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Biodiversity
Article by: Michelle A. Marvier, Department of Environmental Studies and Sciences, Santa Clara University, Santa Clara, California,
and Donald W. Linzey, Wytheville Community College, Wytheville, Virginia.
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The number of different plant and
animal species living in a defined
ecosystem or study area; a contrac-
tion of biological diversity. Bio-
diversity includes genetic diversity
(variability in the genetic makeup
among individuals in a single species),
species diversity (the variety of species
in different habitats on the Earth),
and ecological diversity (the variety
of biological communities that inter-
act with one another and with their
nonliving environments). Biodiversity
can be expressed mathematically as an
index that includes both the number of
different species in a particular ecosys-
tem (species richness) and the relative
abundance of each species present
(species equitability). In addition,
biodiversity across the world can be af-
fected detrimentally by human activity,
especially by human-caused habitat
loss and degradation. The biodiversity
of these regions, known as biological
hotspots (Fig. 1), is a great concern of
conservationists.
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Key Concepts
• Biological diversity, or biodiversity, is a measurement of the number of different plant and animal species living
in a particular ecosystem.
• Biodiversity has many aspects, including genetic diversity, species diversity, and ecological diversity.
• Mathematically, biodiversity is expressed as species richness and species equitability.
• The greatest biodiversity occurs in warm, wet climates, such as tropical rainforests.
• Human activities can cause rapid, dramatic decreases in biodiversity, leading to decreased ecosystem stability
in biological hotspots, and a decline in genetic protection against natural extinctions.
Fig. 1: Global biodiversity hotspots. There are more than 30 biodiversity hotspots located around the world. These areas have
experienced severe habitat losses (at least 70%) as the result of human activities, hampering the work of conservationists in
their attempts to preserve endemic species.
(Credit: Conservation International Foundation)
Global biodiversity
Most estimates of the total number of global species range from 3 to 30 million, but
some researchers indicate that this number may be greater than 100 million. Out of
the total number, though, only about 1.75 million species have been scientifically
described. The best-studied groups include plants and vertebrates (phylum Chordata),
whereas poorly described groups include fungi, nematodes, and arthropods. Species
that live in the ocean (Fig. 2) and in soils remain poorly known. Abiotic factors, such as
