Essentials of Ecology

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tially serious environmental problems, including pre-

mature extinctions.

This approach is based on the precautionary

principle: When substantial preliminary evidence in-

dicates that an activity can harm human health or the

environment, we should take precautionary measures

to prevent or reduce such harm, even if some of the

cause-and-effect relationships have not been fully es-

tablished, scientifically (Concept 9-4C). It is based on the

commonsense idea behind many adages such as “Bet-

ter safe than sorry” and “Look before you leap.”

Scientists use the precautionary principle to argue

for preservation of species, and also for preserving entire

ecosystems, which is the focus of the next two chapters.

Passenger Pigeons and Sustainability

The disappearance of the passenger pigeon (Core Case Study) in

a short time was a blatant example of the effects of activities un-

dertaken by uninformed or uncaring people. Since the passenger

pigeon became extinct, we have learned a lot about how to pro-

tect birds and other species from premature extinction resulting

from our activities. We have also learned much about the impor-

tance of wild species as key components of the earth’s biodiver-

sity and of the natural capital that supports all life and economies.

Yet, despite these efforts, there is overwhelming evidence

that we are in the midst of wiping out as many as half of the

world’s wild species within your lifetime. Ecological ignorance ac-

counts for some of the failure to deal with this problem. But to

many, the real cause of this failure is political. They would argue

that we lack the will to act on our scientific knowledge and our

ethical judgments.

In keeping with the four scientific principles of sustain-

ability (see back cover), acting to prevent the premature extinc-

tion of species helps to preserve the earth’s biodiversity and to

maintain species interactions that help control population sizes,

energy flow, and matter cycling in ecosystems. Thus it is not

only for the species that we ought to act, but also for the overall

long-term health of the biosphere on which we all depend, and

for the health and well-being of our own species. Protecting wild

species and their habitats is a way of protecting ourselves and our

descendants.

The problem is complex, and so are the solutions. Protecting

biodiversity is no longer simply a matter of passing and enforcing

endangered species laws and setting aside parks and preserves.

It will also require slowing climate change, which will affect

many species and their habitats. And it will require reducing the

size and impact of our ecological footprints (Figure 1-10, p. 15).

Although the solutions to biodiversity loss and degradation are

complex, they are well within our reach.

REVISITING

The great challenge of the twenty-first century

is to raise people everywhere to a decent standard of living

while preserving as much of the rest of life as possible.

EDWARD O. WILSON

REVIEW

1. Review the Key Questions and Concepts for this chapter
   on p. 184. What factors led to the premature extinction of
   the passenger pigeon in the United States?


2. Distinguish between background extinction and
   mass extinction. What is the extinction rate of a
   species? Describe how scientists estimate extinction
   rates. Give four reasons why many extinction experts
   believe that human activities are now causing a sixth
   mass extinction. Distinguish between endangered
   species and threatened species. List some character-
   istics that make some species especially vulnerable to
   extinction.


3. What are two reasons for trying to prevent the premature
   extinction of wild species? What is the instrumental

value of a species? List six types of instrumental values

provided by wild species. How are scientists using DNA

analysis to reduce the illegal killing of elephants? What is

theintrinsic (existence) value of a species?

4. What is biophilia? Why should we care about bats?


5. What is HIPPCO? In order, what are the six largest
   causes of premature extinction of species resulting from
   human activities? Why are island species especially vul-
   nerable to extinction? What is habitat fragmentation, and
   how does it threaten many species?


6. Describe the threats to bird species in the world and in
   the United States. List three reasons why we should be
   alarmed by the decline of bird species.