Question 1

Which of the following exert bottom-up control?

Accepted Answer

E

Question 2

A trophic cascade implies the presence of

Accepted Answer

A trophic cascade typically implies the presence of top-down control, where predators at the top of the food chain affect the density or behavior of their prey, which in turn affects the next lower trophic level, and so on down the chain.

Question 3

What system provides evidence to support the idea of bottom-up control?

Accepted Answer

Bottom-up control refers to ecosystems being regulated by nutrient availability and primary production. Fertilizer increasing water hyacinth nutrient levels and beetle abundance is an example of bottom-up control, as it shows how nutrient input at the base of the food web can influence higher trophic levels.

Question 4

The idea that predators control herbivore numbers, which in turn permits increased plant growth, is known as

Accepted Answer

The green earth hypothesis posits that predators regulate herbivore populations, thereby allowing for greater plant growth. This concept emphasizes the role of top-down control in ecosystems, where predators limit the number of herbivores, reducing pressure on plant communities and enabling them to flourish.

Question 5

Cod feed on small fish and crabs, which in turn feed on large bodied zooplankton. Zooplankton in turn feed on phytoplankton which themselves use up nitrates in the water. If cod were overfished which organisms should decrease?

Accepted Answer

The answer of Cod feed on small fish and crabs,...

Question 6

Charles Krebs and colleagues applied three different treatments to populations to snowshoe hares: control (1), add fertilizer to increase growth of food plants (3), keep out mammalian predators by electric fences (2), and keep out predators together with added fertilizer (11). The numbers in parentheses represent the resultant numbers of hares relative to control numbers. What can you conclude?

Accepted Answer

The answer of Charles Krebs and colleagues applied three different...

Question 7

In the Serengeti grasslands, star grass density controls the numbers of Thompson's gazelle, which in turn affects lion density. If lions are removed, what happens to the density of Thompson's gazelles?

Accepted Answer

The answer of In the Serengeti grasslands, star grass density...

Question 8

According to the ecosystem exploitation hypothesis, in a system with plants and herbivores, what factor limits the number of herbivores?

Accepted Answer

The answer of According to the ecosystem exploitation hypothesis, in...

Question 9

The environmental stress hypothesis suggests predation causes the highest levels of mortality under __________ environmental stress.

Accepted Answer

The environmental stress hypothesis suggests that predation causes the highest levels of mortality under low environmental stress because in such conditions, prey populations can grow, making them more visible and accessible to predators. In contrast, high environmental stress can directly limit prey populations, reducing the opportunities for predation.

Question 10

Key factors are often

Accepted Answer

The answer of Key factors are often
...

Question 11

If logN_t=2.0 and logN_t+1=1.8 then the killing power or k factor of the mortality is

Accepted Answer

The killing power or k factor of the mortality is calculated as the difference between the log values given, which is 2.0 - 1.8 = 0.2.

Question 12

The key factor in the life cycle of the oak winter moth is

Accepted Answer

Overwintering loss is the key factor in the life cycle of the oak winter moth because it is the stage at which the population is most vulnerable to mortality.

Question 13

If there are four sources of mortality in a population and k₁ = 0.2, k₂ = 0.1, k₃ = 0.8, and k₄ = 0.4, what is K?

Accepted Answer

The answer of If there are four sources of mortality...

Question 14

In a population of moths, if predation and parasitism are both density dependent, overwintering loss is density independent and disease is inversely density dependent, what is likely the key factor?

Accepted Answer

The answer of In a population of moths, if predation...

Question 15

What are the main pupal predators of the oak winter moth?

Accepted Answer

Beetles and shrews are known to be significant predators of the pupae of the oak winter moth, helping to control their population.

Question 16

The part of the generational mortality that would not occur if the mortality factor in question was removed is known as

Accepted Answer

Indispensable mortality refers to the portion of mortality that would not occur if a specific mortality factor were removed, highlighting its essential role in the overall mortality rate.

Question 17

Of 1,000 Colorado beetle eggs, 700 are killed by predatory bugs. Of the resultant 300 larvae, 200 are eaten by birds. Of the resultant 100 pupae, 60 are killed by shrews, leaving 40 adults. What is the percent indispensable mortality at the larval stage?

Accepted Answer

Indispensable mortality at the larval stage is calculated by the formula: [(initial number - final number) / initial number] * 100. Here, the initial number of larvae is 300, and the final number after birds eat 200 of them is 100. So, the calculation is [(300 - 100) / 300] * 100 = 66.6%. However, this calculation represents the total mortality at the larval stage, not the indispensable mortality. Indispensable mortality refers to the mortality that must occur to reduce the population to the number that can be supported by the environment (the number that reaches adulthood in this context, which is 40). Since 200 larvae are eaten by birds, reducing the number from 300 to 100, and only 40 are needed to reach the adult stage, the indispensable mortality at the larval stage is calculated based on the excess larvae that needed to be removed to achieve the final adult population. This means that the indispensable mortality is actually related to how the reduction at the larval stage contributes to achieving the final adult population size, not just the simple percentage reduction at that stage. The question seems to be asking for a specific value related to the larval stage's contribution to overall mortality necessary to reach the final adult population, but the provided calculation and choices do not directly correspond to the concept of indispensable mortality as typically defined. Therefore, the correct interpretation of indispensable mortality in this context is not straightforward from the provided options, suggesting a possible misunderstanding in the question's formulation or in the interpretation of the term "indispensable mortality."

Question 18

Predators have a direct effect on herbivores and an indirect effect on plants.

Accepted Answer

Predators directly affect herbivore populations by preying on them, which in turn indirectly benefits plant communities by reducing the grazing pressure on them.

Question 19

Plants have an indirect effect on herbivores and a direct effect on plants.

Accepted Answer

Plants have a direct effect on herbivores through providing them with food and nutrients, and they have a direct effect on other plants through competition for resources like light, water, and nutrients.

Question 20

Competition would likely limit the number of secondary carnivores in a four trophic level system.

Accepted Answer

In a four trophic level system, secondary carnivores (third trophic level) compete for resources (primary carnivores or herbivores in the second trophic level), and this competition can limit their numbers due to the limited availability of food resources.

Quiz 16: Population Regulation