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LEARNING OBJECTIVES
People have long wondered how the amazing diversity of living things on Earth
came to be. This diversity has developed through biological evolution and is
affected by interactions among species and by the environment. After reading
this chapter, you should understand:
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How mutation, natural selection, migration, and genetic drift lead to
evolution of new species.
• Why people value biological diversity.
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How people can affect biological diversity.
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Why so many species have been able to evolve and persist.
How biological diversity may affect biological production, energy flow,
chemical cycling and other ecosystem processes.
• What environmental major problems are associated with biological diversity.
The concepts of the ecological niche and habitat.
Summary
• Biological evolution—the change in inherited characteristics of a
population from generation to generation—is responsible for the
development of the many species of life on Earth. Four processes that
lead to evolution are mutation, natural selection, migration, and
genetic drift.
• Biological diversity involves three concepts: genetic diversity (the
total number of genetic characteristics), habitat diversity (the
diversity of habitats in a given unit area), and species diversity.
Species diversity, in turn, involves three ideas: species richness
(the total number of species), species evenness (the relative
abundance of species), and species dominance (the most abundant
species).
• About 1.4 million species have been identified and named. Insects and
plants make up most of these species. With further explorations,
especially in tropical areas, the number of identified species,
especially of invertebrates and plants, will increase.
• Species engage in three basic kinds of interactions: competition,
symbiosis, and predation–parasitism. Each type of interaction affects
evolution, the persistence of species, and the overall diversity of
life. It is important to understand that organisms have evolved
together so that predator, parasite, prey, competitor, and symbiont
have adjusted to one another. Human interventions frequently upset
these adjustments.
• The competitive exclusion principle states that two species that have
exactly the same requirements cannot coexist in exactly the same
habitat; one must win. The reason that more species do not die out
from competition is that they have developed a particular niche and
thus avoid competition.
• The number of species in a given habitat is affected by many factors,
including latitude, elevation, topography, the severity of the
environment, and the diversity of the habitat. Predation and moderate
disturbances, such as fire, can actually increase the diversity of
species. The number of species also varies over time. Of course,
people affect diversity as well.