Receding glacier allowed primary succession to take place
Receding glacier left an area with rocks and gravel that lack the usable nitrogen essential to plant and animal life
Pioneer species like lichens, mosses, fireweed, willows, cottonwood, and Dryas.
Dryas crowd out the other plants and take over.
After about 10 years, alder seeds take root.
Alder roots have nitrogen-fixing nodules, so they are able to grow more rapidly than Dryas.
About 30 years, dense thickets of alder, willow, and cottonwood shade and kill the Dryas.
In about 80 years, Sitka spruce invades the thickets, and the alders die out since the spruce blocks the sunlight.
Finally, Hemlocks grow and establish a stable ecosystem with the spruce.
Energy Flow in Ecosystems
Movement of Energy Through Ecosystems
Everything that organisms do in ecosystems requires energy.
The flow of energy is the most important factor that controls what kinds of organisms live in an ecosystem and how many organisms the ecosystem can support.
Primary Energy Source
Most life on Earth depends on photosynthetic organisms, which capture some of the sun’s light energy and store it as chemical energy in organic molecules (food).
Primary productivity: the total amount of organic material that the autotrophic organisms of an ecosystem produce
Primary productivity determines the amount of energy available in an ecosystem.
Organisms that first capture energy, producers, include plants, some kinds of bacteria, and algae
Producer : an organism that can make organic molecules from inorganic molecules; a photosynthetic or chemosynthetic autotroph that serves as the basic food source in an ecosystem
All other organisms in an ecosystem are consumers.
Consumers: an organism that eats other organisms or organic matter instead of producing its own nutrients or obtaining nutrients from inorganic sources.
In order to study how energy moves through an ecosystem, organisms are placed in into trophic levels.
Trophic level : One of the steps in a food chain or food pyramid
Energy moves from one trophic level to another
The sun is the ultimate source of energy.
Food chain : the pathway of energy transfer through various stages as a result of the feeding patterns of a series of organisms
The lowest trophic level (first level) for any ecosystem is occupied by producers (algae, bacteria, plants).
Producers use the energy of the sun to build energy-rich carbohydrates, as well as absorb nitrogen and other key substances.
First trophic level-producers
At the second trophic level are herbivores.
Herbivores : an organism that eats only plants
Herbivores eat the primary producers so they are also known as the primary consumers.
A herbivore must be able to break down a plant’s molecules into usable compounds.
Second trophic Level-herbivores
Most herbivores rely on microorganisms, such as bacteria and protists, in their gut to help them digest cellulose.
Example: cow and horse
Humans cannot digest cellulose because they lack these special microorganisms.
At the third trophic level are secondary consumers (animals that eat other animals).
Carnivores : an animal that eats other animals
Some animals are both herbivores and carnivores; they are called omnivores
They use the simple sugars and starches stored in plants as food, but they cannot digest cellulose.
Third trophic level - Carnivore
There is a special class of consumers called detritivores, which include worms, fungal, and bacterial decomposers.
Detritivores: a consumer that feeds on dead plants and animals at all trophic levels
Bacteria and fungi are known as decomposer because they cause decay.
Decomposer: an organism that feeds by breaking down organic matter from dead organisms
Decomposition of bodies and wastes releases nutrients back into the environment to be recycled by other organisms.
The fourth trophic level is composed of tertiary consumers (carnivores that consume other carnivores)
Energy does not follow simple straight paths because individual animals often feed at several trophic levels.
Food web : a diagram that shows the feeding relationships between organisms in an ecosystem
Loss of Energy in a Food Chain
Organisms acquire energy from their environment.
The energy that organisms obtain help aid their cellular processes.
Much of the energy obtained is dispersed into the environment as heat.
During every transfer of energy within an ecosystem, energy is lost as heat.
The amount of useful energy available to do work decreases as energy passes through an ecosystem.
The loss of useful energy limits the number of trophic levels an ecosystem can support.
At each trophic level, the energy stored by the organisms in a level is about one-tenth of that stored by the organisms in the level below.
The Pyramid of Energy
The flow of energy through ecosystems is illustrated with an energy pyramid .
Energy pyramid: a triangular diagram that shows an ecosystem’s loss of energy, which results as energy passes through the ecosystem’s food chain
Each trophic level is represented by a block.
The width of each block is determined by the amount of energy stored in the organisms at that trophic level.
Limitations of Trophic Levels
The number of trophic levels that can be maintained in a community is limited by the dispersal of potential energy.
The number of individuals in a trophic level may not be an accurate indicator of the amount of energy in that level.
In order to determine the amount of energy present in trophic levels, ecologist measure biomass .
Biomass: organic matter that can be a source of energy; the total mass of the organisms in a given area
Cycling of Materials in Ecosystems
All materials that cycle through living organism are important in maintaining the health of ecosystems.
Four substances that are important in this process are: Water, carbon, nitrogen, and phosphorus.
All organisms require carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur in relatively large quantities.
The paths of water, carbon, nitrogen, and phosphorus pass from the nonliving environment to living organisms, and then back to the nonliving environment.
These paths form closed circles, or cycles, called biogeochemical cycles.
Biogeochemical cycles: the circulation of substances through living organisms from or to the environment
The Water Cycle
Of all the nonliving components of an ecosystem, water has the greatest influence on the ecosystems inhabitants.
In the nonliving portion of the water cycle, water vapor in the atmosphere condenses and falls on the Earth’s surface as rain or snow.
Some of this water seeps into the soil and becomes part of the ground water (water that is beneath the Earth’s surface)
The remaining water on the Earth’s surface is heated by the sun and reenters the atmosphere by evaporation.
In the living portion of the water cycle, much water is taken up by the roots of plants.
After passing through a plant, the water moves into the atmosphere by evaporating from the leaves, a process called transpiration.
Transpiration is also a sun-driven process.
In aquatic ecosystems (lakes, rivers, and oceans), the nonliving portion of the water cycle is the most important.
In terrestrial ecosystems, the nonliving and living parts of the water cycle both play important roles.
Water Cycle Transpiration
The Carbon Cycle
Carbon also cycles between the nonliving environment and living organisms.
Carbon dioxide in the air or dissolved in water is used by photosynthesizing plants, algae, and bacteria as a raw material to build organic molecules.
Carbon atoms may return to the pool of carbon dioxide in the air and water in three ways:
Nearly all living organisms engage in cellular respiration.
They use oxygen to oxidize organic molecules during cellular respiration, and carbon dioxide is a byproduct of this reaction.
Carbon returns to the atmosphere through combustion, or burning.
The burning wood or fossil fuels (coal, oil, and natural gas) releases carbon into the atmosphere.
Marine organisms use carbon dioxide dissolved in sea water to make calcium carbonate shells.
These shells form sediments, which form limestone, and as it erodes, the carbon becomes available to other organisms.
Carbon Cycle Dissolved CO 2 in water
The Phosphorus and Nitrogen Cycles
Organisms need nitrogen and phosphorus to build proteins and nucleic acids.
Phosphorus is an essential part of both ATP and DNA.
Phosphorus is usually present in soil and rock as calcium phosphate, which dissolves in water to form phosphate ions, PO43-.
This phosphate is absorbed by the roots of plants and used to build organic molecules
The atmosphere is about 78 percent nitrogen gas, N2, which is not usable by organisms.
The two nitrogen atoms in a molecule of nitrogen gas are connected by a strong triple covalent bond that is very difficult to break.
Few bacteria have enzymes that can break it, and they bind nitrogen atoms to hydrogen to form ammonia, NH3.
The process of combining nitrogen with hydrogen to form ammonia is called nitrogen fixation .
Nitrogen-fixing bacteria live in the soil and are also found within swellings, or nodules, on roots of beans, alder trees, and few other kinds of plants.
There are four important stages in the nitrogen cycle:
The absorption and incorporation of nitrogen into organic compounds by plants.
The production of ammonia by bacteria during the decay of organic matter.
Production of nitrate from ammonia.
The conversion of nitrate to nitrogen gas.
The growth of plants in ecosystems is often limited by the availability of nitrate and ammonia in the soil.
Today, most of the ammonia and nitrate that farmers add to soil is produced chemically in factories, rather than by bacterial nitrogen fixation.
Reminder: TEST MONDAY
Common Use of Scarce Resources and Competition
When two species use the same resource, they participate in a biological interaction called competition .
Competition: the relationship between species that attempt to use the same limited resource
Resources for which species compete include food, nesting sites, living space, light, mineral nutrients, and water.
Video: Giant Octopus Battles Shark
The functional role of a particular species in an ecosystem is called its niche .
Niche : the position (way of life) of a species in an ecosystem in terms of the physical characteristics (such as size, location, temperature, and pH) of the area where the species lives and the function of the species in the biological community.
Video: Humpback Whales' Feeding Frenzy
A niche may be described in terms of space utilization, food consumption, temperature range, requirements for moisture or mating, and other factors.
A niche is not a habitat (a location), it’s a pattern of living.
Example: Jaguar’s Niche
Diet : feed on mammals, fish, and turtles
Reproduction : Give birth from June to August, during rainy season
Time of Activity : Hunt by day and by night
A niche is often described in terms of how the organism affects energy flow within the ecosystem in which it lives.
The niches of some organisms overlap and if the resources that these resources share are in short supply, it is likely that there will be competition between organisms.
Size of a Specie’s Niche
The entire range of resource opportunities an organism is potentially able to occupy within an ecosystem is its fundamental niche .
Fundamental niche : the largest ecological niche where an organism or species can live without competition
Example: Cape May warbler (small insect-eating song bird)
Finds food in spruce tree
Eats small insects
Searches for food high on the spruce trees
Dividing Resources Among Species
The part of its fundamental niche that a species occupies is called its realized niche .
Realized niche : the range of resources that a species uses, the conditions that the species can tolerate, and the functional roles that the species plays as a result of competition in the specie’s fundamental niche
The realized niche is only a small portion of its fundamental niche which reduces competition among species.
Example: five warbler species feeds on insects in a different portion of the same tree
Competition and Limitations of Resource Use
Competition can limit how species use resources
Example: 1960’s Experiment done by Joseph Connell
Joseph worked with barnacles (marine animals that attach themselves to rocks)
Connell studied two species of barnacles that grow on the same rocks along the coast of Scotland.
Chthamalus stellatus , lives in shallow water, where it is often exposed to air by receding tides
Semibalanus balanoides , lives lower down on the rocks, where it is rarely exposed to the atmosphere.
Connell removed Semibalanus from the deeper zone, and the Chthamalus was easily able to occupy the vacant surfaces.
When the Semibalanus was reintroduced, it outcompeted Chthamalus by crowding if off the rocks.
In contrast, Semibalanus could not survive when placed in the shallow water.
The realized niche of Chthalamus is smaller than its fundamental niche because of competition from the faster-growing Semibalabus .
Competition Without Division of Resources
G. F. Gause looked at competition between similar species.
Gauses experiment showed that the outcome of competition depends on the degree of similarity between the fundamental niches of the competing species.
Gause hypothesized that if two species are competing, the species that uses the resource more efficiently will eventually eliminate the other.
This elimination of competing species is referred to as competitive exclusion .
Competitive exclusion: the exclusion of one species by another due to competition
Experiment: Gause Experiment I
Grew two species of Paramecium in the same culture tubes, where they had to compete for the same food.
The smaller of the two species, which was more resistant to bacterial waste products, drove the larger one to extinction
Gause’s Experiment I
When can Competitors Coexist?
When species avoid competition, they may coexist.
Example: Gause Experiment II
Placed P.caudatum and P.bursaria in the same culture tubes, where they had to compete for the same food.
Instead of one species winning the competition, both species survived
P. caudatum was found in the upper part of the culture tube were they feed on bacteria
P.bursaria on the other hand were found in the bottom of the culture tube were they feed on yeast
The fundamental niche of each species was the whole culture tube, but the realized niche of each species was only a portion of the tube.
Therefore, when two species used different resources, both were able to survive.
Gause’s Experiment II
Predation and Competition
Many studies have shown that predation reduces the effects of competition.
Because predation can reduce competition, it can also promote biodiversity (the variety of living organisms present in a community)
Biodiversity is a measure of both the number of different species in a community (species richness) and the relative numbers of each of the species (species diversity)
Example: Paine’s Experiment
Paine examined how sea stars affect the numbers and types of species within marine intertidal communities.
Sea stars are fierce predators of clams and mussels.
When the sea stars were eliminate, Paine noticed that the sea stars prey species fell from 15 to 8.
Paine noticed that the mussels were taking over
By preying on mussels, sea stars keep the mussel populations too low to drive out other species.
Biodiversity and Productivity
More biodiversity leads to more productivity.
Example: Tilman’s experiment
Tended 207 experimental plots in Minnesota
Each plot contained a mix of up to 24 native prairie plant species
They measure how much growth was occurring
The greater number of species a plot had, the greater the amount of plant material produced in that plot.
Plots with greater number of species also recovered more fully after a disaster.
The Atmosphere and Ecosystems
Human –induced environmental changes area affecting ecosystems worldwide and may lead to global change.
Coal-burning power plants send smoke high into atmosphere through tall smokestacks.
This smoke contains high concentrations of sulfur because the coal that the plant burns is rich in sulfur.
Scientists have discovered that the sulfur introduced into the atmosphere by smokestacks can combine with water vapor to produce sulfuric acid.
Rain and snow carry the sulfuric acid back to the Earth’s surface.
This acidified precipitation is called acid rain .
Acid Rain : precipitation that has a pH below normal and has an unusually high concentration of sulfuric or nitric acids, often as a result of chemical pollution of the air from sources such as automobiles exhaust and the burning of fossil fuels
In North America, acid rain is most severe in the northeastern United States and in southeastern Canada, areas that are downwind from coal-burning plants in the Midwest.
In the northeastern United States, rain and snow have an average pH of about 4.0 – 4.5 (water pH is 7.0)
Rainwater and some soils are naturally slightly acidic.
The acidity added by human activity is having a dramatic effect.
In the United States and Canada, thousands of lakes are “dying” as their pH levels fall below 5.0
Forests in the eastern United States and southern Canada are being damaged because the acid pH may be harming symbiotic fungi in their roots.
The Ozone Layer
The ozone layer is a protective shield against the sun’s damaging rays.
The ozone layer is being reduced, and human activity may play a large role in its reduction.
The Ozone Hole
In 1985, a researcher in Antarctica noticed that ozone levels in the atmosphere seemed to be as much as 35 percent lower than the average values during 1960s.
Satellite images taken over the South Pole revealed that the ozone concentration was unexpectedly lower over the Antarctica than elsewhere in the Earth’s atmosphere (ozone hole).
Ozone Layer and Ozone Hole
Scientist found that the disintegration of the Earth’s ozone shield was evident as far back as 1978.
Every year since then, more ozone has disappeared, and the ozone hole has grown larger, plus a smaller hole has appeared over the Artic.
The decrease in ozone allows more ultraviolet radiation to reach Earth’s surface that scientist expect an increased incidence of diseases caused by exposure to ultraviolet radiation.
These diseases include skin cancer, cataracts, and cancer of the retina.
Skin cancer, Cataracts, Cancer of the Retina
What is Destroying Ozone?
The major cause of ozone destruction is a class of chemicals called chlorofluorocarbons (CFCs) .
Chlorofluorocarbons: hydrocarbon in which some or all of the hydrogen atoms are replaced by chlorine and fluorine; used in coolants for refrigerators and air conditioners and in cleaning solvents; their use is restricted because they destroy the ozone layer
CFCs were invented in the 1920s because were considered extremely stable, supposedly harmless, and a nearly ideal heat exchanger.
By 1985, the scientific community had learned that CFCs are the primary cause of the ozone hole.
High in the atmosphere, ultraviolet radiation from the sun is able to break the usually stable bonds in CFCs.
The resulting free chlorine atoms then enter into a series of reactions that destroy ozone.
As a result of this discovery, CFCs have been banned as aerosol propellants in spray cans in the United States.
The average global temperature has been steadily increasing for more than a century, particularly since the 1950s.
In the Earth’s long history there have been many such periods of global warming , often followed by centuries of cold.
Scientist hypothesize that sunspot cycles may contribute to these cyclical changes in global temperature, but many scientists suspect that human activity may be significantly contributing to global warming.
The Greenhouse Effect
Greenhouse gases, such as water vapor, carbon dioxide, methane, and nitrous oxide, prevent the Earth from being cold as the moon.
The chemical bonds in carbon dioxide (CO 2 ) molecules absorb solar energy as heat radiates from Earth.
This process, called the greenhouse effect , traps heat within the atmosphere.
Greenhouse effect : the warming of the surface of Earth and the lower atmosphere as a result of carbon dioxide and water vapor, which absorb and reradiate infrared radiation.
There has been a large increase in carbon dioxide in the Earth’s atmosphere which can be related to the burning of fossil fuels.
Is Global Warming Occurring?
The correlation of increasing temperature with increasing carbon dioxide levels is very close.
Therefore many scientists are convinced temperature and carbon dioxide levels are related.
Both global temperature and levels of greenhouse gases may be changing because of other variables that have not been recognized yet.
Effects on Ecosystem
Effects of Chemical Pollution
One important urban environmental problem is chemical pollution.
People assumed that the environment can absorb any amount of pollution.
Lake Erie and other large lakes became polluted because of the assumption that they could absorb unlimited amounts of industrial chemicals.
Small oil spills and leaks receive little or no publicity account for more than 90 percent of all pollution.
Many of the most disastrous incidents of pollution involve industrial chemicals that are toxic or carcinogenic (cancer-causing)
Until recently, there has been relatively little regulation of the manufacture, transportation, storage, and destruction of such chemicals.
In many countries, modern agriculture introduces large amounts of chemicals into the global ecosystem.
These chemicals include pesticides, herbicides, and fertilizers.
Industrialized countries, like United States, now attempt to carefully monitor side effects of these chemicals.
Unfortunately, large quantities of many toxic chemicals that are no longer manufactured still circulate in the ecosystem.
Pesticides are molecules of chlorinated hydrocarbons that break down slowly in the environment and accumulate in the fatty tissue of animals.
These pesticides include DDT, chlordane, lindane, and dieldrin.
As these molecules pass up through the trophic levels of food chain, they become increasingly concentrated, and this process is called biological magnification .
Biological magnification : the accumulation of increasingly large amounts of toxic substances within each successive link of the food chain.
Example: Pesticide DDT
Presence of DDT in birds causes thin, fragile eggshells, which can break during incubation.
Many predatory birds in the United States and elsewhere failed to reproduce, and their numbers dwindled.
In 1972, use of DDT was severely restricted in the United States, and the threatened bird populations slowly began to increase.
United States still manufactures these pesticides and sends them to other countries
In order for us to meet the needs of an increasingly crowded world, the use of chemicals is necessary, but we must learn to use them intelligently.
This will enable us to protect the productive capacity of the Earth.
Loss of Resources
Ecosystems are being damaged due to the consumption or destruction of resources that we can not replace.
Three kinds of nonrenewable resources are being consumed or destroyed at alarming rates: species of living things, topsoil, and ground water.
Extinction of Species
Over the last 50 years, about half of the world’s tropical rain forests have been burned to make pasture and farmland and have been cut for timber.
The problem is that as the rain forests disappear, so do their inhabitants and no one knows how many species are being lost.
To find out, scientists carefully catalogue all of the residents of one small segment of forest and then extrapolate their data.
It is estimated that we will lose up to one-fifth of the world’s species of plants and animals during the next 50 years.
The tragedy of extinction is that as species disappear, so do our chances to learn about them and their possible benefits.
Example : Rosy Periwinkle
Occurs naturally in Madagascar
Two potent anticancer drugs have been isolated from the leaves of this plant
Deforestation is threatening this species of plant
Loss of Topsoil
The United States is one of the most productive agriculture countries on Earth, largely because of its fertile soil.
The topsoil has accumulated slowly as the remains of countless animals and plants decayed.
By the time humans came to plow the land, the topsoil was more than a meter thick.
This rich topsoil cannot be replaced, and it is being lost at a rate of several centimeters each decade.
Turning over the soil to eliminate weeds, allowing animals to overgraze ranges and pastures, and practicing poor land management all permit wind and rain to remove more and more topsoil.
Since 1950, the world has lost one-third of it topsoil, primarily because of human activity.
Ground-water Pollution and Depletion
Much ground water is stored within porous rock reservoirs called aquifers .
Aquifer : a porous rock that stores and allows the flow of ground water
Water seeps into aquifers too slowly to replace the large amount of water now being withdrawn.
A very large portion of it is wasted on watering lawns, on washing cars, and through leaky and inefficient faucets and toilets.
Ground water is being polluted by irresponsible disposal of chemical wastes.
Once pollution enters the ground water, there is no effective way to remove it.
Growth of the Human Population
In the very beginning, there were 5 million people on Earth.
As agriculture produced more dependable sources of food, the human population began to grow.
By 1650, the world’s population had reached 500 million.
The average global birthrate has remained near 30 births per 1,000 people per year.
However, with the development of technology to ensure better sanitation and improved medical care, the death rate has fallen steadily.
In 2002, the estimated death rate was about 9 deaths per 1,000 people per year.
The annual worldwide increase in human population is approximately 1.3 percent.
Growth of Human Population
Worldwide Rates of Growth
The world’s population exceeded 6 billion in October 1999, and the annual increase is now about 94 million.
About 260,000 people are added to the world population each day, or about 180 every minute.
Population growth is fastest in the developing countries of Asia, Africa, and Latin America.
Population growth is the slowest in the industrialized countries of North America, Europe, Japan, and in New Zealand, and Australia.
The population growth rate in the United States is only 0.8 percent.
Population Growth Patterns
The populations of Germany and Russia are declining.
The global rate of population growth has been declining.
The United Nations projects that the world’s population will stabilize at 9.7 billion by the year 2050.
Population growth tends to be highest in countries that can least afford it.
Building a sustainable world is the most important task facing humanity’s future.
The quality of life available to your children in the new century will depend to a large extent on our success.
Solving Environmental Problems
A Worldwide Effort
Environmental problems affect all inhabitants of an ecosystem without regard to state or national boundaries.
As human activities continue to place severe stresses on the ecosystems, worldwide attention must be focused on solving these problems.
A great deal of progress has been made in reducing air and water pollution.
The number of secondary sewage treatment facilities, which remove chemicals as well as bacteria from sewage, is on the increase.
“Scrubber” is a device that reduces harmful sulfur emissions from industrial smokestacks.
Emissions of sulfur dioxide, carbon monoxide, and soot, have been cut by more than 30 percent in 10 years.
Serious attempts to address the overall problem of pollution have also brought about more fundamental changes in our society.
In the United States
Two effective approaches have been taken to reduce pollution in the United States.
The first approach has been to pass laws forbidding it, which has slowed the spread of pollution.
These laws impose strict standards for what can be released into the environment.
Catalytic converters = reduce emissions
Clean Air Act = requires scrubbers on the smokestacks
A second effective approach to reducing pollution has been to make it more expensive by placing a tax on it.
Example: gasoline tax
By adjusting the tax, the government attempts to balance the confliction demands of environmental safety and economic growth.
Such taxes, often imposed on industry in the form of “pollution permits”, are becoming increasingly common.
Solving Environmental Problems
It is easy to get discouraged when considering the world’s many serious environmental problems but each of the world’s problems are solvable.
Five Steps to Success
There are five components to successfully solve any environmental problem:
Gather information about what is happening
Predict the consequences of different types of environmental intervention
Also evaluate any negative effects associated with a plan of action.
Inform the public
Explain the problem well
Contact elected officials
Monitor to see if environmental problem is being solved.
Two Success Stores
Example: Nashua River
Nashua River was severely polluted by mills in Massachusetts
Marion Stoddart organized the Nashua River Cleanup Committee.
The citizen’s campaign contributed to the passage of the Massachusetts Clean Water Act of 1966 which banned industrial dumping in the river.
The river has largely recovered.
Example: Lake Washington
Sewage plants discharged their treated outflow into the lake.
Blue-green algae growing in the lake, this algae requires an abundance of the nutrients nitrogen and phosphorus to grow.
Bacteria decomposing the dead algae would soon deplete the lake’s oxygen and would kill all life in the lake
In 1961, Lake Washington was cleaned up
Today the Lake is healthy
Humans rely on the Earth’s ecosystems for food and all of the other materials our civilization depends on.
Although solving the world’s environmental problems will take the efforts of many people, including politicians, economists, and engineers, the issues are largely biological.
Your knowledge of ecology is the essential tool that you can contribute to the effort.
You can save energy by walking, riding a bicycle, or taking public transportation to work or school.
Newspaper, aluminum products, glass containers, and many plastic containers can be recycled.
Choices that you make in your day to day activities can benefit the environment.