Essentials of Ecology

(Kiana) #1

194 CHAPTER 9 Sustaining Biodiversity: The Species Approach


contiguous area of habitat is reduced in area and di-
vided into smaller, more scattered, and isolated patches,
or habitat islands. This process can decrease tree popu-
lations in forests (Science Focus, at right), block migra-
tion routes, and divide populations of a species into
smaller and more isolated groups that are more vulner-
able to predators, competitor species, disease, and cata-
strophic events such as storms and fires. Also, it creates
barriers that limit the abilities of some species to dis-
perse and colonize new areas, to get enough to eat, and
to find mates. Migrating species also face dangers from
fences, farms, paved areas, skyscrapers, and cell phone
towers.

Certain types of species are especially vulnerable to
local and regional extinction because of habitat frag-
mentation. They include species that are rare, species
that need to roam unhindered over large areas, and
species that cannot rebuild their populations because
of a low reproductive capacity. Species with special-
ized niches and species that are sought by people for
furs, food, medicines, or other uses are also especially
threatened by habitat fragmentation.
Scientists use the theory of island biogeography
(Science Focus, p. 90) to help them understand the ef-
fects of fragmentation on species extinction and to de-
velop ways to help prevent such extinction.

Range 100 years ago
Range today

Range in 1700
Range today

Probable range 1600
Range today

Former range

Range today

African Elephant Asian or Indian Elephant

Indian Tiger Black Rhino

Active Figure 9-11 Natural capital degradation: reductions in the ranges of four wildlife spe-
cies, mostly as the result of habitat loss and hunting. What will happen to these and millions of other species when
the world’s human population doubles and per capita resource consumption rises sharply in the next few decades?
See an animation based on this figure at CengageNOW. Question: Would you support expanding these ranges
even though this would reduce the land available for people to grow food and live on? Explain. (Data from Interna-
tional Union for the Conservation of Nature and World Wildlife Fund)
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