Q: Using the logistic growth equation $$G = rN \left( \frac{K-N}{K} \right)$$, if the carrying capacity $$K$$ for wildebeest is 1,200,000, the current population $$N is 600$$,000, and the per capita rate of increase $$r is 0.02$$, what is the population growth rate $$G$$?

$$G = 0.02 \times 600,000 \left( \frac{1,200,000-600,000}{1,200,000} \right) = 0.02 \times 600,000 \times 0.5 = 6,000$$

Question 1

Which of the following best describes the type of population growth observed in the Serengeti wildebeest population after the eradication of rinderpest, as shown in the graphs provided?

Accepted Answer

Exponential growth, followed by logistic growth as the population approaches carrying capacity.

Question 2

Using the logistic growth equation $$G = rN \left( \frac{K-N}{K} \right)$$, if the carrying capacity $$K$$ for wildebeest is 1,200,000, the current population $$N is 600$$,000, and the per capita rate of increase $$r is 0.02$$, what is the population growth rate $$G$$?

Accepted Answer

$$G = 0.02 	imes 600,000 \left( \frac{1,200,000-600,000}{1,200,000} ight) = 0.02 	imes 600,000 	imes 0.5 = 6,000$$

Question 3

Which of the following is a density-independent factor that could affect wildebeest populations in the Serengeti?

Accepted Answer

A severe drought that reduces water availability.

Question 4

Based on the predation vs. herbivore weight graph, which of the following statements is most accurate?

Accepted Answer

Smaller herbivores experience higher rates of predation compared to larger herbivores.

Question 5

In Robert Paine’s experiment, what happened to the diversity of species when starfish were removed from the intertidal zone?

Accepted Answer

Species diversity decreased significantly, with mussels dominating the area.

Question 6

Which of the following best explains why starfish are considered a keystone species in their ecosystem?

Accepted Answer

Their presence maintains species diversity by controlling mussel populations.

Question 7

According to the green world hypothesis, what is the primary reason the world remains 'green' in many ecosystems?

Accepted Answer

Predators control herbivore populations, preventing overgrazing of plants.

Question 8

In the kelp-urchin-otter-orca food web, what was the effect of orcas beginning to prey on sea otters?

Accepted Answer

Sea otter populations decreased, sea urchin populations increased, and kelp density decreased.

Question 9

Which of the following statements about trophic cascades is supported by the Letourneau and Dyer experiment with piper plants, ants, caterpillars, and beetles?

Accepted Answer

Adding predatory beetles reduced ant populations, increased caterpillar populations, and decreased plant leaf area.

Question 10

If a population is being sustainably harvested, at what population size $$N is $$the maximum sustainable yield achieved according to the logistic growth model $$G = rN \left( \frac{K-N}{K} \right)$$?

Accepted Answer

At $$N = \frac{K}{2}$$, where the growth rate $$G is $$maximized.

Question 11

Which of the following is NOT a plausible outcome of removing a keystone predator from an ecosystem?

Accepted Answer

Stabilization of the ecosystem with increased species diversity.

Question 12

Which of the following best describes the effect of density-dependent factors on population growth?

Accepted Answer

They increase in effect as population density increases, limiting growth through mechanisms like competition and predation.

Question 13

In the context of the Serengeti wildebeest, which factor was most responsible for the rapid population increase after 1960?

Accepted Answer

Eradication of rinderpest, a density-independent disease.

Question 14

Which of the following scenarios best illustrates a top-down control in an ecosystem?

Accepted Answer

Removal of a predator leads to an increase in herbivores and a decrease in plant biomass.

Question 15

Why does the percentage of wildebeest deaths due to predation decrease as herbivore body weight increases, according to the predation vs. weight graph?

Accepted Answer

Larger herbivores are less vulnerable to predation due to their size and defensive behaviors.

Question 16

Which of the following statements about keystone species is FALSE?

Accepted Answer

Keystone species are always the most abundant species in their ecosystem.

Study Guide: Population Dynamics and Trophic Cascades in Ecology

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