51. Community Ecology

Community Structure

Ecological succession: Life Returns to Mt. St. Helens

Which of the following could qualify as a top-down control on a grassland community?
a. limitation of plant biomass by rainfall amount
b. influence of temperature on competition among plants
c. influence of soil nutrients on the abundance of grasses versus wildflowers
d. effect of grazing intensity by bison on plant species diversity

SCIENTIFIC THINKING An ecologist studying plants in the desert performed the following experiment. She staked out two identical plots, which included a few sagebrush plants and numerous small, annual wildflowers. She found the same five wildflower species in roughly equal numbers on both plots. She then enclosed one of the plots with a fence to keep out kangaroo rats, the most common grain-­eaters of the area. After two years, to her surprise, four of the wildflower species were no longer present in the fenced plot, but one species had increased dramatically. The control plot had not changed. Using the principles of ecology, propose a hypothesis to explain her results. What additional evidence would support your hypothesis?

Draw a vertical food chain (part of a food web) showing that sea urchins eat kelp and that sea otters eat sea urchins. Use this model to (1) show or explain how a trophic cascade works; and (2) offer an explanation for why otters are considered a keystone species.<img src="https://lightcat-files.s3.amazonaws.com/problem_images/1b8606f861981e22-1672933323446.jpg" alt="" />

Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in inset, among red blood cells) which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term, if not treated. Why is Lyme disease on the rise in eastern North America?

Researchers have measured a positive correlation between forest fragmentation and incidence of Lyme disease. According to the theory of island biogeography, how do you predict fragmentation will affect species richness?

Ecological Succession

A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods.

Rather than measuring the entire 6000-hectare (ha) forest, the researchers sampled arthropod diversity by intensively collecting as many arthropods as they could in 12 plots that measured 20 m×20 m square. If 1 ha=10,000 m2,, how many hectares of forest did they sample in all?
a. 20 m×20 m×12=4800 ha

b. 4800 m2×10,000 m2/1 ha=48,000,000 ha

c. 20 m×20 m=400 ha

d. 4800 m^2 x 1ha/10,000 m^2 = 0.48 ha

2.4 Trophic Levels & Energy Flow

Climatic changes lead to reduced water availability.

No. This choice refers to geologic processes that may be responsible for a disturbance, but not to community succession.

Most populations have a limited life span and die, making room for others.

No. Populations do not necessarily have a limited life span.

No. To a greater or lesser extent resources are always limited.

No. One of the listed responses is correct.

Each existing community changes the environment.

Consider the impact of each community on its surroundings.

Why does succession of communities occur?

No. This answer is too specific. Consider what the length of seasons, especially the length of the growing season, affects. Also consider that water availability is only one of several important climatic factors.

No. Evolutionary history is one key factor. Altitude does affect the second key factor.

No. Both of these choices relate to the key factor climate. Evapotranspiration is the evaporation of water from soil plus the transpiration from leaves. However, neither evapotranspiration nor temperature accounts for the time that species have had to develop in certain regions of the world.

No. Both of these are climatic factors. Evolutionary history also is a key factor.

Think of the difference in species richness near the equator compared to the polar caps. Which of the choices would most likely account for this difference?

What are two key factors in species richness equatorial&#150;polar gradients?

Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in inset, among red blood cells) which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term, if not treated. Why is Lyme disease on the rise in eastern North America?

White-footed mice occupy a broad ecological niche—they occur in most communities regardless of habitat quality. Many other species, like the opossum, are absent from low-quality forest fragments. Based on this information and the data in Question 12, propose a hypothesis to explain the observed relationship between increased forest fragmentation and increased incidence of Lyme disease.

According to the island equilibrium model, species richness would be greatest on an island that is
a. large and remote.
b. small and remote.
c. large and close to a mainland.
d. small and close to a mainland.

Learn Biology: Trophic Levels and Producer vs. Consumer

No. Only about 10% of the energy stored in the organic matter of each trophic level is converted to organic matter at the next trophic level.

Only about 10% of the biomass energy of an organism is converted to biomass at the next trophic level. .

A field contains 950 kg of plant material. How many kilograms of tertiary consumers could be supported?

Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in inset, among red blood cells) which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term, if not treated. Why is Lyme disease on the rise in eastern North America?

A letter to the editor in a local newspaper asserts that “we cannot afford to preserve natural forests, because we need to use these resources to help humans.” How could you respond to this comment in terms of Lyme disease?

No. Wind is not one of the largest influences on potential evapotranspiration.

No. Soil type is not one of the largest influences on potential evapotranspiration.

No. Slope is not one of the largest influences on potential evapotranspiration.

No. Season is not one of the largest influences on potential evapotranspiration.

Review the concept of potential evapotranspiration.

The potential evapotranspiration is determined by __________.

In Southeast Asia, there’s an old saying: “There is only one tiger to a hill.” In terms of energy flow in ecosystems, explain why big predatory animals such as tigers and sharks are relatively rare.

Ecological Succession-Primary and Secondary

Process of Ecological Succession | Primary & Secondary Succession Concept

Keystone Species | Ecology

Learn Biology: Keystone Species vs Indicator Species

Trophic Levels-Energy Flow in Ecosystems

Vegetation consists of sphagnum bogs on poorly drained flat areas.

No. This does happen during ecological succession on a glacial moraine, but not for about 300 years. This is long after the pioneer species have paved the way for spruce and hemlock trees.

Decomposition of acidic spruce needles reduces the pH of the soil.

No. This does happen during ecological succession on a glacial moraine, but not for several centuries. Remember that spruce trees are unlikely to be a pioneer species.

Alder forms dense thickets up to 9 meters tall.

No. This does occur, but alder are not pioneer species.

Bare soil is acidic because of the carbonate compounds in the parent rocks.

No. The carbonate compounds in parent rocks would make the bare soil basic, not acidic.

Low nitrogen content causes many plants to have yellow leaves.

Consider the plant nutrient that must be "fixed" in the soil.

Which of the following statements correctly describes conditions on a glacier moraine during the reign of pioneer species?

There are fewer lions in Africa’s Serengeti than there are zebras. This is principally because                   .
a. zebras tend to drive off lions;
b. lions compete directly with cheetahs, whereas zebras do not have any competitors;
c. zebras have mutualists that increase their population, whereas lions do not;
d. there is less energy available in zebras to support the lion population than there is in grass to support the zebras;
e. zebras are a keystone species, whereas lions are not

Disturbance

Biogeography and Species-Area Curve

Community 1 contains 100 individuals distributed among four species: 5A, 5B, 85C, and 5D. Community 2 contains 100 individuals distributed among three species: 30A, 40B, and 30C. Calculate the Shannon diversity (H) for each community. Which community is more diverse?

Natural Disturbances

Which of the following organisms is mismatched with its trophic level?
a. algae—producer
b. phytoplankton—primary consumer
c. carnivorous fish larvae—secondary consumer
d. eagle—tertiary or quaternary consumer

No. Because of increasing geographic area, there will be a corresponding addition of habitats. This addition of habitats will lead to an increase in the number of species present.

The area of the community is not involved in determining the number of species present.

No. Geographic area does influence the number of species present.

Review the Alexander von Humboldt idea of the species-area curve.

What happens to the number of species in a community as the area of that community increases?

According to the generalized species-area curve, when habitat is reduced to 50% of its original size, approximately                    of the species once present there will be lost.
a. 10%;
b. 25%;
c. 50%;
d. 90%;
e. it is impossible to estimate the percentage

A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods.

By comparing the number of arthropod species that were common among the 12 plots sampled, the researchers estimated that the total number of arthropods in the whole San Lorenzo forest is 25,000 species. To come up with this estimate, what’s one assumption the researchers had to make about the forest?

Trophic Levels and Food Webs

Species Area Curves Island Biogegraphy

What is a disturbance? Consider the role of fire in a forest. Compare the consequences of high-frequency versus low-frequency fire, and high severity versus low severity of fire.

A group of populations living in close enough proximity to interact regularly

No. This is the definition of a community.

A species that kills and eats another species

No. This is the definition of a predator.

A species that is killed and eaten by another

A type of interspecific interaction that benefits both species

No. This is the definition of a mutualism.

Consider that patho refers to disease.

Which of the following is the definition of a pathogen?

Species Diversity and Islands AP Biology 54.4

Glacier Bay Alaska

Theory of Island Biogeography

Species Area Curve

Trophic Levels

No. Equilibrium refers to species number, not number of individuals.

No. Disturbance is not considered in the hypothesis. Different levels of disturbance can affect species numbers.

No. Food webs emerge from trophic interactions that are not related to island biogeography.

No. Species number can remain the same, even in the face of extinction, as long as immigration continues.

the rate of species immigration will equal the rate of species extinction

Review the MacArthur and Wilson hypothesis.

When equilibrium is reached on an island, __________.

"In a classic study, John Teal measured energy flow in a salt marsh ecosystem. The table below shows some of his results.
a. What percentage of the energy in sunlight was converted into chemical energy and incorporated into plant biomass? What term describes this new biomass?
b. What percentage of the energy in plant biomass was incorporated into the bodies of the primary consumers? What became of the rest of the energy (see Figure 37.16A)?
c. How much energy is available for secondary consumers? Based on the efficiency of energy transfer by primary consumers, estimate how much energy will be available to tertiary consumers." <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/d73d068b3121511d-1677810811609.jpg" style="width: 478px;">

BI124: Disturbances and Succession

The North American pronghorn looks and acts like the antelopes of Africa. But the pronghorn is the only survivor of a family of mammals restricted to North America. Propose a hypothesis to explain how these widely separated animals came to be so much alike.

Predators that are keystone species can maintain species diversity in a community if they
a. competitively exclude other predators.
b. prey on the community’s dominant species.
c. reduce the number of disruptions in the community.
d. prey only on the least abundant species in the community.

Biology video on Species Area Relationship part1

(OLD) Unit 7 Ecology Ecological Succession Notes

Ecological Succession (Theme 1 Topic 1 pg 5)

Food chains are sometimes short because
a. only a single species of herbivore feeds on each plant species.
b. local extinction of a species causes extinction of the other species in its food chain.
c. most of the energy in a trophic level is lost as energy passes to the next higher level.
d. most producers are inedible.

Island Biogeography

Activity 1 - Trophic Structure and Food Webs

Trophic Structure

2.3 Island Biogeography

The feeding relationships among the species in a community determine the community’s
a. secondary succession.
b. ecological niche.
c. species richness.
d. trophic structure.

Based on the intermediate disturbance hypothesis, a community’s species diversity is increased by
a. frequent massive disturbance.
b. stable conditions with no disturbance.
c. moderate levels of disturbance.
d. human intervention to eliminate disturbance.

A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods.

The graph below shows some of the data for the major arthropod groups collected. Notice that the scale on the y axis is logarithmic to make both small and large numbers legible on the same graph. For example, there are about 400 species of spiders, but only 40 species of bees. About how many arthropods were found in total? About what percentage of these were beetles? <img src="https://lightcat-files.s3.amazonaws.com/problem_images/a9d219e780756c51-250521.jpg" alt="" /><img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/0ee98bd0f00b3260-1677308217678.jpg" style="width: 300px;">

Disturbances

About a third of insect species measured are in decline, meaning that their populations are shrinking due to habitat destruction, pollution, and other factors. Predict how this change affects the bee pollination of crops such as apples and almonds.

That they eventually reach a state of equilibrium

No. This type of model is applicable to an older view of biological communities.

That they maintain a relatively constant composition of species

No. The nonequilibrium model describes communities as constantly changing after being buffeted by disturbances.

That the effect of disturbances is usually negative

No. This is not always true. Disturbances may create opportunities for species that have not previously occupied habitats to become established.

That disturbance and nonequilibrium are the norm

Consider Florida during the hurricane season.

What is the current view of biological communities?

The most plausible hypothesis to explain why species richness is higher in tropical than in temperate regions is that
a. tropical communities are younger.
b. tropical regions generally have more available water and higher levels of solar radiation.
c. higher temperatures cause more rapid speciation.
d. diversity increases as evapotranspiration decreases.

Pioneer species tend to have high                 and lower survivorship.

Ecological Succession, Human Disturbances, and Biodiversity

Keystone Species

1.9 Trophic Levels

No. Although zoonotic pathogens do infect many species, they specifically infect humans, too.

A pathogen that can be controlled with antibiotics

No. Antibiotics control only bacterial pathogens.

No. Zoonotic pathogens infect more than one species (at least one of which is humans).

No. Many modern zoonotic diseases are not easily treatable: mad cow and hantavirus, for example.

A pathogen that is transferred from another species to humans

Consider that "zoo-" refers to animals.

What is a zoonotic pathogen?

Ecosystem Disturbances vs. Stability

Suppose that a two-acre lawn on your college’s campus is allowed to undergo succession. Describe how species traits, species interactions, and the site’s history might affect the community that develops.

Which of the following best illustrates ecological succession?
a. A mouse eats seeds, and an owl eats the mouse.
b. Decomposition in soil releases nitrogen that plants can use.
c. Grasses grow in a deserted field, followed by shrubs and then trees.
d. Imported pheasants increase in numbers, while local quail disappear.

Key Species and Enviornmental Disturbances

A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods.A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods.

Use the data in the graph to analyze the following statements. Select True or False for each statement, then correct any false statements to make them true.
T/F All taxa shown in the graph are insects.
T/F All taxa shown in the graph have segmented bodies and limbs.
T/F All taxa shown in the graph are terrestrial.
T/F If the researchers had sampled for mollusks, they probably would have found almost as many species as they did for arthropods.

Energy Flow in Ecosystems

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