AP Biology : Understanding Ecosystems

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #11 : Ecology

Why is negative feedback inhibition important when it comes to containing population sizes?

Possible Answers:

Negative feedback inhibition sustains populations and allows them to continue increasing in size 

Negative feedback inhibition prevents populations from continually increasing in size

Negative feedback inhibition is density independent and sustains populations in the face of environmental challenges

Negative feedback inhibition continually supplies populations with resources necessary for life 

Negative feedback inhibition is density dependent and sustains populations in the face of environmental challenges

Correct answer:

Negative feedback inhibition prevents populations from continually increasing in size

Explanation:

Negative feedback inhibition prevents populations from continually increasing in size. Without these such factors, population sizes would not be controlled. For example, perch feed on and find shelter in kelp. Where there are too many perch, there is not enough kelp to sustain them all (for food and shelter), and the fish population decreases in size. When there are less perch, there is enough kelp for them to feed on and hide in. Because conditions are favorable, the perch numbers increase. This negative feedback inhibition is density dependent and controls population size dynamics. 

Example Question #11 : Ecology

K-selection is to r-selection as __________ is to __________.

Possible Answers:

Exponential growth is to logistic growth 

dispersion . . . metapopulations

semelparous . . . iteroparous

life tables . . . cohorts 

density . . . demography 

Correct answer:

semelparous . . . iteroparous

Explanation:

K-selection is density dependent selection, while r-selection is density independent selection; the two are opposites. While all the answer choices are related, only one displays the same (opposite) relationship: semelparous and iteroparous.  Semelparous refers to the “one shot” reproductive trend, producing many offspring only once during an organism's lifetime. Iteroparous refers to organisms that breed multiple times, producing few offspring each time. For semelparous organisms, survival is low and the environment is generally unpredictable. For iteroparous organisms, survival rates are high and the environment is stable and dependable.  

Example Question #13 : Ecology

Resources are being widely consumed and are becoming scarce. When looking at a graph that shows the relationship between resources and population size, what might one expect the graph to look like?

Possible Answers:

Logistic growth model 

Type 2 survivorship curve

Type 1 survivorship curve

Exponential growth model 

Type 3 survivorship curve

Correct answer:

Logistic growth model 

Explanation:

The logistic growth model shows that population size levels off as it approaches its carrying capacity. In this situation, as the population increases and resources are used, the population approaches its carrying capacity, which is the maximum population size that the environment can support. The exponential growth model is unrealistic, as it shows a population’s growth when resources are abundant, but this there is no environment where resources are always in abundance. Survivorship curves show the life patterns of species; rather than comparing the relationship between resources and population size, these types of graphs compare age and population size.  

Example Question #11 : Ecology

Which of the following factors determine the distribution of the earth's habitats and ecosystems?

I. Air circulation

II. Rainfall

III. Topography

IV. Microbiological factors

V. Reproduction rates

Possible Answers:

I, II and IV

I, II, and III

I, III, and V

II, III, IV, and V

II, IV, and V

Correct answer:

I, II, and III

Explanation:

The earth's habitats and ecosystems are dispersed based on air circulation, rainfall, and topography. For example, when looking at the globe, we may notice that the world's major grasslands are always leeward of major mountain ranges, or that tropical rain forests are located around the equator. Why do grasslands fall on the leeward side of mountain ranges, and tropical rainforests at the equator? As the air travels up the mountain, it condenses and precipitation occurs. Once the air reaches the leeward side, it is dry, resulting in the grasslands and plains. Tropical rainforests are located at the equator, an area that gets constant sunlight and rainfall regardless of the earth's tilt. The dispersion of the earth's habitats and ecosystems is very dependent on such environmental factors.  

Example Question #11 : Understanding Ecosystems

Which pattern of dispersion is a result of territoriality?

Possible Answers:

Random dispersion 

Uniform 

Emigration 

Clumped

Demography 

Correct answer:

Uniform 

Explanation:

A clumped pattern of dispersion occurs when individuals aggregate in patches. For example, a herd of cows all graze in a field together, as it is their only source of food within five miles. Uniform dispersion is when organisms are evenly spaced throughout a given area. This results from territoriality, or when organisms defend their physical space against other organisms. Random dispersion is the unpredictable spacing of organisms throughout a given area. There are no strong attractions or repulsions among individuals that would result in clumped or uniform dispersion; the animals are scattered randomly.  

Example Question #12 : Ecology

Life tables are created to show survival patterns in a population. They are created based on the observations of which of the following?

Possible Answers:

Reproductive rates

Dispersion 

Emigration 

Immigration 

Cohorts

Correct answer:

Cohorts

Explanation:

Life tables are summaries of the survival patterns of a population. They are constructed using cohorts (groups of individuals of similar age). By following and observing these individuals from birth until death, researchers can make life tables and plot survivorship cures, showing the number of cohorts alive over their lifetimes.

Example Question #17 : Ecology

Which statement about iteroparity is false?

Possible Answers:

Adults are likely to survive and breed

Iteroparity is favored in dependable environments

There are few offspring but they live to survive and reproduce 

Competition for resources is intense 

Few adults reproduce, but those that do reproduce only once in their lifetimes and in abundance 

Correct answer:

Few adults reproduce, but those that do reproduce only once in their lifetimes and in abundance 

Explanation:

Iteroparity refers to an organism's reproductive strategy that involves multiple reproductive cycles. Adults are likely to survive and breed, each time producing few offspring. They care for their young, who grow to adulthood and also reproduce. In these kinds of environments, competition for resources is very intense. Semelparity refers to an organism's reproductive strategy that involves a single reproductive cycle over the course of its lifetime. Semelparity in associated with mass reproduction, and is favored in highly variable and unpredictable environments. Offspring usually have a low survival rate, and reach sexual maturity quickly. 

Example Question #11 : Ecology

Which of the following describes a community?

Possible Answers:

Multiple organisms interacting 

Abiotic and biotic relationships and interactions in a given area

A group of populations of different species living in the same area and interacting

A variety of organisms of the same species living in the same area and interacting 

Food webs created by the food chains of a given area

Correct answer:

A group of populations of different species living in the same area and interacting

Explanation:

A community is a group of populations of different species but live in the same area and interact. Community interactions may display interspecific interactions such as competition, predation, herbivory, symbiosis, or facilitation. A population is a group of organisms of the same species that live together and interact. 

Example Question #13 : Ecology

Which is not an example of symbiosis?

Possible Answers:

Two organisms live in close proximity and one organism benefits while the other does not

Two organism live intimately but only one organism benefits 

A parasite gets nourishment from its host organism 

One organism preys on another organism 

Two organisms live in close proximity and benefit each other

Correct answer:

One organism preys on another organism 

Explanation:

Symbiosis is when two organisms live in close proximity and usually benefit each other, such as in mutualism. However, this is not always the case. Commensalism is a type of symbiosis and only benefits one of the organisms or has neutral effects. Parasitism is another form of symbiosis, where one organism benefits at the expense of its host. 

Example Question #20 : Ecology

In forest A, moss 1 only grows above the shrubbery, while moss 2 grows below the shrubbery. In forest B (similar to forest A), moss 2 grows both above and the shrubbery; here, moss 1 is non-existent. Which of the following terms refers to the area moss 2 occupies in forest A?

Possible Answers:

Resource partitioning 

Realized niche

Character displacement 

Ecological niche

Fundamental niche

Correct answer:

Realized niche

Explanation:

An ecological niche is the sum of a species’ use of its environment, including both biotic and abiotic factors. Resource partitioning is the differentiation of niches; it is impossible for two species to have the same niche and use the same resources. Resource partitioning allows for differentiation of niches between similar species so they can coexist. A fundamental niche is described in forest B, where moss 2 grows both above and below the shrubbery. It is the niche that could be potentially occupied by a species. The realized niche is the term that refers to the area of moss 2 in forest A. The realized niche is the portion of the fundamental niche that an organism actually occupies. We know that moss 2 can potentially occupy areas above and below shrubbery, but in forest A, it only occupies the area below the shrubbery (its realized niche). 

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