Essentials of Ecology

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)