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Converting Between Hectares Preparing for the AP Exam
and Acres

Some measures of biodiversity are given in terms of land area, so becoming familiar with measurements of land area is important to
understanding them. In the United States we measure land area in terms of square miles or acres. A square mile is an area that is
640 acres and one acre is an area approximately 64 m by 64 m (209 feet by 209 feet). However, the rest of the world measures land
in hectares (ha), which is an area 100 m by 100 m. There are 2.47 acres in 1 ha. The conversion from hectares is relatively easy to do
without a calculator if we round to two significant figures, which gives us 2.5 acres in 1 ha.
If a nature preserve is 100 ha, what is its size in acres?
100 ha × 2.5 acres = 250 acres

YOUR A particular forest is 10,000 acres. Determine its size in hectares.
TURN

8-2 How does biodiversity affect responses to that over the past century the number of genetically distinct
varieties of important domesticated plant and animal species
environmental stressors? have been rapidly declining as farmers focus on a small num-
ber of highly productive varieties. For example, apples origi-
Increased biodiversity improves how nated as a wild plant in Kazakhstan and the original varieties
populations and ecosystems respond to have been bred into thousands of different varieties. In 1900,
U.S. farmers grew 8,000 varieties of apples, but today more
environmental stressors than 95% of these varieties are extinct ( FIGURE 8.3 ).

The various scales of biodiversity impact how populations Consequences of Habitat Diversity for
and ecosystems respond to biotic or abiotic environmental
stressors. In this section we will explore how genetic diver- Specialist and Generalist Species
sity, species diversity, and habitat diversity provide benefits to When a region contains a high diversity of habitats, there
populations and ecosystems. is an increase in the total number of species. This is because

Consequences of Genetic Diversity
High genetic diversity benefits the long-term persistence
of populations because they are better able to respond to
environmental change compared to populations with lower
genetic diversity. For example, if a population of fish possesses
high genetic diversity for disease resistance, at least some indi-
viduals are likely to carry genes that allow them to survive
whatever diseases move through the population. When there
is low genetic diversity, there is an increased likelihood that
the population will decline more when exposed to a disease.
In the case of the cheetahs, which experienced a population
bottleneck 10,000 years ago, their low genetic diversity has
made them particularly susceptible to a pathogen that kills
up to 70 percent of cheetahs that are held in captivity.
Genetic diversity can also be very important in domes-
ticated animals and plants. In the case of agricultural crops,
centuries of plant breeding have produced hundreds of dif- FIGURE 8.3 Genetic diversity in domesticated crops. Centu-

ferent varieties of crops such as corn, rice, and wheat. When ries of plant breeding has produced a tremendous diversity of
a new disease appears that can kill one crop variety, research- genetic varieties of domesticated animals and plants, including
ers can look to other varieties that contain unique genetics more than 8,000 genetic varieties of apples. Today, most of these
that are resistant to the new disease. As we will discuss later varieties no longer exist as farmers have focused on growing just

the most productive varieties. (simo bogdanovic/Alamy Stock Photo)
( Module 59 ), environmental scientists are very concerned
100 UNIT 2 ■ The Living World: Biodiversity
Uncorrected proofs have been used in this sample.
Copyright © Bedford, Freeman & Worth Publishers.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.

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