Ecology help-competition, coevolution questions, and lotka-volterra:

Question

Competitive release is most likely to occur when a:
A.Species colonizes an island that already has potential competitors
B.Species moves into new habitats that it never occupied on a mainland
C.Species decreases in abundance
D.Competing species is added to a community

 

In a graph that plots prey population (Nprey) on the x-axis against the number of predator offspring produced per unit of time on the y-axis, the slope represents the
A.Efficiency of predation (c)
B.Efficiency with which food is converted into predator population growth or reproduction (b)
C.Predator population growth rate (r)
D.The rate of increase in prey availability

 

In the basic Lotka-Volterra equations that describe predator-prey interactions, the growth rate of the prey population (dNprey/dt) is zero when the density of predators (Npred) is equal to:
A.r/N
B.N/r
C.r/c
D.c/r

The net outcome of predator-prey interactions in the basic Lotka-Volterra models is that
A.The predator drives its prey to extinction and then goes extinct itself
B.The prey population declines and this causes the predator population to also decline
C.Predator and prey populations eventually converge on equilibrium population sizes that are maintained into infinity
D.Predator and prey populations oscillate, with each predictably increasing and decreasing in response to the other

In a simple experiment involving only predator and prey with no refuge,

A,Prey will always survive

B.Predators will typically drive their prey to extinction
C.Both populations will oscillate
D.Prey populations will oscillate

Huffaker's experiment involving oranges showed:

A.Predators will always consume prey to extinction
D.Prey will always outlast predators
C.With enough complexity, predator and prey populations will oscillate
D.Both species use oranges for refuge

Answer 1

Question #1:

1. Correct answer: B - Species moves into new habitats that it never occupied on a mainland
2. Reasoning: Competitive release happens when a species, freed from competition, expands its niche (its role and use of resources in the environment). If a species moves to a new habitat where its usual competitors are absent, it can use a wider range of resources or expand into areas it couldn't occupy before. This process is highly-consistent with the principle of competitive release.

Question #2:

1. Correct answer: B - Efficiency with which food is converted into predator population growth or reproduction (b)
2. Reasoning: In the Lotka-Volterra predator-prey model, parameter b is the conversion efficiency—how well predators turn prey biomass into their own offspring. A higher slope means predators reproduce more per prey consumed. In other words, if you plot prey consumed (or prey population size) on the x-axis and predator reproduction on the y-axis, the slope tells you how much predator reproduction you get per unit of prey. This directly reflects the efficiency of converting prey into predator population growth.

Question #3:

1. Correct Answer: C - r/c
2. Reasoning: The Lotka-Volterra prey equation is typically written in the form: dN_prey / dt = rN_prey - cN_prey N_pred , where rN_prey represents the intrinsic growth rate of the prey and cN_prey N_pred represents the rate at which predators consume prey, where “c” is the predation rate. The prey population growth rate (dN_prey / dt) is zero when rN_prey = cN_prey N_pred. If we divide both sides by N_prey (assuming N_prey > 0), we get r=cN_pred. Solving for N_pred, we find N_pred = r/c. This is the predator isocline, the density of predators at which the prey population neither grows nor declines.

Question #4:

1. Correct answer: D - Predator and prey populations oscillate, with each predictably increasing and decreasing in response to the other
2. Reasoning: classic Lotka-Volterra model predicts stable, cyclical oscillations between predator and prey populations. As prey numbers increase, predator numbers eventually increase due to more food. This increased predation then causes the prey numbers to decline, which subsequently leads to a decline in predator numbers due to less food, allowing the prey population to recover, and the cycle repeats. These oscillations are out of phase with each other, as one party’s movement in one direction then triggers movement by the other. Mutual growth cannot occur simultaneously in this context.

Question #5:

1. Correct Answer: B - Predators will typically drive their prey to extinction
2. Reasoning: In highly simplified, closed systems with no environmental complexity or refuge for the prey, predators often overexploit prey, consuming them to extinction. Once the prey is gone, the predators also starve and go extinct. Real systems often require complexity or spatial structure for stable coexistence, as very simple predator-prey systems without these mechanisms are unstable. In many cases, these mechanisms include refuges, immigration, or environmental heterogeneity that allow coexistence.

Question #6:

1. Correct Answer: C - With enough complexity, predator and prey populations will oscillate
2. Reasoning: Huffaker used mites and oranges to show that spatial complexity (like barriers and dispersal aids) can enable sustained oscillations in predator-prey systems.. In simple setups without complexity, the prey were quickly eliminated, and predators quickly drove the prey to extinction. The experiment is famous for showing how environmental heterogeneity promotes stability.