Chapter 16: Ecology

The study of the distribution and abundance of organisms, their interactions with other organisms, and their interactions with their physical environment is called ecology.

The top few meters of soil, the oceans and other bodies of water, and the lower 10 kilometers of the atmosphere are included.

A description of the habitat may include other organisms that live there, as well as the physical and chemical characteristics of the environment.

It means that resources are consumed or the environment is changed in some way by the presence of the organisms when they are said to occupy a particular niche.

Population ecology studies the growth, abundance, and distribution of populations.

There may be 100 buffalo or 100 mosquitos.

They can be clumped, uniform, or random.

It's often expressed in an age structure diagram.

The diagram shows the frequencies of individuals in a particular age group.
A large proportion of the population is young when the population is growing rapidly.
The age structure diagrams with tiers larger at the base and narrower at the top indicate rapidly growing populations.

Mortality is high after that age.

Humans have type I survivorship.

Oysters and other species produce free-swimming larvae that make up a component of marine plankton.

Only the few that survive are grown ups.

Somebacteria can divide in 20 minutes.

In 10 hours, one bacterium could give rise to over a trillionbacteria.
It takes elephants nearly two years to have a single baby.
The weight of the descendants from two elephants would surpass that of the earth after 2,000 years.

parasites and disease, competition for resources, space for growth and reproduction, and the toxic effect of waste products are examples.

Predators are often density- dependent.
When populations reach high densities, reproductive behavior may be abandoned.
Stress may be a limiting factor.

Extremes of climate and natural disasters are common examples.

The net increase in individuals is the numerator of the equation.

The change in the number of individuals is what it means.

The expression can be written in terms of.

When births and deaths are equal, the growth rate is zero and the population size remains constant.

When the population size is large, limiting factors will have a greater effect than when it is small.

A newly introduced population may grow quickly before limiting factors stop it.
The population size may decline to levels lower than the carrying capacity if limiting factors bring it under control.
Population growth may be renewed once reduced below carrying capacity.
A new carrying capacity may be established if the habitat was damaged by the large population.
When the population size is large, limiting factors can have a negative effect on population growth.
Limits exert little negative feedback when the population size is small.

Changes in the number of hares and the number of lynx are followed by changes in the number of lynx.

There are fluctuations between predator and prey.

The population size in hares is related to the amount of available food and the weather.

The age of reproductive maturity, the frequency of reproduction, the number of offspring per reproductive event, and how long the organisms lives are some of the variables that affect reproductive success.

There are many ways in which these four variables can be combined to maximize fitness.

They produce many offspring that are small, mature quickly, and require little or no parental care.

Humans produce a small number of relatively large offspring that need extensive parental care until they mature.

They reproduce frequently during their lifetimes.

The human population grew rapidly about a thousand years ago.

Humans were able to change from a hunter/gatherer lifestyle to one of agriculture by domesticating animals and plants.

The development and application of pesticides and the construction of irrigation systems have led to an increase in food output from agriculture.

The rate of growth was increased because of the discoveries of antibiotics, vaccines, and proper hygiene.

Health risks from human waste were reduced by the development of water purification and sewage systems.

Humans were able to live in environments that were previously unsuitable because of better housing, warmer clothing, and easy access to energy.

Community ecology is concerned with the interaction of people.

One species is likely to be more successful when it competes for the same resources.

The second species is eliminated because one species outcompetes the other.

The principle of competitive exclusion was formulated by a Biologist.

According to Gause, no two species can survive if they occupy the same niche.

One population used resources more efficiently.

The second species was eliminated.

Some species share the same resources.

They occupy niches that are slightly different.
Individuals minimize competition and maximize success by securing their resources in slightly different ways.
Resource partitioning is theDividing up the resources in this manner

Five species of warblers coexist in the same trees by feeding on insects in different parts of the tree.

Realized niche.

One species of barnacle can live on rocks that are exposed to the full range of tides.

The full range from the lowest to the highest tide levels is its fundamental niche.
In the natural environment, a second species of barnacle outcompetes the first species at the lower tide levels, where desiccation is minimal.
The first species only survives at higher tide levels.

Some characteristics may allow individuals to obtain resources in their partition more successfully.

A divergence of features or character displacement can be caused by the selection of these characteristics.

Two species of finches have the same beaks and are suited for the same food supply.

Due to evolution, the beak of each bird species is different on a third island.
Each finch can feed on seeds of a different size.

A predator is any animal that consumes a plant or another animal.

Although the host may be weakened by the parasites, they don't usually die until the parasites have completed at least one life cycle.

After the eggs hatch, the larvae consume the host's tissues.

The host dies, but not until the larvae begin pupation.

Seed eaters act like a predator in that they completely consume the organisms.

There are three forms of symbiosis.

A "+" indicates that one individual benefits, a "-" indicates one is harmed, and a "0" indicates no effect is provided in a shorthand notation.

There are certain trees that provide food and housing for ants.

The resident ants kill any insects found on the tree.
In addition, the ants crop any neighboring vegetation that makes contact with the tree, thereby providing growing space and sunlight for the tree.

Minerals, water, a place to attach, and protection from herbivores are provided by the fungi.

In some cases, the hyphae kill some of the symbiotic algae cells.

Some researchers consider the lichen symbiosis to be closer to parasites.

The flora is fed and protected.

In exchange, the flora helps digest otherwise indigestible foods, produces vitamins K, and prevents the growth of harmfulbacteria, and carries out other beneficial functions.
The flora carries out fermentative processes in order to digest polysaccharides and provide the host with a source of energy and nutrition.
ruminants chew their food to break it down into smaller pieces for more thorough fermentation.
Plants help the fungus by providing sugars to it, and the filaments of the fungus increase the surface area of the roots, facilitating the absorption of water and minerals.
Most flowering plants and conifers form mycorrhizae.

Birds build their homes in trees.

The tree is not helped by the presence of the nest.

There are animals around cattle.

The birds eat insects that are aroused by the cattle.
The cattle are not helped or harmed.

Tapeworms steal food from their hosts.

In the contest between predator and prey, some prey may have unique heritable characteristics that enable them to more successfully escape.

Some predators have characteristics that allow them to more successfully capture prey.
The natural selection of characteristics leads to the evolution of predator and prey.
Two species may evolve so that mutual benefits increase.
Coevolution is the evolution of one species in response to another.

Tannins, commonly found in oaks, and nicotine, commonly found in tobacco, are toxic to herbivores.

In many cases, metabolism has evolved in herbivores that allow them to tolerate toxins.
Monarch butterflies eat milkweed plants that have toxins in their bodies that protect them from their predators.

The fur of the snowshoe hare is white in the winter and brown in the summer.

The colored moths look like bird droppings.

Camouflage is provided by the markings on tigers and other cats.

The yellow-brown coloring of lions provides camouflage.

Plants with the shape and color of the rocks are more likely to escape attack.

The yellow and black bees are seen as a threat by the predator.

Mullerian mimicry is an effective strategy because a single pattern, shared among several animals, is more easily learned by a predator than would be a different pattern for every animal.

There are yellow and black body markings on bees, yellow jackets, and wasp.

Some defenseless flies have yellow and black markings but are avoided by predators because they look like bees.

Only a third of the flower's seeds are eaten by the moths after they hatch from the eggs.

The hummingbirds have long beaks and little sense of smell, but they are attracted to red flowers with no odor.

In exchange for the transfer of their pollen to other flowers, the flowers provide a lot of nectar.

The traditional view of succession shows how one community is gradually replaced by another with different species.

The number of species in a community increases as succession progresses.
The climax community continues until it is destroyed by a fire.

Succession is not as predictable as was thought.

Successional stages may not always occur in the expected order, and the establishment of some species is apparently random, influenced by season, or by which species arrives first.
In some cases, a stable climax community is never attained because of fires and other disturbances occurring so frequently.

When climates change over thousands of years, Succession occurs in some regions.

Succession occurs because species that make up communities change the habitat.
The habitat may be more favorable to new species if the physical and biological conditions that made it attractive to the resident species no longer exist.

Succession is described by a series of plant communities.

Animals take up residence in these communities because of their attraction to the plants in the area, not because of any change in the environment.

Animals affect the physical characteristics of the community by adding organic matter when they leave feces, and by altering the biological characteristics of the community when they consume plants or distribute seeds.

The effects of animals on succession are difficult to determine.

There are many pioneer species that can tolerate harsh conditions.

The growth of plants whose roots support mutualistic relationships with nitrogen-fixing bacteria can be supported by soils deficient in nutrition.

Perennial grasses, herbs, shrubs, and trees are included.

The environmental effects slow down the rate of succession.
It may remain the same for hundreds of years once the climax community is established.

On volcanic islands, lava flows, and on rock left behind by retreating glaciers, primary succession occurs.

The mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the mycelia of the myc After soil accumulates, protists, mosses, and fungi appear, followed by insects and other arthropods.

The new soil is usually deficient in nitrogen.
Next, selected species are established.

Perennial shrubs and trees are included.

The sand is stable after six years.

The dunes of Lake Michigan are where the next stages of this succession can be seen.
The establishment of cottonwoods is followed by the rooting of shrubs.
Over the next 50 to 100 years, pines and black oaks will follow.
The beech-maple community is established.
The entire process may take a long time.

Secondary succession begins in habitats damaged by fire, floods, insect devastations, overgrazing, and forest clear-cutting and in disturbed areas such as abandoned agricultural fields, vacant lots, roadsides, and construction sites.

Secondary succession begins on soil that already supports life.

Grasses and weeds are selected from seeds already in the soil.

The trees that follow are specific to the region.
In some parts of the eastern United States, pines take root next, followed by various hardwoods.

Sand and silt are carried in by a river and contribute to the filling of the lake.

Submerged vegetation is the first to be established.

Grasses, sedges, rushes, and cattails grow at the perimeter of the lake.

After the lake fills with vegetation, it is replaced by a meadow of grasses and herbs.

The meadow is replaced by shrubs and native trees in many mountain regions.

About 1% of the solar energy that reaches the surface of the earth is converted into organic matter.

Understanding how the energy gets distributed to all the living things in an environment helps us understand how the system works.

Two types of flow charts show who eats who.

The arrows show the direction of the energy flow.

It would show the plants and animals that eat them, as well as the animals that eat them.

The food web may include detritivores.

All organisms that are eaten by animals are connected by arrows.

Plants, protists, and cyanobacteria are included.

When the sources of energy are non-inorganic substances, primary producers can be represented.

Other detritivores include worms, insects, and scavengers.

In these unique communities, prokaryotes live in specialized organs of tube worms.

The tube worms absorb dissolved H2S and O2 and transport it to the prokaryotes, where they use the free energy from H2S to produce carbohydrates.

The relative sizes of trophic levels are represented by horizontal bars or tiers.

Energy is transferred between tiers when they are stacked in an order.
Other shapes may also result in a pyramid-shaped figure.

The biomass is available to herbivores.

Much of the energy is lost as heat.

The components are related by an equation.

All of the tiers above it are supported by the bottom tier of the ecological pyramid of energy.

When herbivores eat the primary producers, the energy stored in NPP is transferred to them.
The energy used by the herbivores is used for respiration and the rest is used for growth.
The secondary and tertiary consumers repeat the process above the herbivores, using the energy from the tiers below them to grow.

The relative sizes of tiers in an energy pyramid show the ecological efficiency of the system.

10% of the productivity of one trophic level is transferred to the next level on average.
When an animal or plant dies, the remaining 90% is consumed by the individual activities of that animal or plant.

Much of the energy for respiration and other activities is lost as heat.

The energy that cannot be harnessed by organisms is called heat.
All the energy gained through the program is lost as heat.
In contrast to other forms of matter, heat cannot be recycled.

Most domestic animals used for food or work are herbivores.

The amount of energy required to raise and sustain a carnivore would far surpass its worth in food or work.
The meat that a person consumes would yield a better return if it was used for human food.

A species becomes dominant in its particular habitat because it is best able to compete for resources or escape disease in the community.

Dramatic changes in the makeup of other trophic levels are caused by the removal of a keystone species.

Sea otter eat sea urchins and kelp.

The fish and marine invertebrates that lived in the kelp beds disappear.

The grey wolf is a keystone species that eats large mammals.

Wolves were hunted to extinction because of threats to livestock.
In their absence, the landscape was destroyed and vegetation was over grown.
Smaller mammals diminished as a result of the growth of coyotes.
When wolves were reintroduced to the park, vegetation returned.
The restored vegetation camouflaged the increased numbers of animals near lakes and streams.
The carcasses abandoned by wolves attracted eagles and other meat-eating animals.

The return of wolves restored the balance of living things that were native to the area.

Humans have introduced most of the invaders.

It kills trees and other vegetation by blocking sunlight from reaching leaves.

At the first World's Fair in 1876, it was introduced to the United States.

The bark beetle is spreading the fungus.

The native habitat of the fungus is uncertain, but it was accidentally introduced in Europe and the United States in the early twentieth century.

New fyllal on the leaves can be seen after the fyllal has spread through the plant tissues.

The splays can be dispersed by wind or water.
Potatoes were introduced to Europe in the 16th century and remained disease-free until the 19th century.

The first appearance of the fungus was in the United States, where it was dispersed by wind and then delivered to Europe.

The Native American populations were devastated by the disease because of the lack of immunity in the Western Hemisphere.

Primary producers provide the initial source of energy and their numbers and amount of biomass determine the makeup of all other trophic levels.

A small tier of primary producers can't sustain many tiers above it.

As it passes through the tiers of the pyramid of energy, there is a 10% decline in the amount of energy provided.

The number of trophic levels that can be supported quickly declines.
Longer food chains and more complex food webs can be created by more efficient ecosystems.
Tropical rain forests have such ecosystems.

There are more levels below the top trophic levels that can be weakened by environmental changes.

Large animals with large energy requirements are the top predator in the upper tier.

There is less energy available at the top of the pyramid and so the size of top tiers is limited.

The size of trophic levels can be regulated.

Few trophic levels above primary productivity can be supported.

Primary producers expand without challenge in the absence of herbivores.
At some point, the availability of primary production will lead to an increase in the number of herbivores.
More primary producers are consumed as the number of herbivores increases.
Growth of primary producers is allowed to increase once again because of the predator's response to increasing numbers of herbivores.

The model is not the same as the bottom-up model.

Sea otter occupying the top tier limits the number of sea urchins.
The bottom trophic level of kelp forests increases in numbers when sea urchins are in check.
Sea otter removal will result in an increase in sea urchins and a decrease in kelp forests.
Sea otter regulate the population size of the kelp, the bottom tier.
Humans create many examples of the top-down model when they remove keystone species by overhunting.

The abundance and type of primary producers and the number of species primary production can be influenced by the amount, variability, and form of water.

The range of temperatures throughout the year is equally important.

Solar energy exposure affects the amount of food produced.

The equator gets more solar energy than the poles.
Because seasonal variations are minimized at lower latitudes, more constant environmental conditions are able to support more species.

There are many species in the tropics, but only a small number of each one.

There are many individuals of those species in the polar ecosystems.

The larger the environment, the more likely it is that it contains different types of soil.

A variety of species can be supported by more diverse habitats.

As elevation increases, the temperature decreases.

The water content of snow deposited at higher altitudes is only available to plants after it has melted.

After the snow has melted,iferous forests become productive.

In a highly diverse system, disturbances may affect a few of the components, but one or more unaffected components can replace them.

In systems with low biodiversity, there may be more permanent effects.
Fires, floods, disease, and the effects caused by humans are some of the problems that threaten the stability of the ecosystems.

As the wind blows, it pushes surface water in the same direction, blowing it away from the west coast of South America.

The bottom-up ecological effect is stimulated by the nutrients.
Sea birds eat fish.
When the trade winds and upwelling stop, the local food web and fish industry collapses.
As a result of the carcasses of dead sea animals, many marine invertebrate populations increase in number.
The effects of El Nio stretch from Australia to the southwestern United States.

Both increase the amount of particulate matter in the atmosphere and reduce the amount of solar radiation reaching the surface of the earth.

A decrease in primary production leads to a bottom-up effect.
CO2 is released into the atmosphere by volcanic eruptions.

The last mass extinction occurred 65 million years ago at the K-T boundary.

It could have been caused by a volcanic eruption or asteroid impact.
Most of the species became extinct, including the dinosaurs.

It could have been caused by a volcanic eruption or asteroid impact.

Half of the species became extinct.
Dinosaurs became the dominant fauna after the extinction opened up ecological niches.

Plates have fault lines.

Plates collide and create earthquakes, volcanos, and mountains.
The plates that are moving apart are in the ocean basins.
A long-term isolating mechanism for speciation is the formation of continents arising from the separation of larger plates.
As mountains and volcanos form, environmental conditions change, creating new niches for speciation.

Australia, South America, Africa, and India were once part of a supercontinent called Gondwana.

When the continents separated, mammals on Australia, South America, and Antarctica became isolated from other mammals.
The mammals on the remaining land mass evolved into the placental mammals.

The biogeochemical cycles describe the flow of essential elements from the environment to living things.

The major storage locations for essential elements, the processes through which each element incorporates into plants and animals, and the processes through which each element returns to the environment are outlined in the following list.

Animals drink water or eat other organisms which are mostly water, while plants absorb water from the soil.

Animals and plants break down.

The building of all organic compounds requires carbon.

Plants and animals use CO2 in the same way.

Plants and animals release CO2 when organic material is burned.

Nitrogen is required for the production of nucleic acids.

Nitrogen is obtained by eating plants or other animals.

2 to NO3 can be achieved by lightning and UV radiation.

Various nitrifyingbacteria made 4 to NO2 and NO2 to NO3

Plants convert 4 or NO3 to organic compounds.

Animals andbacteria release nitrogen from their bodies.

3 are converted to N2 by denitrifyingbacteria.

It is necessary for the manufacture of nucleic acids.

The biogeochemical cycles of calcium and magnesium are similar to the phosphorus cycle.

Animals excrete phosphorus in their waste products when they break down.

Population growth, destruction of habitats for agriculture and mining, pollution from industry and transportation, and many other activities contribute to the damage of the environment.

Most of the solar radiation that passes through the atmosphere is visible light.

The atmosphere reflects some of the solar radiation back into space, while the rest is absorbed by the earth.
Some of the radiation comes back into the atmosphere, but it's longer wavelength radiation.
CO2 and other gases are absorbed by the infrared radiation as it passes through the atmosphere on its way out into space.

Fossil fuels are burned for energy as the food and energy needs of the human population rise.

Burning traps more heat.
Global temperatures are rising.
Warmer temperatures raise sea levels, decrease agriculture output, affect weather patterns, increase human disease, and threaten extinction to species, by disrupting the environmental conditions to which species are adapted.

Ozone is formed in the upper atmosphere when UV radiation reacts with oxygen.

The ozone blocks the UV radiation from reaching the surface of the earth, which would cause damage to plants and animals.

chlorofluorocarbons enter the upper atmosphere and break down ozone molecule.

Although their manufacture has stopped, chlorofluorocarbons are still being used as propellants in aerosol sprays and in the manufacture of plastic foams.
UV radiation can reach the surface of the earth when the ozone layer thins.

Fossil fuels and industrial processes release pollutants into the air that contain sulfur dioxide and nitrogen dioxide.

The substances react with water and produce acids.
When these acids return to the surface of the earth, they acidify soils and bodies of water, decreasing pH and adversely affecting plants and animals in lakes and rivers and on land.

The grasslands become deserts as a result of overgrazing.

habitats available to native species are lost as a result of this.

The slash-and-burn method of clearing tropical rain forests increases atmospheric CO2, which contributes to the greenhouse effect.

Burning the forest destroys the nutrients because they are stored in the vegetation.
The soil of some rain forests can only support one or two years of agriculture.

Air pollution, water pollution, and land pollution affect the materials essential to life.

Many pollutants do not degrade quickly and remain in the environment for a long time.
There are subtle ways in which pollution occurs.

A lake can be polluted with sewage.

The oxygen supplies are reduced when the phytoplankton respire.

When the algae die, their bodies are consumed by detritivorousbacteria, which further depletes the oxygen.
Many animals, including fish and invertebrates, are deprived of oxygen due to the result.
Growth rates are balanced when the process occurs naturally.
The accelerated process often leads to the death of fish and the growth of anaerobicbacteria that produce foul-smelling gases.

Plants and animals are becoming extinct at a faster rate than the planet has ever experienced, as a result of human activities, especially the destruction of tropical rain forests and other habitats.

Many of the disappearing plants could become useful to humans if they were to survive.

A review of the material presented in this chapter is provided by the questions that follow.

They can be used to evaluate how well you understand the concepts.
AP multiple-choice questions are often more general, covering a broad range of concepts.
The two practice exams in this book are for these types of questions.

Four possible answers or sentence completions are followed by each of the following questions or statements.

The one best answer or sentence is what you choose.

The age structure diagrams represent four different populations.

A population of 500 experiences 55 births and 5 deaths in a year.

The following key can be used for questions.

The answer in the key can be used more than once.

The burr-bearing seeds that are dispersed by clinging to the fur of mammals do not harm or help the mammals.

Both the monarch and viceroy butterflies have orange wings with black markings.

Both the monarch caterpillar and butterfly are unpalatable and toxic when the monarch caterpillar feeds on milkweed.

Oxpeckers are birds that ride rhinoceroses and other ungulates and eat skin parasites.

The poisonous snakes have bright colors of red, black, and yellow.

Several species of harmless snakes look like poisonous coral snakes.

The following pyramid is referred to in question 18.

The questions that follow are typical of an entire AP exam question or just that part of a question that is related to this chapter.

There are two types of questions on the AP exam.

It takes about 20 minutes to answer a long free-response question.
Sometimes they offer you a choice of questions to answer.
6 minutes is the time it takes to answer a short free-response question.
Don't use bullets or outline form.
diagrams can be used to supplement your answers, but a diagram alone is not adequate.

A fly that does not sting or bite has yellow and black stripes on its body.

Explain the value these markings bring to harmless flies in two or three sentences.

The health of a community is influenced by a keystone species.

The succession of a lake and the eutrophication of a lake can be compared.

The defenseless viceroy butterfly benefits from mimicking the aposematic monarch butterfly.

Both organisms benefit from mutualism.

The oxpeckers get food and the rhinos have parasites removed.

Snakes are Mullerian mimics when they both look alike and have some kind of aposematic defense.

The bright colored harmless snakes are mimics because they benefit from the defense mechanism of the colorful poisonous snakes they resemble.

The species are characteristic of the later stages of succession.

Primary succession takes place on newly exposed substrates.

Secondary succession would be initiated by all of the other choices.

The burning of any organic fuel such as wood, coal, oil, natural gas, and gasoline adds CO2 to the atmosphere.

Nitrogen that plants can't use is converted to gaseous N2 by soilbacteria.

The beginning of a food chain should begin with producers.

The oysters are eating the producers.

The pelicans occupy the top of the food chain.

Many pelican populations were close to extinction before the United States banned the pesticide DDT.

These flies are not real.

By looking like bees and wasp, they fool people into thinking they are dangerous.

Small, simple communities are more likely to have keystone species.

Large, complex communities have many interacting populations, and the removal of one species can be replaced with another species whose niche may be comparable enough to maintain the stability of the community.
keystone species aren't removed without major negative consequences to the community.

The communities that occupy an area are referred to as Succession.

If the process begins on a new surface, it is called primary succession.
It is called secondary succession if it occurs on a lake that has previously supported life.
Each community changes the habitat in a way that makes it more suitable to new species.
Each community has its own growing conditions.
The final, climax community is stable until it is destroyed by fire.
The process begins again.

The characteristics were selected.

Good dispersal ability, rapid growth, and rapid reproduction are some of the characteristics.
The lake is populated by protists, rotifers, mollusks, insects, and other arthropods.

Submerged vegetation is replaced by vegetation that emerges from the surface, covering the surface with leaves.

Plants and animals add organic matter to the lake.
The water from the streams enters the lake.
The lake becomes marshy as it is overrun by vegetation.
When the lake is full, it becomes a meadow with plants and animals that are adapted to a dry environment.
shrubs and trees from the surrounding area invaded the meadow.
The climax community may be a forest consisting of oaks or maples.
The climax community is usually a forest of pines, firs, and hemlocks.

Eutrophication is the increase in the amount of water in a lake.

Eutrophication happens in both unpolluted and polluted lakes.

Eutrophication occurred slowly over a period of many years in the natural succession of the lake.

The chemical and physical nature of the lake allowed for the orderly change of communities, each new community suitable for the new conditions.

Eutrophication can be accelerated by effluent from sewage orfertilizer.

Over a period of months, algae growth occurs.
When they respire at night, algae reduce the amount of oxygen in the air.
When the algae die as shorter winter days approach, rapidly growing aerobicbacteria that feed on the dead algae further deplete the oxygen content of the water.
Plants and animals die in the absence of oxygen.
The dead organisms that fill the bottom of the lake are stimulated by the growth of the anaerobicbacteria that produce foul-smelling sulfur gases.
The surface of the lake may become littered with dead fish.

The AP exam has essay questions about succession.

You can be asked to describe succession for a particular type of habitat, or you can be given a choice of different kinds of successions.
The first paragraph and the beginning of the second paragraph contain general information that applies to all successional processes.
The firstparagraph makes a comparison between unpolluted and polluted lakes, and the secondparagraph makes a contrast between the two.

The competitive exclusion principle results in resource partitioning, character displacement, and realizedniches.

2 to NH4 is caused by nitrogen fixingbacteria that live in the soil or in the root nodules of certain plants.

Some N2 is converted to NO - 3 by lightning.

Denitrifyingbacteria convert NO - 3 back to N2 when they are denitrifying.

Plants make some acids.

Animals get a form of nitrogen that they can metabolize when they eat plants.
Animals produce ammonia when they break down.
Many animals excrete NH3 directly.
Other animals convert NH3 to less toxic forms, such as urea or uric acid.
When plants and animals die, they break down through the process of ammonification, in whichbacteria convert the amino acids and other nitrogen-based compounds to NH + 4, which then becomes available again for plants.

You may be asked to discuss any of the biogeochemical cycles on the AP exam.

The most common request is thenitrogen cycle.
You could use a drawing with arrows to show the various conversions of nitrogen.
You must still provide a complete discussion if you make a drawing.