A species of grass is affected by the amount of rainfall in the spring. In years of high rain, the grass survives better than in years of low rain. This is an example of

Accepted Answer

The fact that the survival of the grass is affected by the amount of rainfall in the spring indicates that the population dynamics of the grass are impacted by environmental stochasticity, which refers to random fluctuations in environmental factors that affect population size and structure.

Question 19

Which is an example of environmental stochasticity?
I. changes in the weather that increase or decrease survival by a small amount
II. variation in individual health that affects likelihood of death
III. forest fires that kill large numbers of individuals every 10 to 50 years

Accepted Answer

I represents environmental variation that does not have catastrophic consequences but can impact individuals to some degree. III represents sudden catastrophes that kill off large numbers of individuals. Both of these are examples of environmental stochasticity. II, on the other hand, represents individual-level variation that is not strictly environmental stochasticity, as it is not caused by external forces but rather internal ones.

Question 20

Which type of model always includes random variation?

Accepted Answer

Stochastic models incorporate random variation into their structure, whereas deterministic models do not. The terms logistic and exponential refer to specific types of mathematical functions that can be used to model relationships between variables, but these models can be either stochastic or deterministic depending on whether or not they incorporate random variation.

Quiz 13: Population Dynamics Over Space and Time