Essentials of Ecology

CONCEPT 9-3 193

Loss of Habitat Is the Single

Greatest Threat to Species:

Remember HIPPCO

Figure 9-10 shows the underlying and direct causes

of the endangerment and premature extinction of

wild species. Conservation biologists summarize the

most important causes of premature extinction using

the acronym HIPPCO: Habitat destruction, degrada-

tion, and fragmentation; Invasive (nonnative) species;

Population and resource use growth (too many people

consuming too many resources); Pollution; Climate

change; and Overexploitation (Concept 9-3).

According to biodiversity researchers, the great-

est threat to wild species is habitat loss (Figure 9-11,

p. 194), degradation, and fragmentation. The passenger

pigeon (Core Case Study, Figure 9-1) is only

one of many species whose extinction was

hastened by loss of habitat from forest clearing.

Deforestation in tropical areas (Figure 3-1, p. 50) is

the greatest eliminator of species, followed by the de-

struction and degradation of coral reefs and wetlands,

plowing of grasslands, and pollution of streams, lakes,

and oceans. Globally, temperate biomes have been af-

fected more by habitat loss and degradation than have

tropical biomes because of widespread economic devel-

opment in temperate countries over the past 200 years.

Such development is now shifting to many tropical

biomes.

Island species—many of them endemic species found

nowhere else on earth—are especially vulnerable to

extinction when their habitats are destroyed, degraded,

or fragmented. This is why the collection of islands that

make up the U.S. state of Hawaii are America’s “extinc-

tion capital” —with 63% of its species at risk.

Any habitat surrounded by a different one can

be viewed as a habitat island for most of the species

that live there. Most national parks and other nature

reserves are habitat islands, many of them encircled

by potentially damaging logging, mining, energy ex-

traction, and industrial activities. Freshwater lakes are

also habitat islands that are especially vulnerable to the

introduction of nonnative species and pollution.

Habitat fragmentation—by roads, logging, agricul-

ture, and urban development—occurs when a large,

9-3 How Do Humans Accelerate Species Extinction?

CONCEPT 9-3 The greatest threats to any species are (in order) loss or degradation

of its habitat, harmful invasive species, human population growth, pollution,

climate change, and overexploitation.

▲

NATURAL CAPITAL

DEGRADATION

Causes of Depletion and Premature Extinction of Wild Species

• Population growth


• Rising resource use


• Undervaluing natural capital


• Poverty

Underlying Causes

• Habitat loss


• Habitat degradation and fragmentation


• Introduction of nonnative species
  
  
  • Commercial hunting and poaching
  
  
  • Sale of exotic pets and decorative plants
  
  
  • Predator and pest control
  
  
  
  


• Pollution


• Climate change


• Overfishing

Direct Causes

Figure 9-10 Underlying and direct causes of depletion and premature extinction of wild species (Concept 9-3). The

major direct causes of wildlife depletion and premature extinction are habitat loss, degradation, and fragmentation.

This is followed by the deliberate or accidental introduction of harmful invasive (nonnative) species into ecosystems.

Question: What are two direct causes that are related to each of the underlying causes?