The sequence of events that occur during ecological succession can be chosen.
There are two types of ecological succession.
Over time, each community's history can be surveyed.
Dynamic changes occurring during the history of Earth have influenced the distribution of life.
During the past, we have discussed how continental drift contributed to mass extinctions.
Many forms of marine life became extinct as the continents slowly came together.
When the continents moved toward the poles, glaciers drew water from the oceans and even chilled once-tropical lands.
Between ice ages, glaciers retreated, changing the environment and allowing life to colonize the land again.
Complex communities evolved over time.
Many ecologists try to observe changes as they occur.
A storm blowing down a patch of trees, a beaver damming a pond, and a volcanic eruption are just some of the disruptions that can occur in a community.
Over time, changes occur in the community.
Ecological succession involves a series of species replacements.
This type of succession occurs in areas where there is no base soil.
When a cultivated field returns to a natural state, this type of succession occurs.
As glaciers retreated from Glacier Bay, Alaska, this is an example of primary succession.
The area left vacant by the retreating glacier is invaded by Lichens and mosses.
There are bushes in the soil.
The fast-growing trees help build the soil.
Improved soil conditions allow the white spruce-Western hemlock community to develop, eventually moving toward a more mature and stable community.
The first species to start secondary succession are these.
Certain species are common to certain stages in a large conifer plantation in central New York State.
The process of regrowth is similar to the process of secondary succession from a glacier.
In 1916, F. E. Clements proposed that succession in a particular area will determine whether a desert, a type of grassland, or a particular type of forest was created.
He said that coniferous forests occur in northern latitudes, deciduous forests in temperate zones and tropical rain forests in the tropics.
He thought that soil conditions might affect the results.
Shallow, dry soil can produce a grassland where a forest is not expected, or rich soil can produce a woodland where a prairie is expected.
The invasion and replacement by organisms of the next stage was hypothesised by Clements.
Shrubs can't grow on the dunes until the soil develops.
shrubs can't arrive until grasses have made the soil suitable for them Grass-shrub-forest development occurs in a sequential way if each group of species prepares the way for the next.
The model predicts that colonists will hold on to their space and prevent the growth of other plants until they die or are damaged.
Successional stages may reflect the length of time it takes a species to mature.
The development of the grass-shrub-forest could be accounted for by this alone.
The length of time it takes for trees to grow might give the impression that there is a series of plant communities, from the simple to the complexample.
The dynamic nature of natural communities has been recognized as a community's most outstanding characteristic.
It seems obvious that the most complex communities have different stages of succession.
Community diversity is greatest if a sample of all stages is present.
Succession may not be complete anywhere on Earth, so we don't know if it continues at specific end points.
There are events that occur during succession.
An is made up of the interactions between populations and their environment.
The environment includes the atmosphere, water, and soil.
The biotic components can be categorized according to their food source.
Plants are producers.
Caterpillars and rabbits are omnivorous.
Snakes and hawks are omnivorous.
Land plants and algae are included in the autotrophs.
They have the ability to carry on photosynthesis in freshwater and marine habitats.
Most bodies of water have aquatic autotrophs that make up the phytoplankton load.
Green plants are the dominant photosynthesizers.
Some autotrophicbacteria are synthetic.
They use the energy they get from the oxidation of compounds to synthesise organic compounds.
Communities can be found in some of the caves along the deep-sea ridges where there is no sunlight.
They are called consumers because they consume food from a producer.
There are animals that eat directly on plants.
Large and small animals are both large and small in nature.
Zooplankton and various fishes are large herbivores in aquatic habitats.
The omnivores feed on both plants and animals.
omnivores include chickens, raccoons, and humans.
The carcasses of dead animals can be eaten by animals such as vultures and jackals.
Marine fan worms and burrowing clams take different forms from the water.
Some insects are called detritivores.
Decomposers release substances that plants take up again.
Plants would only be dependent on physical processes, such as the release of minerals from rocks, for their nutrition.
Energy flow and chemical cycling are two fundamental phenomena that are characterized by a diagram of all the biotic components.
The energy flow begins when producers absorb solar energy and the chemical cycling begins when producers take in the nutrition from the physical environment.
Through photosynthesis, producers make food for themselves and other people within the system.
All the energy from the sun is dissipated as heat.
There are various pathways for energy to flow through.
When an animal eats another animal, only a portion of the original amount of energy is transferred.
The energy goes into the environment as heat.
Without continual input of solar energy, the vast majority of ecosystems cannot exist.
Only a small portion of the organic nutrients made by producers is passed on to consumers.
Only a small percentage of the vitamins and minerals that lower-level consumers consume is available to higher-level consumers.
A certain amount of the food eaten by an herbivore is not absorbed and is eliminated as feces as shown in Figure 45.17 The nitrogenous waste is removed as urine.
A large portion of the assimilated energy is used during cellular respiration for the production of ATP.
The remaining energy can be used to increase body weight or offspring.
Less than 10% of the food energy taken in by an animal is passed on to another.
Defecation, excretion, and death are some of the things that a large portion goes to.
The elimination of feces and urine by a Heterotroph doesn't mean that organic resources are lost to the environment.
They represent the organic vitamins and minerals that are available to the decomposers.
Decomposers convert the organic nutrients, such as glucose, back into chemicals that can be found in the soil or atmosphere.
Producers have completed their cycle when they absorb these chemicals.
The laws of thermodynamics support the idea that energy flows through an environment.
The first law says that energy can't be created or destroyed.
This explains why organisms are dependent on a constant source of energy, usually solar energy.
The second law states that with every transformation some energy is degraded into a less available form, such as heat.
There is a 132,000 m2 forest in New Hampshire.
A food web is a diagram that shows the various paths of energy flow.
The organisms that feed on the acorns and leaf tissue will get some of the energy from the oak tree.
A portion of the energy available in the form of animals such as rabbits, deer, and mice will be transferred to other animals.
omnivores are organisms that feed on both the producers and the herbivores.
There is a food web.
Food webs describe who eats who.
There is a possible transfer of energy within a food web.
Birds are fed on nuts by a hawk.
The tree is a producer, the first series of animals are primary consumers, and the next group of animals are secondary consumers.
The green arrows show the possible transfer of energy within a detrital food web.
The organisms in the detrital food web are fed on by animals in the food web.
The detrital food web is connected to the grazing food web.
Energy is provided to soil organisms by tritus.
In turn, earthworms provide energy to other animals, such as shrews or salamanders.
The detrital and grazing food webs are connected because the members of a detrital food web may become food for aboveground carnivores.
We tend to think that trees are the largest storage of organic matter and energy, but this is not the case.
The organic matter lying on the forest floor and mixed into the soil contains more energy than the leaf matter of living trees.
The detrital food web may hold more energy than the grazing food web.
Food chains are diagrams that show a single path of energy flow.
A food web or chain has atrophic levels.
The loss of energy between trophic levels causes the food chains to be short.
Less than 10% of the energy of one trophic level is available to the next trophic level.
If a population consumes 1,000 kilograms of plant material, only about 100 kilograms are converted into the body tissue of the first- and second-level carnivores.
Few top-level carnivores can be supported in a food web because of the 10% rule.
Figure 45.19 shows the flow of energy with large losses between levels.
The detrital food web plays a significant role in bogs and there is a sharp drop in the amount of biomass between the producer and herbivore levels.
A pyramid is created by the amount of energy flowing from one trophic level to the next.
Problems arise when constructing pyramids.
There would be more herbivores than autotrophs in Figure 45.18.
The explanation has to do with size.
An autotroph can be as small as a tiny alga or as large as a beech tree, while an herbivore can be as small as a caterpillar or as large as an elephant.
The number of organisms is the main factor in determining the size of a pyramid.
The Page 865 herbivores are expected to have a greater biomass than the producers.
In some lakes and open seas where there is only one producer of algae, the herbivores may have a higher biomass than the producers.
Some ecologists are hesitant about using pyramids because of these drawbacks.
Even though a large portion of energy is thrown away, the decomposers are rarely included in pyramids.
The four main biogeochemical cycles are water, carbon, phosphorus, and nitrogen.
A biogeochemical cycle can be either gaseous or sedimentary.
The chemical is absorbed from the soil by the plant roots and then returned to the soil by the decomposers.
The carbon and nitrogen cycles are gaseous, meaning that the chemical is withdrawn from the atmosphere as a gas.
The components of the ecosystems are shown in Figure 45.20.
Fossil fuels, minerals in rocks, and oceans are normally unavailable sources, but exchange pools, such as those in the atmosphere, soil, and water, are available sources of chemicals for the biotic community.
Pollution can be caused when human activities remove chemicals from the water and make them available to the biotic community.
Human activities cause pollution because they upset the normal balance of nutrients for producers in the environment.
The transfer rate of water is indicated by the width of the arrows.
Evaporation from the ocean exceeds precipitation, so there is a net movement of water vapor onto land, where precipitation results in surface water and groundwater, which flow back to the sea.
Fresh water is first distilled from salt water.
The salts are left behind when fresh water is lost due to the sun's rays.
A gas is converted into a liquid during condensation.
Fresh water rises into the atmosphere, collects in the form of a cloud, cools, and falls as rain over the land.
transpiration is the process of water leaving land and entering bodies of fresh water.
All fresh water is returned to the sea when land is above sea level.
Water is contained within standing bodies, flowing bodies, and rivers.
Some of the water from precipitation makes its way into the ground and saturates the earth.
The water table is at the top of the saturation zone.
Water can be found in the rock layers of the aquifer.
Water is usually released to wells or springs.
When snow and rain accumulate in the soil, the Aquifers are recharged.
Some parts of the United States, especially the arid West and southern Florida, have withdrawals that exceed the level of recharged water.
Residents in these locations may run out of water within a few years due to the dropping of the groundwater level.
3% of the world's supply of water is fresh water.
A new supply of water is always being produced because of the water cycle.
It is possible to run out of fresh water if the rate of consumption exceeds the rate of production or if the water is polluted.
In the carbon cycle, organisms exchange carbon dioxide with the atmosphere.
The exchange pool for the carbon cycle is CO2 in the atmosphere.
Plants take up CO2 from the air.
Both autotrophs and Heterotrophs use CO2 in their nutrition.
Plants return carbon to the atmosphere as CO2.
Carbon dioxide is recycled by way of the atmosphere.
The transfer rate of carbon into the atmosphere is similar to the rate of withdrawal by plants.
The water and carbon dioxide combine to form bicarbonate ion.
The burning of fossil fuels and destruction of vegetation are placing more carbon dioxide in the atmosphere than can be withdrawn.
The exchange of CO2 with the atmosphere is indirect.
Carbon dioxide from the air is combined with water to make bicarbonate ion.
The main source of carbon is this.
When aquatic organisms respire, the CO2 they give off becomes HCO - 3.
The carbon cycle can be found in living and dead organisms.
800 billion tons of organic carbon is contained in the world's biotic components.
The remains of plants and animals are estimated to hold up to 3000 billion tons.
Fossil fuels are the materials we call coal, oil, and natural gas.
The limestone and calcium carbonate shells hold the carbonate that accumulates in carbon.
Many marine organisms have calcium carbonate shells in the ocean.
Limestone is the result of geologic forces changing the sediments into it.
The burning of fossil fuels and the destruction of forests are causing more CO2 to be released into the atmosphere.
The organisms that take up excess carbon dioxide are reduced when humans do away with forests.
The amount of CO2 released into the atmosphere is twice what can be absorbed by the producers on the planet.
The excess CO2 goes into the ocean.
Human activities emit gases into the atmosphere.
Nitrogen oxide (N2O), methane (CH4) and animal waste are included.
The global climate has warmed since the Industrial Revolution.
The figure depicts the cycle of phosphorus.
Some of these become available to plants, which usephosphate in a variety of molecule, including the nucleotides that become a part of DNA andRNA.
Animals use some of thephosphate into their teeth, bones, and shells.
The death and decay of organisms and the decomposition of animal waste will eventually makephosphate ion available to producers again.
Plants are usually limited by the amount ofphosphate that is already being used within food chains.
The size of the population is influenced by the levels ofphosphates in the environment.
When it becomes a part of the ocean, it is lost to the biotic communities.
In Page 867, there is a story about how some phosphate runs off into the aquatic environment before it can become trapped.
Producers on land don't have access tophosphate until a geologic upheaval exposes the rocks on land.
The cycle begins again.
Humans increase the supply ofphosphate by mining ores used in the production offertilizer and detergents.
Runoff of phosphate and nitrogen fromfertilizer use, animal waste from livestock feedlots, and discharge from sewage treatment plants result in overenrichment of waterways.
Plants can't make use of nitrogen in its gaseous form, which makes up about 80% of the gases in the atmosphere.
Nitrogen in the environment can limit the size of the population.
Nitrogen fixation occurs when nitrogen gas is converted to ammonia, a form plants can use.
Some free-livingbacteria in the soil can fix atmospheric nitrogen in this way.
Some nitrogen-fixingbacteria live on the roots of beans, peas, and clover.
They make organic compounds available to the plants so that they can grow.
Nitrogen is made available to biotic communities by internal cycling of the element.
Without human activities, the amount of nitrogen returned to the atmosphere exceeds the amount of nitrogen withdrawn from the atmosphere.
Plants can use nitrates as a source of nitrogen.
nitrification is the production of nitrates during the nitrogen cycle.
There are two ways in which nitrification can occur.
Cosmic radiation, meteorite trails, and lightning provide the energy needed for nitrogen to react with oxygen in the atmosphere.
NO2 is converted to NO3 with the help of 2nitrite.
Use 4 and NO3 from the soil to make nucleic acids.
Denitrification is the conversion of nitrate back to nitrogen gas.
The process of denitrifyingbacteria living in the mud of lakes and estuaries is a part of their metabolism.
Denitrification counterbalances nitrogen fixation in the nitrogen cycle.
The transfer rates in the nitrogen cycle are altered by humans.
There is an overgrowth of aquatic plants in lakes and rivers.
A massive fish kill can be caused by enlarged populations of decomposers using up all the oxygen in the water.
The water and gases combine to form acids that return to the earth.
Acid deposition has affected forests and lakes in northern Europe, Canada, and the northeastern United States.
Acid deposition can affect agricultural yields and marble, metal, and stonework.
The start of a food chain can be traced back to the base of an ecological pyramid.