Lesson 11: Environmental Awareness (2.2.1)
Humans have had a large impact on the environment, sometimes without realizing it. Many activities human perform on a daily basis have a profound impact on the earth in a negative way. Population growth, pollution, global warming, burning of fossil fuels, habitat destruction, and the introduction of nonnative species are just a few things humans have done to harm the earth.
POPULATION GROWTH
Populations are affected by their birth rate, number of organisms born, and death rate, number of organisms that die. When death rate exceeds birth rate (more organisms die than are born), the population size decreases. When death rate equals birth rate (same number of organisms die that are born), the population size remains stable. When birth rate exceeds death rate (more organisms born than die), the populations size increases. Several factors influence birth rate such improved prenatal care, better medical care and birth control. Factors that influence death rates are better nutrition, medicine, and war. Human populations remained fairly constant until the 1700-1900s when growth began to increase exponentially (doubled at a constant rate). Increase in technology and medicine allowed birth rate to exceed death rate. Figure 11.1 shows this drastic increase in the human population. It is projected that the population of the Earth will continue to increase as technology; agriculture and medicine continue to improve, as show in Figure 11.2. Notice developing countries are projected to grow much quicker than industrialized countries. As our population size increases, competition for food, water, shelter, mates, and limited resources also increases. In some areas of the world, there are “water fights” where communities of people are fighting with each other for rights over fresh water. As human populations continue to grow, and resources on earth get more limited, there is potential for resources to run low or out all together. Increased competition can lead to problems between communities of people.
IMPACT OF HUMAN ACTIVITIES
POLLUTION
Pollution is caused by waste, manufacturing, power production, and the burning of fossil fuels. It can come in the form of toxic chemicals or litter. Pollution of land and water ways threatens many species, driving some to extinction. Extinction of organisms affects the entire ecosystem because it causes a shift in the food chain and increases competition amongst living organisms for the remaining food sources. Pollution also leads to diseases in humans because of increase in toxic levels in the water ways. Humans must have water to survive, but cannot drink water that is not clean. Power production releases dirt and toxic chemicals into the atmosphere, leading to many respiratory problems such as asthma. Bigger cities, such as Los Angeles, have higher percentages of respiratory issues than smaller towns with less air pollution. In 1955 the federal government passed the Air Pollution Control Act to help regulate the amount of pollutants released into the air from factories and human activities. This has since been changed and amended with the most recent amendments in 1990. By lowering pollution levels across the United States, the hope is to increase human health and decrease respiratory issues in humans. Figure 11.3 shows air pollution in a large city while Figure 11.4 shows water pollution in a waterway. The federal government is working with other countries to help reduce pollution by the use of clean energy. Using clean energy can help reduce acid rain which is created when chemicals released from industries combine with water in the atmosphere, lowering pH of the rain. Acid rain can kill plants and animals, destroy building, and cause concrete to crumble. In some areas of the mountains of North Carolina, entire forests have been killed by the effects of acid rain.
GLOBAL WARMING
Global warming is part of a natural warming process on Earth. This process is called the greenhouse effect. The greenhouse effect traps heat from the sun within the Earth’s atmosphere. Energy from the sun travels to earth and is absorbed by bodies of water, land masses, or reflected. Some of this reflected heat is released back into space, but most is trapped by atmospheric gases such as water vapor, carbon dioxide, methane (CH4), and chlorofluorocarbons (CFCs). Without the greenhouse effect, the average global temperature would be around -20°C, which is too cold for life as we know it to survive on earth. Natural processes, such as volcanoes, release large quantities of greenhouse gases, along with other gases. Volcanoes under the ocean are erupting on an almost daily basis. The gases being released eventually move through the water, up and out into the atmosphere. Volcano eruptions on land release these gases directly into the atmosphere. However, like many other natural cycles, human activities impact the earth’s natural warming cycle.
Global warming is a term used to describe the changes humans have made to the Earth’s overall climate. Activities such as burning fossil fuels release excess carbon dioxide, a greenhouse gas, into the atmosphere. Remember, natural process, such as volcanoes, also release excessive amounts of carbon dioxide into the atmosphere as well. Carbon dioxide, along with pollution and other harmful chemicals being released in the atmosphere, the potential damage being done by human activities is immeasurable. Carbon dioxide is being released into the atmosphere faster than natural processes in the carbon cycle can remove and recycle it. The average global temperature has increased by 1°C and the polar ice caps by 5°C. An increase in temperature can cause stronger reoccurring storms, ice cap melting, rise in sea levels, and increased of tidal flooding areas, to name a few. The full extent of global warming is not currently known, as we have just begun to see its effects.
Also, organisms are adapted to environments with specific temperature ranges, and if the temperature increases, it could lead to extinction of the organism in that community. Recall organisms have an impact on each other in the natural food chain process. Extinction of one or more organisms could have a profound impact on the overall ecosystem, and potentially lead to further extinction of other organisms if they are not able to adapt fast enough. Below are a few graphs and pictures to help illustrate the idea of global warming and its effects on the earth.
HABITAT DESTRUCTION
Humans need for housing, office buildings, shopping complexes, roads, crop production, and resource use have lead to the destruction of habitat on earth. Habitat destruction has had destabilizing effects on ecosystems and leading to the extinction of organisms. Deforestation, the cutting down of a forest, has eliminated many ecosystems as well. Stable ecosystems are often at or near carrying capacity for the organisms in that ecosystem. Remember, there is only a limited amount of space for organisms in each ecosystem, which is determined by the amount of available energy, food supply, number of shelters, and predator/prey interactions. For example, if a forest is cut down to build a shopping complex; many of the deer that lived in this forest may die if they cannot find a new home in a nearby forest because that new forest is already at carrying capacity for the deer. There may not be any room for additional deer. This concept applies to all organisms in the forest that was cut down. Another example of habitat destruction is the dust bowl of the 1930s. Decades of overproduction and inappropriate farming techniques stripped the fertile soil form the Great Plains in the early 1930s. Along with dust so thick it was debilitating, there was no food for primary consumers to eat and the consumers (both people and animals) were forced to move.
NONNATIVE SPECIES
Human activities have lead to the release nonnative species into ecosystems, often by accident. Nonnative species are species that are not native to a particular ecosystem. Nonnative species often have no natural predators and therefore their populations are able to grow rapidly, outcompeting native species in that environment and often leading to extinction of one or more organisms. Remember that removal of organisms in the food chain affect the entire ecosystem because of predator/prey interactions. One example of a nonnative species is the fire ant known as the red imported fire ant (RIFA). A ship bringing imported goods from South America to a port in Alabama unknowingly carried the fire ants to the United States. In the 1930s they were accidently introduced and have spread rapidly throughout much of the South and Southwestern United States; they are continuing to spread throughout the U.S. Fire ants have a venomous sting and often work together to kill small animals for food.
BIOACCUMULATION
The accumulation of chemicals in the cells and tissues of living organisms is known as bioaccumulation. As you move up the food chain, bioaccumulation affects organisms more and more. Chemicals are stored in the cells of tissues of organisms over a period of time due to the consumption of contaminated foods. Recall that because of the law of 10%, organisms higher up in the food chain must eat more in order to gain enough energy for survival. Therefore, organisms in higher trophic levels have an increased concentration of chemicals due to bioaccumulation. Farmers often spray crops with fungicides and pesticides to increase crop yield. Rain will wash some of these chemicals off, through runoff, into the waterways. Over time, the concentration of these chemicals will build up in the organisms, such as fish, living in the waterways. Bioaccumulation has almost caused the population of bald eagles to go extinct. Before the 1970’s, a chemical known as DDT was heavily used to control mosquito populations. The DDT ran off into the waterways and built up in the fish. As the bald eagles ate fish, DDT built up in their system too. This chemical caused problems with the eagle’s reproduction by causing the eggs to be very soft and unable to develop. The bald eagle population rapidly declined and came close to extinction. Figure 13.18 shows a diagram of how bioaccumulation affects organisms in an ecosystem.
RECAP: IMPACT OF HUMAN ACTIVITIES
Table 11.1 summarizes the impacts that human activities have had on the earth.
Environmental Threat / Causes of Threat / Impact of ThreatPopulation Growth / Increase in human populations. / Depleting or using up natural resources, land, and not enough food.
Pollution / Wastes, manufacturing, power production, and burning of fossil fuels. / Acid rain, ozone depletions, erosion, human diseases and respiratory problems, extinctions.
Global Warming and the Burning of Fossil Fuels / Human releasing of pollution and burning fossil fuels. / Increase in intense storms, global temperatures, sea levels, and flooding.
Habitat Destruction / Human need for housing, buildings, roads, crop production, and resource use. / Destabilizing changes in ecosystems, ecosystems crashing and extinction of organisms.
Non-native Species / Humans releasing nonnative organisms into an ecosystem intentionally or by accident. / Destabilizing changes in ecosystems, extinctions and harm to agricultural crops.
Bioaccumulation / Humans using materials made with products that have toxins. For example mercury seals from boats contaminating the water. / Destabilizing changes in ecosystems, extinctions of organisms, and the collapse of an ecosystem.
Lesson Review 11: Environmental Awareness
A. Define the following
population growth pollution global warming fossil fuels
habitat destruction nonnative species birth rate death rate
human populations exponentially pollution acid rain
global warming greenhouse effect deforestation bioaccumulation
B. Choose the best answer
1. World governments are concerned about population growth and they aggressively
encourage
A. child labor laws C. population control methods
B. industrial revamping D. agriculture techniques
2. Populations are most affected by
A. birth rates C. death rates
B. birth and death rates D. war and disease
3. The population rate minus the birth rate is
A. birth rates C. death rates
B. birth and death rates D. war and disease
4. What was the major contributing factor to the increase in human population during 1900s
A. improved medicine C. improved technology
B. improved medicine and technology D. more available food
5. Which organisms are most affected by bioaccumulation?
A. primary consumer C. third consumer (tertiary)
B. secondary consumer D. fourth consumer
6. Humans have altered the carbon cycle by
A. digging up stored nutrients and combusting them during industrial processes.
B. damming rivers and lakes
C. increasing the rate at which nitrogen is released into the environment
D. making snow caps melt
7. When human activities eradicate the top predator of an ecosystem,
A. other animals attempt to fill the niche
B. the ecosystem continues to function normally
C. humans are pleased
D. the entire ecosystem crashed and is incapable of ever recovering
8. Air pollution is being reduced through
A. automobiles having emission controls C. collecting methane produced by cattle
B. salting clouds D. slower driving speeds on roads
9. The natural warming of the Earth, but alternately described as changes humans have made to
the Earth’s overall climate
A. warming emission controls C. solar heating
B. global warming D. geothermal warming
10. Deforestation has which of the following negative effects on an ecosystem?
A. soil nutrient depletion C. destabilizing changes
B. possible extinction of organisms D. all of the above
11. In what year did energy consumption by humans really begin to show an increase?
A. 1400 C. 1800
B. 1600 D. 1900
12. What is true of non-native species when released by humans into the environment?
A. extinctions may occur C. harm to agricultural crops may occur
B. destabilizing changes in ecosystems D. all of the above
13. Which trophic level is most affected by bioaccumulation?
A. producers C. secondary consumers
B. primary consumers D. tertiary consumers
C. Complete the following exercises.
1. Explain why developing countries experience a greater increase in human population than industrial nations?
2. How does the growth in human populations affect our available resources?
3. Can you think of other ways to control human population?
4. List two ways humans contribute to global warming and one natural process that contributes to global warming.