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Module 8

Unit 2 8 9 10 11 12 13 14

Introduction to Biodiversity

As we read in the unit opening case study, biodiversity is an Learning Goals
important indicator of environmental health. Conversely, a
rapid decline of biodiversity in an ecosystem indicates that it After reading this module you should be able to
is under stress. In this module, we will examine how scien-

tists define biodiversity at different scales and how biodiver- 8-1 identify how biodiversity exists at different
sity at each scale affects responses to environmental stressors. scales.
We will then examine how we can quantify biodiversity by

considering both the number of species in an area as well as 8-2 explain how biodiversity affects responses to
how evenly distributed individuals are among the different environmental stressors.
species. Finally, we will explore the challenging question of 8-3 describe how we can calculate biodiversity.

how many species currently live on Earth.

8-4 describe how we estimate the number of

species living on Earth.
8-1 How does biodiversity exist at different
scales?
Biodiversity exists from genes to population can still retain a low amount of genetic diver-
sity. For instance, the cheetah ( Acinonyx jubatus ) is a pred-
ecosystems atory cat that once roamed across much of Africa and the
Middle East. Researchers who have examined the amount
As illustrated in FIGURE 8.1 biodiversity exists on four scales: of genetic variation in existing cheetahs have discov-
,

genetic, species, habitat, and ecosystem. Each level of bio- ered that around 10,000 years ago the cheetah population
diversity is an important indicator of environmental health experienced a population bottleneck for reasons that are
and quality. unknown. When this bottleneck occurred, only a small per-
centage of the population survived and it could only carry
Genetic Diversity a small amount of the population’s original genetic varia-
tion. As a result, the population of cheetahs that exists today
Genetic diversity is a measure of the genetic variation continues to have low genetic variation. In the next section,
among individuals in a population. Large populations gen- we will explore the consequences.
erally have a high amount of variation in their genetic com-
position and this can occur for a variety of reasons that we Species Diversity
.
discuss in detail in Module 13 For example, the white-tailed
deer ( Odocoileus virginianus ) lives throughout much of North A species, as we learned in Module 0 is a group of organ-
,
America, Central America, and into northern South America. isms that is distinct from other groups in morphology (body
Across this wide geographic range, the deer live in different form and structure), behavior, or biochemical properties.
habitats, including fields, forests, and swamps. As a result, deer Individuals of the same species can breed and produce
herds living in colder climates have evolved relatively large
bodies to help conserve heat, while other herds, such as those
living in the warm climate of Florida, have evolved to have

much smaller bodies that more readily lose heat. Genetic diversity A measure of the genetic variation among
If a large population declines in number, the amount individuals in a population.

of genetic diversity carried by the surviving individu- Population bottleneck When a large population declines
als is greatly reduced, which is known as a population in number, the amount of genetic diversity carried by the
.
bottleneck If the population subsequently rebounds, that surviving individuals is greatly reduced.
ModUle 8 ■ Introduction to Biodiversity 97
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