In this AP® Environmental Science crash course review, we will tackle what biodiversity is, what you need to know about it, and why it is important for the APES exam.
What is Biodiversity?
Biodiversity refers to the variety of life on planet Earth at all of its levels. It is used to describe the number and variety of organisms that are found within a specific region, ecosystem, or on planet Earth. It includes everything from rare and endangered species to common species you see all the time to fungi and microbes that we know very little about. It is important to specify what aspect you are thinking of when discussing biodiversity because it can be discussed in many different aspects.
Ecosystems that have high levels of biodiversity have a large number of species, complex food webs, a variety of ecological niches, increased genetic diversity, and abundant resources.
Evolution
Biodiversity is the result of evolution. Evolution can be defined as the changes in a population’s genetic composition that occurs over time. Evolution stems from a theory developed by Charles Darwin that specified not only that species evolve, but also how they evolve. Darwin specified that organisms produce similar organisms, but natural selection determines what traits are passed on to the next generation. Through the process of natural selection, only the fittest animals survive to adulthood and reproduce. The reproduction process then passes on desirable characteristics that helped these animals survive to reproductive age. If organisms have a trait that helps them successfully compete with other individuals in the population, this trait is more likely to be passed on. If enough time is given, species will change and evolve as they acquire more favorable traits and abandon less favorable traits. Variation of traits in a generation often looks like a bell shaped curve. Fewer individuals have one extreme or the other- most individuals are somewhere in the middle.
Natural selection can impact populations in several ways. Directional selection occurs when an environmental change gives advantages to a variation that occurs on one end of the bell curve. An example of this is the fact that giraffes with long necks can more easily get food. Stabilizing selection occurs when the selection process favors the average member of a population. An example of this is the color of squirrels. In most areas, the vast majority of squirrels are grey because it helps them blend in. Red, black, and white squirrels are more likely to be eaten and thus not pass on their characteristics. Disruptive selection is selection that favors the extremes of a population and not the average. Disruptive selection is different than directional selection because it favors both ends of the bell curve and not just one. A common example of this is the peppered moths. In London, most of the moths were light-colored. In industrialized areas, dark colored moths were more likely to survive, leading to a higher concentration of dark colored moths.
New species can also be created through isolation when populations become separated. Isolation can be geographic- when a geographic barrier separates a population- or reproductive- when members of a population cannot freely reproduce with all other members of the population.
Why is Biodiversity Important?
It is important because it offers many benefits to human populations, animal populations, and the environment. It provides food, drugs and medicine, products, ecological benefits, and aesthetic and cultural benefits. Over 80,000 plants are edible for humans and many varieties of animals are edible as well. Drugs and medicines are also a significant benefit of biodiversity. Around 50% of drugs and medicines come from natural products and there are significant possibilities for developing new medicines from natural sources. Products provided as a result of ecosystems include timber and other natural resources. Ecological benefits include natural pest control, soil formation, waste disposal, air and water purification, and many others.
Animals benefit from biodiversity in the form of increased food sources. A large number of plant and animal species provides options if one food source is wiped out or is otherwise reduced in number. It is also good for the environment. Many varieties of plants and animals help keep ecosystems functioning well in the event of disease, pests, climate change, and other environmental hazards.
Threats to Biodiversity
Despite the fact that biodiversity brings many benefits to humans, there are many threats to it, many of which are increased by human activities. The largest threat is habitat destruction, which is primarily a result of human activity. Deforestation, the creation of dams in waterways, and draining wetlands all contribute to habitat loss and destruction. Other threats to include pollution, excessive hunting and removal of plants and animals, and climate change.
Biodiversity on the AP® Environmental Science Exam
You will see questions dealing with biodiversity on all parts of the AP® Environmental Science exam. Biodiversity and its related topics are an important focus of the APES class and exam. Below, we will walk through a free response question from the 2013 AP® Environmental Science Exam.
Biological diversity, or biodiversity, has become a topic of great concern among conservationists. Biodiversity is often used by scientists and policy makers to help determine the health of ecosystems.
(a) Describe TWO characteristics shared by ecosystems that have high biodiversity.
(b) Identify TWO specific human activities that result in a loss of biodiversity, and explain how each activity lowers biodiversity.
(c) For each human activity you discussed in (b), propose a practical strategy (other than simply banning the activity) to reduce the loss of biodiversity.
(d) Describe ONE naturally occurring factor that could lead to a loss of biodiversity.
(e) Describe TWO ecological benefits that greater biodiversity provides.
In part (a) of this question, you can earn two points- one for each characteristic of ecosystems that have high biodiversity. You can state that ecosystems with high biodiversity have a large number of species, have greater genetic variability, or have greater amounts of natural resources. Since there are several correct answers, this part of the question can easily be answered even if you don’t remember all of the features of an ecosystem with high biodiversity.
Part (b) of this question also offers two points. One for each human activity and its corresponding explanation. If you leave an incorrect or incomplete explanation, you will not receive full points. Since there are also many correct answers to this part of the question, you have options. You might cite the use of monoculture farming techniques and the fact that they eliminate native species and decrease genetic variation. You might also cite overhunting, which harms biodiversity by reducing keystone species.
In part (c) of this question, you need to further apply the answers you gave in part (b) for two additional points. With the examples mentioned above, possible solutions include encouraging polyculture, agroforestry, and intercropping, and regulating hunting activities or imposing quotas. In order to receive full points for this question, you need to correctly link your solutions to the activities you listed in part (b).
In part (d) of this question, you can earn one point. There are also many correct answers to this part of the question. You might cite wildfires, natural long-term climate change, or natural disasters such as hurricanes and tsunamis.
In part (e), two points are available- one for each correct ecological benefit you name. You have a lot of options here as well, which is particularly helpful if you cannot remember all the ecological benefits of biodiversity. Correct answers include pollination, control of pests, and water and air purification.
Conclusion
In this AP® Environmental Science crash course review, we have covered everything you need to know about biodiversity and helped you understand how to correctly and completely answer questions about biodiversity on the APES exam. By carefully reviewing this information for the APES exam, you set yourself up to approach the AP® exam with confidence.
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