49.1 Some scientists call the time in which we are living the Anthropocene Period to reflect our significant impact on the planet.
The human population recently passed the 7-
The ecological footprint is the amount of land required to support an individual at an average standard of living. page 1072
Our ecological footprint reflects all the activities that support our daily life, from growing and transporting the foods that we eat to supplying the materials and energy for our homes and the vehicles that provide our transportations. page 1072
49.2 Humans have a major impact on the carbon cycle, primarily through the burning of fossil fuels, which returns carbon dioxide to the atmosphere.
Carbon dioxide is a greenhouse gas, trapping heat and thereby keeping the surface of Earth warm. page 1074
Greenhouse gases play an important role in maintaining temperatures on Earth compatible with life, but increasing levels of greenhouse gases are resulting in higher mean surface temperatures. page 1074
Changing climate has already affected the distribution of species and the composition of communities, and will continue to do so in the 21st century. page 1076
Increasing levels of CO2 are increasing the temperature and decreasing the pH of the oceans, affecting marine organisms, including corals. page 1077
We can reduce CO2 emissions, conserve finite natural resources, and contain the cost of energy by developing energy sources other than fossil fuels and improving energy efficiency. page 1080
49.3 Humans have an important impact on the nitrogen and phosphorus cycles, primarily through the use of fertilizer in agriculture.
Humans add large amounts of industrially fixed nitrogen to the environment, which enters the biosphere as fertilizer to increase food production. page 1082
Only a small percentage of fixed nitrogen is taken up by crops; the rest is returned to the atmosphere by soil microorganisms or ends up in lakes and oceans, where it results in eutrophication, a boost in primary production that depletes oxygen and can lead to the death of fish and other aquatic organisms. page 1082
A second major nutrient in fertilizer is phosphorus, which is mined rather than produced industrially. The finite supply of phosphorus raises questions about our ability to maintain agricultural production in the future. page 1082
We have increased agricultural yields through the use of fertilizer, high-
To feed a growing population, we can devote more land to agriculture or increase productivity further, but each option brings with it costs. page 1083
49.4 The impact of humans on the environment is changing the setting in which evolution acts.
Humans have altered the landscape in dramatic ways, leading to the expansion of some species, like corn and wheat, and the decrease and extinction of others. page 1084
Habitat degradation and loss may cause extinction in some of Earth’s most diverse ecosystems, such as tropical rain forests. page 1084
Overexploitation of species by hunting, fishing, and logging, threatens exploited species and could change the ecology of ecosystems where these species live. page 1085
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Invasive species, spread by human activity, are major players in biodiversity loss. page 1088
The use of antibiotics is one of the success stories of twentieth-
Amphibian populations have declined dramatically because of a combination of habitat loss, pesticide use, and the spread of infection. page 1090
49.5 Conservation biology aims to safeguard biodiversity for future generations
Reserves provide strong defense against habitat loss, overexploitation, and invasive species. page 1091
Corridors that allow species to move between reserves strengthen conservation and will be particularly important as global change affects reserves. page 1092
Sustainable development strives to match the rate at which we use resources to the rate at which they can be replenished. page 1093
49.6 In the 21st century, biologists, doctors, engineers, teachers, and informed citizens have vital roles to play in understanding our changing planet and making wise choices for our future.
Human impact can be positive as well as negative. page 1094
Describe what is meant by the term “ecological footprint.”
An individual’s “ecological footprint” is represented as the amount of land (generally given in hectares) needed to supply all the resources and energy that person uses. Consider your favorite actor. His ecological footprint would take into account all the land (or water) needed to: (1) provide the electricity to power all the lights and appliances in his house(s); (2) produce the oil or gas needed to heat his home(s) and run his car or jet; (3) cultivate the crops that provide his favorite fruits and vegetables, and grow the fish used in his favorite sushi roll; and (4) provide the cotton that is used to make his shirts. Depending on who your favorite actor is, he may have a very large ecological footprint!
Name three sources of atmospheric CO2.
Carbon dioxide can be introduced into the atmosphere by both natural and man-
Explain the relationship between atmospheric CO2 levels and mean temperature.
Carbon dioxide is a greenhouse gas that is normally present in Earth’s atmosphere. This gas absorbs solar radiation reflected off Earth’s surface and re-
Provide evidence that indicates that human activities are responsible for increases in atmospheric CO2 over the last century.
Recall from Chapter 25 that different materials (such as forest vegetation or the oil used to heat a house) are composed of three primary carbon isotopes (12C, 13C, and 14C). These isotopes are present in distinct ratios depending on the source; some sources have lots of 12C but little 14C. When these materials are burned (or used in other processes), they can generate CO2 composed of different carbon isotopes. As scientists (remember Hans Suess?) studied atmospheric CO2 levels, they determined that not only was more CO2 present in the atmosphere, the isotopic composition of this CO2 had changed. When researchers compared previous and modern measurements, they realized that the level of 14C in the atmosphere had decreased, as had the ratio of 13C to 12C. What sources could have produced the amounts of 12C, 13C, and 14C now present in the atmosphere? The answer was fossil fuels. Thus, scientists concluded that humans are, in fact, contributing to increased CO2 through industrial practices.
Describe the two ways organisms can respond to changes in CO2 levels and temperatures.
CO2-induced changes in temperature (both in the atmosphere and in the ocean) and ocean acidity can have serious consequences for many organisms. Some organisms can respond to temperature changes while remaining in the same environment; often, these organisms have to modify their behavior (i.e., like plants changing their flowering times). However, other organisms are forced to migrate to more suitable climates. For example, recall that corals require symbiotic algae for survival. As sea temperature rises, these algae migrate (presumably to waters with more favorable temperatures); however, the corals can’t migrate with the algae, as they build skeletons and are anchored to a particular location. Without the algae, the corals die. Interestingly, corals are also susceptible to CO2-induced changes in ocean acidity. As the seas become more acidic (the result of increased aquatic CO2 levels), corals can’t construct their unique skeletons and eventually die.
Describe several possible solutions to the problem of increased atmospheric CO2.
Although excess CO2 in the atmosphere is a serious problem, several steps can be taken to reduce our contribution to greenhouse gases. Efforts are being made to both remove CO2 from the environment and to limit our CO2 output. Remember that trees naturally use CO2 during photosynthesis. Thus, planting more trees via reforestation efforts helps to remove excess CO2 already in the atmosphere. The use of alternative energy sources such as wind power also means that less fossil fuels (one of the main sources of human-
Describe the causes and consequences of eutrophication.
To increase crop yields, farmers often treat their land with nitrogen or phosphate-
Describe several possible solutions to the problem of feeding a growing human population.
Increasing crop yields is one way to assure that a growing global population can be fed. This can be accomplished through devoting more land to agriculture and utilizing fertilizer. Other solutions include genetically engineering plants that are resource-
Give three examples of species that have benefited and three examples of species that have been harmed by human activity.
Human activities can have positive or negative effects on specific species. Many invasive species, which are introduced into new environments either inadvertently (e.g., through shipping) or purposefully (e.g., as food sources), have been positively affected by human actions. Such species include the Zebra Mussel, the Kudzu plant, and Brown Tree Snake. All of these invasive species have taken root in new environments where natural predators do not necessarily exist, and where endogenous organisms are not equipped to deal with competition from these invaders. As a result, the populations of these invasive species have skyrocketed.
In contrast, many species are also negatively impacted by human activities. These include: (1) certain species of frog, whose life cycles are disrupted by the introduction of agricultural pesticides into the environment; (2) corals, which experience “bleaching” in response to changes in ocean temperature (the result of excess CO2); and (3) numerous species of tree in the rain forest, which have been negatively impacted by deforestation.
Explain why amphibians are sometimes called “canaries in a coal mine.”
Both amphibians and canaries are remarkably responsive to certain changes in their environment. Much like canaries once warned miners of excess carbon monoxide levels underground, so too can amphibians warn us about dangerous levels of pesticides in the environment. In fact, we are already beginning to see the effects of excess pesticides (such as atrazine) on the life cycles of frogs. Recall that overexposure of frogs to atrazine severely affects their ability to reproduce and/or results in deformed offspring. Such observations in frogs warned scientists that atrazine may also negatively affect human reproduction, a hypothesis confirmed by evaluating the response of human placental cells to atrazine exposure.
In what ways do habitat loss, overexploitation, and invasive species threaten biodiversity?
Theory and observation show that the number of species a habitat can support reflects the areal extent of the habitat—
How do reserves and corridors help to conserve biodiversity?
Reserves provide protected (and managed) areas in which habitat loss, overexploitation, and species invasions can be minimized or even reversed. All reserves are limited in size and so corridors that connect reserves effectively increase the size and capacity for conservation of protected areas.
What is the Red Queen hypothesis, and how does it pertain to 21st-
The Red Queen hypothesis states that the environment experienced by populations is continually changing so that populations must continue to evolve simply to maintain their position in ecosystems. The concept is relevant to 21st century biology because environments are changing at an accelerated pace.