Environmental Engineering Reference
In-Depth Information
Habitat
loss
Overfishing
Pollution
Commercial
hunting and poaching
Habitat degradation
and fragmentation
Climate change
Introducing
nonnative species
Sale of exotic pets
and decorative plants
Predator and pest control
Secondary Causes
Figure 9-7
Natural capital
degradation:
underlying and
direct causes of depletion and pre-
mature extinction of wild species.
The two major secondary causes
of wildlife depletion and premature
extinction are the loss or fragmen-
tation and degradation of habitat,
and the deliberate or accidental in-
troduction of harmful nonnative
species into ecosystems.
• Population growth
• Rising resource use
• No environmental
accounting
• Poverty
Basic Causes
of wild species. Conservation biologists sometimes
summarize the main secondary factors leading to pre-
mature extinction using the acronym
HIPPO: H
abitat
destruction and fragmentation,
I
nvasive (alien) spe-
cies,
P
opulation growth (too many people consuming
too many resources),
P
ollution, and
O
verharvesting.
According to biodiversity researchers, the greatest
threat to wild species is habitat loss (Figure 9-8), degra-
dation, and fragmentation. Many species have a hard
time surviving when we take over their ecological
“house” and their food supplies and make them
homeless.
Deforestation of tropical forests is the greatest
eliminator of species, followed by the destruction of
coral reefs and wetlands, plowing of grasslands, and
pollution of streams, lakes, and oceans. Globally, tem-
perate biomes have been affected more by habitat loss
and degradation than have tropical biomes because of
widespread development in temperate countries over
the past 200 years. Development is currently shifting
to many tropical biomes.
Island species—many of them
endemic species
found nowhere else on earth—are especially vulnera-
ble to extinction when their habitats are destroyed, de-
graded, or fragmented (Figure 9-9, p. 192). Any habitat
surrounded by a different one can be viewed as a
habi-
tat island
for most of the species that live there. Most
national parks and other protected areas are habitat is-
lands, many of them encircled by potentially damag-
ing logging, mining, energy extraction, and industrial
activities. Freshwater lakes are also habitat islands that
are especially vulnerable to the introduction of nonna-
tive species and pollution.
Science: Habitat Fragmentation
Species are more vulnerable to extinction when their
habitats are divided into smaller, more isolated
patches.
Habitat fragmentation
occurs when a large, continuous
area of habitat is reduced in area and divided into
smaller, more scattered, and isolated patches or “habi-
tat islands.” This process divides populations of a
species into smaller and more isolated groups that are
more vulnerable to predators, competitive species, dis-
ease, and catastrophic events such as a storm or fire.
Also, it creates barriers that limit the abilities of some
species to disperse and colonize new areas, get enough
to eat, and find mates.
See how serious the habitat fragmentation problem is for
elephants, tigers, and rhinos at Environmental ScienceNow.
Science Case Study: A Disturbing Message
from the Birds
Human activities are causing serious declines in the
populations of many bird species.
Approximately 70% of the world's 9,800 known bird
species are declining in numbers, and roughly one of
every six bird species is threatened with extinction,
