Townsend C.R., Begon M., Harper J.L. Essentials of Ecology

Подождите немного. Документ загружается.

into focus three very different ways of looking at our effects on the natural world.

First, there are the environmental outcomes – the realm of the ecologist. But there

are also economic and sociopolitical perspectives. In this section we explore this

triple bottom-line approach to sustainable natural resource use by considering

two examples – one at a regional scale (Section 13.5.1) and the other global

(Section 13.5.2).

13.5.1 Managing an agricultural landscape

When farm production becomes too intensive and widespread, biodiversity is lost

because of the loss of species-rich habitat remnants and the impact of high levels

of pesticides. At the same time there is an adverse effect on ecosystem services,

such as the provision of water of high quality for drinking and contact recreation.

Normally provided ‘free’ from a healthy landscape, these can be lost because

of the input of large quantities of nitrogen and phosphorus, ﬁne sediment from

eroding land, and an increase in water-borne pathogens from farm animals that

affect humans (such as the Giardia parasite).

The impact of agriculture depends on the proportion of the landscape that

is used for production. One small farm – even if there is excessive use of plow,

fertilizer and pesticide – will have little effect on biodiversity and water quality

in the landscape as a whole. It is the cumulative effect of larger and larger areas

of intensive agriculture that depletes the region’s biodiversity and reduces the

quality of water needed for other human activities. In other words, management

of agricultural landscapes needs to be done at a regional scale.

Santelmann et al. (2004) integrated the knowledge of experts in environ-

mental, economic and sociological disciplines into alternative visions of a particular

landscape – the catchment area of Walnut Creek, in an intensively farmed part

of Iowa, USA. They mapped the present pattern of land use and then created

three future management strategies, assessing how farm income, water quality

and biodiversity would be expected to change under each scenario. A production

scenario imagines what the catchment will look like in 25 years if continued

priority is given to corn and soybean production (‘row’ crops), following a

policy that encourages extension of cultivation to all the highly productive soils

available in the catchment. A water quality scenario envisions a new (hypothetical)

federal policy that enforces chemical standards for river and ground water,

and supports agricultural practices that reduce soil erosion. And a biodiversity

scenario assumes a new (hypothetical) federal policy to increase the abundance

and richness of native plants and animals – in this case a network of biodiversity

reserves is established with connecting habitat corridors (including the riparian

zones of rivers).

Figure 13.14 compares for the three scenarios the distribution of agricultural

and ‘natural’ habitats in 25 years’ time. Compared with the current situation,

the ‘production’ scenario produces the most homogeneous landscape, with an

increase in row crops and a decrease in the less proﬁtable pasture and forage

crops. The ‘water quality’ scenario leads to more extensive riparian strips of

natural vegetation cover and more perennial crop cover (pasture and forage

crops), which are conducive to both higher water quality and biodiversity.

Finally, the ‘biodiversity’ scenario has even wider riparian strips together with

prairie, forest and wetland reserves, and an increase in strip intercropping, a

Chapter 13 Habitat degradation

449

comparing three scenarios for

managing a catchment area

9781405156585_4_013.qxd 11/5/07 15:03 Page 449

Part IV Applied Issues in Ecology

450

Present Production

Water quality

Biodiversity

Land cover classes

Row crops

Strip intercropping

Perennial herbaceous cover

Woodland/woody cover

Water/wetland

Urban/residential/roads

Figure 13.14

Present landscape (top left) and

alternative future scenarios for the

Walnut Creek catchment area in

Iowa, USA. In comparison to the

current situation, note how row crops

increase at the expense of perennial

cover in the ‘production’ scenario.

In the ‘water quality’ scenario, note

the increase in perennial cover

(pasture and forage crops) and wider

riparian buffers. In the ‘biodiversity’

scenario, note the increase in strip

intercropping, the wide riparian

buffers and the extensive prairie,

forest and wetland restoration

reserves.

FROM SANTELMANN ET AL., 2004

farmers accept a ‘biodiversity’

scenario despite lower

productivity

farming practice that beneﬁts biodiversity because it increases connectivity between

reserves.

The percentage change after 25 years in economic, water quality and bio-

diversity terms is shown for each scenario in Figure 13.15. Not surprisingly,

the ‘biodiversity’ scenario ranks highest for improvements in plant and animal

biodiversity. More unexpected is the ﬁnding that the land use and manage-

ment practices required by the ‘biodiversity’ scenario are nearly as proﬁtable to

farmers as current practices. The ‘biodiversity’ scenario also ranks highest in terms

of acceptability to farmers (based on farmer ratings of images of land cover under

each scenario), and provides water quality improvements similar in magnitude

to those in the ‘water quality’ scenario. Despite the slightly higher proﬁtability of

the ‘production’ scenario, it seems that the farmers would not be unhappy with

a ‘biodiversity’ strategy that provides the greatest beneﬁts to the community at

large in terms of biodiversity and ecosystem services.

13.5.2 Global environmental outcomes of different

sociopolitical scenarios

Dealing with the diversity of views among neighbors in a farming region is

difﬁcult enough, but our biggest environmental problems require a multinational,

global change to the way we deal with nature.

9781405156585_4_013.qxd 11/5/07 15:03 Page 450

An analysis of four contrasting sociopolitical scenarios in Table 13.2 explores

likely trends in climate change, pollution problems and the state of ecosystem

services. If there is little change in our sociopolitical outlook – that is, if our world

remains regionalized and fragmented and mainly concerned with security and

protection – the order from strength scenario is expected to apply, with poor

economic growth, degradation of all ecosystem services and a large increase in

global temperature. A more globally connected society (global orchestration)

could produce higher economic growth and the biggest improvement for the

poorest people, but at the cost of many ecosystem services and with the largest

predicted temperature increase (particularly because of continued heavy fossil

fuel use). The scenario adapting mosaic, of a world driven by local communities

focusing on sound environmental management (such as our regional example

in Section 13.5.1) would lead to the smallest economic growth, improvements

to all ecosystem services and an intermediate rise in global temperature. Finally,

the technogarden scenario, with its environmentally sound but highly managed

ecosystems, and crucially with a climate change policy (stabilizing carbon dioxide

at 550 ppm), leads to the smallest rise in temperature, reduces nutrient pollution

of waterways and improves ecosystem services – except cultural ones, because

many ecosystems are managed and unnatural.

Which of these, or other, scenarios comes to pass depends on a wide range of

sociopolitical factors. Watch this space!

Chapter 13 Habitat degradation

451

Figure 13.15

Percent change in the Walnut Creek catchment area for each

scenario (‘production’, ‘water quality’ and ‘biodiversity’, compared

to the current situation) in water quality measures (sediment,

nitrate concentration), an economic measure (farm income in

the catchment as a whole), a measure of farmer preference for

each scenario (based on farmer ratings of images of what the land

cover would look like under each scenario) and two biodiversity

measures (plant and vertebrate). The ‘biodiversity’ and ‘water

quality’ scenarios rank above the ‘production’ scenario in all but

economic proﬁtability.

200

150

100

–50

–100

% change over 25 years

Sediment export

(tonnes yr

–1

)

Nitrate export

(kg yr

–1

)

Farm income (US$

per catchment)

Farmer

preference

Plant

biodiversity

Vertebrate

biodiversity

Production

Water quality

Biodiversity

AFTER SANTELMANN ET AL., 2004

9781405156585_4_013.qxd 11/5/07 15:03 Page 451

Part IV Applied Issues in Ecology

452

Table 13.2

Four scenarios that explore plausible futures for ecosystems and human well-being based on different assumptions about sociopolitical forces of

change and their interactions. Greenhouse gas emissions [carbon dioxide (CO

), methane (CH

), nitrous oxide (N

O) and ‘Other’] are expressed

as gigatons of carbon-equivalents (GtC-eq).

FROM TOWNSEND, 2007; BASED ON MILLENNIUM ECOSYSTEM ASSESSMENT, 2005

Global orchestration

A globally connected society focused

on global trade and economic

liberalization. Assumes a reactive

approach to ecosystem problems.

Takes strong steps to reduce poverty

and inequality and to invest in public

goods such as infrastructure and

education. Economic growth is the

highest of the four scenarios, while

population in 2050 is lowest (8.1 billion)

Order from strength

A regionalized and fragmented world,

concerned with security and protection,

emphasizing primarily regional markets,

paying little attention to public goods

and taking a reactive approach to

ecosystem problems. Economic

growth rate is the lowest (particularly in

developing countries) while population

growth is the highest of the scenarios

(9.6 billion in 2050)

Adapting mosaic

River catchment-scale ecosystems are

the focus of political and economic

activity. Local institutions are

strengthened and local ecosystem

management strategies are common,

with a strongly proactive (and learning)

approach. Economic growth is low

initially but increases with time.

Population in 2050 is high (9.5 billion)

Technogarden

A globally connected world relying on

environmentally sound technology,

using highly managed, often

engineered, ecosystems to deliver

ecosystem services, and taking a

proactive approach to ecosystem

management. Economic growth is

relatively high and accelerating, while

the 2050 population is midrange

(8.8 billion). This is the only scenario

to assume a climate policy (stabilizing

at 550 ppm)

GREENHOUSE

GAS

EMISSIONS

TO 2050

: 20.1 GtC-eq

: 3.7 GtC-eq

O: 1.1 GtC-eq

Other: 0.7 GtC-eq

: 15.4 GtC-eq

: 3.3 GtC-eq

O: 1.1 GtC-eq

Other: 0.5 GtC-eq

: 13.3 GtC-eq

: 3.2 GtC-eq

O: 0.9 GtC-eq

Other: 0.6 GtC-eq

: 4.7 GtC-eq

: 1.6 GtC-eq

O: 0.6 GtC-eq

Other: 0.2 GtC-eq

PREDICTED

TEMPERATURE

RISE TO 2050

AND 2100

2050: +2.0°C

2100: +3.5°C

2050: +1.7°C

2100: +3.3°C

2050: +1.9°C

2100: +2.8°C

2050: +1.5°C

2100: +1.9°C

LAND USE

CHANGES

TO 2050

Slow forest

decline to

2025, 10%

more arable

land

Rapid forest

decline to

2025, 20%

more arable

land

Slow forest

decline to

2025, 10%

more arable

land

Forest

increase to

2025, 9%

more arable

land

NITROGEN

TRANSPORT

IN RIVERS

TO 2025

Increased

nitrogen

in rivers

Increased

nitrogen

in rivers

Increased

nitrogen

in rivers

Decreased

nitrogen

in rivers

ECOSYSTEM

SERVICES

TO 2025

Provisioning

services

improved,

regulating and

cultural services

degraded

All ecosystem

services heavily

degraded

All ecosystem

services

improved

Provisioning and

regulating

services

improved,

cultural services

degraded

9781405156585_4_013.qxd 11/5/07 15:03 Page 452

Chapter 13 Habitat degradation

453

Physical and chemical impacts of human

activities

People physically degrade or chemically pollute

natural ecosystems when generating power or devel-

oping land for agricultural, urban and industrial

purposes. Humans are not unique among species in

degrading their environment, and when our popula-

tion density was low, and prior to our harnessing of

non-food energy, humans probably had no greater

impact than many other species. But now the scale of

human effects is proportional to our huge numbers

and advanced technologies.

Habitat degradation has costs in terms of human

health and lost ecosystem services, including pro-

visioning services (such as wild foods and drinking

water), cultural services (including educational and

recreational opportunities), regulating services (such

as the ecosystem’s ability to break down pollutants or

regulate climate) and supporting services (including

primary production and soil formation).

Degradation via cultivation

The intensive production of livestock in factory farming

is seriously polluting, and agricultural slurry may need

to be thinly dispersed over extensive farmland to dilute

it to a level that natural decomposers can deal with it.

Intensive agriculture is associated with an increase

in the nitrate and phosphate that runs into rivers, lakes

and oceans. The consequent eutrophication may be

counteracted by matching fertilizer supply to crop

demand, restoring natural wetlands (or constructing

artiﬁcial ones) to take up some of the excess nutrients

before they enter rivers and, in lakes, by biomanipulat-

ing the level of grazing on phytoplankton to increase

water clarity.

Many manufactured pesticides have become

important environmental pollutants. Problems arise

when pesticides are toxic to many more species than

just the target and particularly when they drift beyond

the target areas and persist in the environment.

The organochlorine insecticides have been particu-

larly problematic because they are progressively

biomagniﬁed in animals further up the food chain. Top

predators in aquatic and terrestrial food chains, which

were never intended as targets, can then accumulate

very high doses.

Cultivation can also physically degrade a landscape

through the loss of habitat diversity, while heavy irriga-

tion depletes water in rivers and changes their patterns

of ﬂow, with adverse consequences for river inhabitants.

Power generation and its diverse effects

Our use of fossil fuels has provided the power to

transform much of the face of the planet through

intensive agriculture, urbanization and industrial devel-

opment. The polluting effects of burning coal and oil

include acid rain, which can affect lakes and forests

in neighboring countries, and a dramatic increase in

atmospheric carbon dioxide, which is responsible for

climate change at the global level.

Recent emphasis has been placed on developing

alternative energy sources that do not release carbon

dioxide. The cleanest and safest technologies are

expected to derive from hydropower schemes (already

at a technologically advanced state in many parts of

the globe), together with wind farms (rapidly develop-

ing, but with potential adverse consequences for

migrating birds) and solar and wave power. Nuclear

power, whose popularity had declined because of

concerns over security and radioactive waste disposal,

is receiving renewed consideration because it does

not release greenhouse gases.

Degradation in urban and industrial landscapes

Our feces and urine create large disposal problems

in towns and cities because density is so high. At its

simplest, primary sewage treatment simply removes

most of the solid organic matter. Secondary treatment

mimics natural decomposition processes, eliminat-

ing organic matter but leaving high concentrations

of nitrate and phosphate in the waste water. Tertiary

treatment chemically removes these nutrients.

Exotic industrial chemicals also ﬁnd their way into

waterways and the atmosphere where they cause

diverse problems. For example, chloroﬂuorocarbon

compounds (CFCs), developed as aerosols and

SUMMARY

Summary

9781405156585_4_013.qxd 11/5/07 15:04 Page 453

Part IV Applied Issues in Ecology

454

refrigerants and used on a very large international

scale, were found to pose the threat that their chlorine

content could interact with and destroy atmospheric

ozone, which normally protects the worlds’ biota

from harmful UV radiation. International agreement

to phase out CFCs is expected to solve the problem

by 2050 (including recovery of the substantial ozone

hole that forms annually over Antarctica).

Mining activities, whether for fossil fuels or metals,

also cause physical and chemical degradation to

surrounding ecosystems. For example, more than

1 million tonnes of oil enters the world’s waterways

every year from wells drilled into the seabed or from oil

tankers, with adverse consequences for marine life.

Mining for metals such as copper may also pollute at

every stage of extraction, puriﬁcation and disposal.

Land that has been damaged by mining is usually

unstable, liable to erosion and devoid of vegetation.

The simplest solution to land reclamation is the re-

establishment of vegetation cover, because this will

stabilize the surface, be visually attractive and self-

sustaining. Candidate plants for reclamation are those

that are tolerant of the toxic heavy metals present.

Maintenance and restoration of ecosystem

services

The concept of ecosystem services brings into focus

three very different ways of looking at our effects on the

natural world – the triple bottom-line of environmental,

economic and sociopolitical perspectives. Planning

for sustainable use of natural resources usually needs

to be carried out at regional or global scales.

The impact of agriculture depends on the propor-

tion of the landscape that is used for production, and

planning needs to be done at the regional scale and

involve the knowledge of experts in environmental,

economic and sociological disciplines. Dealing with

the diversity of views among neighbors is difﬁcult

enough, but our biggest environmental problem –

climate change due in large measure to the burning

of fossil fuels – requires a multinational, global level

of planning.

REVIEW QUESTIONS

Review questions

Asterisks indicate challenge questions

1 What are the features that distinguish human

pollution of the environment from that by other

social organisms?

2 Explain why it may be impossible to achieve

increasing agricultural production without

creating unacceptable levels of nitrate in

drinking water.

3* Consider the toilet that you most frequently use.

Find out where your sewage goes and how it is

treated. What pollution problems are you

contributing to as a result of your sewage

disposal?

4 Describe the causes of acid rain and the way

in which it damages terrestrial and aquatic

communities.

5* Hydroelectric schemes provide one of the least

polluting ways of generating power.

Nevertheless, they have a number of negative

effects on natural systems. What are they?

6 Deﬁne the characteristics that make some

pesticides particularly dangerous pollutants.

7 Describe the ways in which the use of metals by

humans has created problems of environmental

pollution.

8 Deﬁne the greenhouse effect and list the

pollutants that contribute to it.

9* Review the case of the Asian vultures heading

to extinction (see Section 1.3.4) and describe

the ecosystem services that would be lost with

the vultures. In outline, describe how economic

value could be estimated for these services.

10* It is often argued that environmental pollution

can be prevented only by ‘making the polluter

pay’. Discuss the ways in which this is, or might

be, done.

9781405156585_4_013.qxd 11/5/07 15:04 Page 454

455

Chapter 14

Conservation

CHAPTER CONTENTS

14.1 Introduction

14.2 Threats to biodiversity

14.3 Conservation in practice

14.4 Conservation in a changing world

14.5 Finale

Chapter contents

KEY CONCEPTS

In this chapter you will:

recognize that in seeking to conserve the Earth’s species and

communities, we are often woefully ignorant of what there is to

conserve

appreciate that endangered species are usually rare, but not all rare

species are endangered

understand that some species are at risk for a single reason, such as

overexploitation, habitat disruption or introduced species, but often

a combination of factors is at work

recognize that populations that become very small may experience

genetic problems

understand that conservation involves the development of species

management plans but also often requires a broader, community

perspective

appreciate that global climate change further complicates conservation

planning

Key concepts

9781405156585_4_014.qxd 11/5/07 15:05 Page 455

14.1 Introduction

The term biodiversity makes frequent appearances in both the popular media and

the scientiﬁc literature – but it often does so without an unambiguous deﬁnition.

At its simplest, it is species richness, the number of species present in a deﬁned

geographic unit (see Chapter 10). Biodiversity, though, can also be viewed at scales

smaller and larger than the species. For example, we may include genetic diversity

within species, perhaps seeking to conserve genetically distinct subpopulations and

subspecies (see Chapter 8). Above the species level, we may wish to ensure that

species without close relatives are afforded special protection, so that the overall

evolutionary variety of the world’s biota is maintained as large as possible. At a larger

scale still, we may include in biodiversity the variety of community types present

in a region – swamps, deserts, early and late stages in a woodland succession and so

on. Thus, ‘biodiversity’ may itself, quite reasonably, have a diversity of meanings.

Yet it is necessary to be speciﬁc if the term is to be of any practical use. Ecologists

must deﬁne precisely what it is they mean to conserve in their particular circum-

stances, and how to measure whether this has been achieved.

Most often the focus of concern of conservation biologists is the rate of extinc-

tion of species in the face of human inﬂuence. To judge the scale of this problem,

we need to know the total number of species that occur in the world, the rate at

which these are going extinct and how this rate compares with that of pre-human

times. Unfortunately, there are considerable uncertainties in our estimates of all

these things. About 1.8 million species have so far been named (Figure 14.1), but

the real number must be much larger. Estimates have been derived in a variety

of ways. One approach, for example, uses information on the rate of discovery of

new species to project forward, group by taxonomic group, to a total estimate of

up to 6–7 million species in the world. However, the uncertainties in estimating

global species richness are profound and our best guesses range from 3 to 30 million

or more (Gaston, 1998).

An important lesson from the fossil record is that the vast majority of (probably

all) species eventually become extinct – more than 99% of species that ever

existed are now extinct. However, given that individual species are believed, on

average, to have lasted about 1–10 million years, and if we estimate conservatively

that the total number of species on Earth is 10 million, we would predict that only

an average of between 100 and 1000 species (0.001–0.01%) would go extinct each

Part IV Applied Issues in Ecology

456

what is biodiversity?

Natural ecosystems have been placed at threat by a plethora of human inﬂuences,

particularly in the face of a burgeoning human population. Conservation is the

science concerned with increasing the probability that the Earth’s species and

communities (or, more generally, its biodiversity) will persist into the future.

We need to appreciate the scale of the problem, understand the threats posed

by human activities and consider how our knowledge of ecology can be

brought to bear to provide remedies.

estimates of the number of

species on Earth range from 3

to 30 million or more

modern extinction rates

compared to historical

extinction rates

9781405156585_4_014.qxd 11/5/07 15:05 Page 456

Chapter 14 Conservation

457

Algae, amoebae, etc.

012345678

Number of species (in millions)

Insects, centipedes and millipedes

Spiders, mites, etc.

Fungi

Nematodes, worms

Plants

Mollusks

Crustaceans

Vertebrates

Named species

Unnamed species (estimate)

Figure 14.1

Numbers of species identiﬁed and

named (maroon histograms) and

estimates of unnamed species that

exist (green histograms).

MODIFIED FROM MILLENNIUM ECOSYSTEM ASSESSMENT, 2005

14.1 TOPICAL ECONCERNS

14.1 Topical ECOncerns

To most people, biological diversity is undeniably of

value but standard economics has generally failed

to assign value to ecological resources. Thus, the

costs of environmental damage or depletion of living

resources have frequently been disregarded. A major

challenge is the development of a new ecological

economics (Costanza et al., 1997) in which the worth

of species, communities and ecosystems can be

assigned ﬁnancial value to be set against the gains

to be made in industrial and other human projects

that may damage them. As we saw in Section 13.1.2,

the value of biodiversity can be measured in terms

of the ‘free’ ecosystem services it provides.

Many species have direct value and many more

are likely to have a potential value that as yet remains

untapped. For example, wild meat, ﬁsh and plants

remain vital resources in many parts of the world,

while most of the world’s food is derived from plants

that were originally domesticated from wild plants in

tropical and semiarid regions. In future, wild strains of

these species may be exploited for their genetic diver-

sity, and quite different species of plants and animals

may be found that are appropriate for domestication.

Secondly, as we saw in Chapter 12, the potential

beneﬁts that might come from natural enemies if they

could be used as biological control agents for pest

What is the value of biodiversity?

century. The current observed rate of extinction of birds and mammals of about

1% per century is 100–1000 times this ‘natural’ background rate. Furthermore,

the scale of the most powerful human inﬂuence, habitat destruction, continues

to increase.

The evidence, then, while inconclusive to a degree because of the unavoidable

difﬁculty of making accurate estimates, suggests that our children and grand-

children may live through a period of species extinction comparable to the

‘natural’ mass extinctions evident in the geological record (see Section 10.6).

But should we care? To most, the answer is a resounding and unhesitating ‘Yes’.

Whether the answer seems obvious or debatable, however, it is important to

consider why we should care – why biodiversity is valuable (Box 14.1).

9781405156585_4_014.qxd 11/5/07 15:05 Page 457

Part IV Applied Issues in Ecology

458

species are enormous; most natural enemies of

most pests remain unstudied and often unrecognized.

Finally, about 40% of the prescription and non-

prescription drugs used throughout the world have

active ingredients extracted from plants and animals.

Aspirin, probably the world’s most widely used drug,

was derived originally from the leaves of the tropical

willow, Salix alba. The nine-banded armadillo (Dasypus

novemcinctus) has been used to study leprosy and pre-

pare a vaccine for the disease; the Florida manatee

(Trichechus manatus), an endangered mammal, is

being used to help understand hemophilia; while the

rose periwinkle (Catharanthus roseus), a plant from

Madagascar, has yielded two potent drugs effective in

treating blood cancer. In all these cases, the species can

be thought of as representing provisioning ecosystem

services (see Section 13.1.2).

Other species have indirect economic value.

For example, many wild insects are responsible for

pollinating crop plants. This is another provisioning

service. In a different context, the monetary value

of ecotourism, which depends on biodiversity, is

becoming ever more considerable. Each year, nearly

200 million adults and children in the USA take part

in nature recreation and spend about $4 billion on

fees, travel, lodging, food and equipment. Moreover,

ecotourists, who visit a country wholly or partly to experi-

ence its biological diversity, spend approximately

$12 billion a year worldwide on their enjoyment of

the natural world (Primack, 1993). On a smaller scale,

a multitude of natural history ﬁlms, books and edu-

cational programs are ‘consumed’ annually without

harming the wildlife upon which they are based. In these

contexts, biodiversity provides cultural ecosystem

services. More ingenuity is required to ﬁnd ways to

measure the indirect economic beneﬁts that accrue

as a result of natural biodiversity; for example, bio-

logical communities can be of vital importance by

maintaining the chemical quality of natural waters, in

buffering ecosystems against ﬂoods and droughts,

in protecting and maintaining soils, in regulating local

and even global climate, and in breaking down or

immobilizing organic and inorganic wastes. All of these

are regulating ecosystem services.

It should be noted that many people point to

ethical grounds for conservation, with every species

being of value in its own right – a value that would still

exist even if people were not here to appreciate or

exploit them. From this perspective even species with

no conceivable economic value require protection.

It would be wrong, though, to see things only from

the point of view of conservation – not that there are

really arguments against conservation as such, but

there are arguments in favor of the human activities

that make conservation a necessity: agriculture, the

felling of trees, the harvesting of wild animal popula-

tions, the exploitation of minerals, the burning of

fossil fuels, irrigation, the discharge of wastes and

so on. To be effective, it is likely that the arguments

of conservationists must ultimately be framed in

cost–beneﬁt terms because governments will always

determine their policies against a background of the

money they have to spend and the priorities accepted

by their electorates.

A government conservation authority is considering

a proposal to designate a marine reserve at a rocky

promontory of great scenic beauty. The site is very

diverse in species, including a few that are rare. Com-

mercial and recreational ﬁshers wish to continue

ﬁshing at this unusually productive site, local people

have mixed feelings about an expected inﬂux of

tourists, while conservationists (who mostly live a long

way from the site) believe that the conservation value

is such that no ﬁshing should be permitted and visitor

numbers should be strictly controlled. Imagine that you

are an arbitrator chairing a meeting of all interested

parties. What arguments do you think they will put

forward? What decision would you reach and why?

9781405156585_4_014.qxd 11/5/07 15:05 Page 458