Part IV Applied Issues in EcologyPart IV Applied Issues in Ecology

鄭先祐 (Ayo)國立臺南大學 環境與生態學院生物科技學系 生態學 (2008)

Essentials of Ecology 3rd. Ed.

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ContentsContents• Preface• Acknowledgments• Part I: Introduction:• Part II: Conditions and Resources:• Part III: Individuals, Populations, Communities

and Ecosystems: • Part IV: Applied Issues in Ecology:

– 12. Sustainability ( 可持續力 )– 13. Habitat degradation ( 棲地衰退 )– 14. Conservation ( 保育 )

• References• Index

Chap.12 SustainabilityChap.12 Sustainability鄭先祐 (Ayo)

國立臺南大學 環境與生態學院生物科技學系 生態學 (2008)

Essentials of Ecology 3rd. Ed.

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SustainabilitySustainability

• 12.1 introduction• 12.2 the human population problem• 12.3 harvesting living resources from the

wild• 12.4 the farming of monocultures• 12.5 pest control• 12.6 integrated farming systems• 12.7 forecasting agriculturally driven global

environmental change

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12.1 introduction12.1 introduction

• What is sustainability?– To call an activity ‘sustainable’ means that it can be

continued or repeated for the foreseeable future.

• Ecological Society of America published (1991) the sustainable biosphere initiative: an ecological research agenda.

• And in the same year, the World Conservation Union, the United Nations Environment Program and the World Wildlife Fund for Nature jointly published Caring for the Earth, A Strategy for Sustainable Living (IUCN/UNEP/WWF)

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• The emphasis shifted more recently from a purely ecological perspective to one that incorporates economic and social conditions that influence sustainability.

• The Millennium Ecosystem Assessment, based on contributions from a large number of natural and social scientists, has as its aim providing both the general public and decision-makers with ‘a scientific evaluation of the consequences of current and projected changes in ecosystems for human well-being.

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12.2 the human population problem12.2 the human population problem

• The present size of the global human population is unsustainably high. 

• Around AD200, when there were about a quarter of a billion people on Earth. 

• By 2005 the total had risen to an estimated 6.5 billion (United Nations, 2005).

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• It is not the size but the distribution over the Earth of the human population that is unsustainable. 

• The fraction of the population living, highly concentrated, in an urban environment has risen from around 3% in 1800 to 29% in 1950 and 47% in 2000. 

• Each agricultural worker today has to feed her-or himself plus one city dweller, by 2050 that will have risen to two urbanites (Cohen, 2005).

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• The present rate of growth in size of the global human population is unsustainably high. 

• Prior to the widespread agricultural revolution of the 18th century, the human population , very roughly, had taken 1000 years to double in size. 

• The most recent doubling took just 39 years (Cohen, 2001)

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• It is not the size but the age distribution of the global human population that is unsustainable. 

• In the ‘developed’ regions of the world, the percentage of the population that was elderly (over 65) rose from 7.6% in 1950 to 12.1% in 1990. 

• This proportion will jump dramatically after 2010 when the large cohorts born after World War II pass 65.

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• It is not the size but the uneven distribution of resources within the global population that is unsustainable. 

• In 1992, the 830 million people of the world’s richest countries enjoyed an average income equivalent to US$22,000 per annum.   The 2.6 billion people in the middle income countries received $1,600.  But the 2 billion in the poorest countries got just $400.  These averages themselves hide enormous inequalities.

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Discuss Questions:Discuss Questions:

1. What role or responsibility does the individual, as opposed to government, have in responding to the human population problem?

2. Which of the variants of the problem, above, pose particular questions of the relationship between the developed and the developing parts of the world or between the ‘haves’ and the ‘have nots’?

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• Fig.12.1 the growth of human populations

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• Fig. 12.2 the decline in the annual rate of population growth in Europe since 1850 has been associated with a decline in the death rate, followed by a decline in the birth rate, and an overall narrowing of the gap between the two.

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• Fig. 12.3 population growth rate averaged for the world as a whole from 1950 to 2050

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Three unique transitions:Three unique transitions:1. Until now, young people (e.g. the 0-4 years

class) have always outnumbered old people (e.g. the 60+ years class), but from 2000 the old will outnumber the young.

2. Until now, rural people have always outnumbered urban people, but from approximately 2007 urban people will predominate.

3. From 2003 onward, women, on average, worldwide have had, and will continue to have, too few or just enough children during their lifetime to replace themselves and the children’s father in the next generation.

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• Fig. 12.4 predicted population size and age structure in 2050 for the less developed and more developed countries of the world.

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A global carrying capacity?A global carrying capacity?• In 1679, van Leeuwenhoek estimated that the

inhabitated area of the Earth was 13,385 times larger than his home nation of Holland, whose population then was about 1 million people. Roughly about 13.4 billion.

• In 1967, De Wit asked the question ‘ How many people can live on Earth if photosynthesis is the limiting process?’ The answer he arrived at was roughly 1,000 billion.

• In 1970, Hulett estimated the figure was no more than 1 billion.

• Kates and others, in a series of reports from 1988, 5.9 billion ( 素食 ) ， 3.9billion(15% 肉 ) ， 2.9billion (25%肉 ) 。

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A global carrying capacity?A global carrying capacity?

• Wackernagel and his colleagues in 2002 sought to quantify the amount of land humans use to supply resources and to absorb wastes (footprint concept). Their preliminary assessment was that people were using 70% of the biosphere’s capacity in 1961 and 120% by 1999.

• They reasoned, in other words, that global carrying capacity was exceeded before the turn of the millennium – when our population was about 6 billion.

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12.3 harvesting living resources from the wild12.3 harvesting living resources from the wild

– Primitive human societies obtained all their resources by hunting and gathering from nature, and humans continue to garner some resources in this way.

• 12.3.1 Fisheries: maximum sustainable yields• 12.3.2 obtaining MSYs through fixed quotas• 12.3.3 obtaining MSYs through effort• 12.3.4 Beyond MSYs

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• Fig. 12.5 Changes in the contribution to global marine fish production made by fisheries in different phases of their exploitation.

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• Fig. 12.6 The humped relationship between the net recruitment into a population (birth minus deaths) and the size of that population, resulting from the effects of intraspecific competition.

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Maximum sustainable yieldMaximum sustainable yield

• Populations in the absence of exploitation can be expected to settle around their carrying capacity, but exploitation will reduce numbers to less than this

• Exploitation, by reducing the intensity of competition, moves the population ‘leftwards’ along the humped net recruitment curve, increasing the net number of recruits to the population per unit time (Fig. 12.6)

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• Fig. 12.7 fixed quota harvesting.• The figure shows a single recruitment curve (solid line)

and two fixed quota harvesting curves (dashed lines).

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• Fig. 12.8 Landings of the Peruvian anchovy( 鯷魚 ) since 1950. Note the dramatic crash that resulted mainly as a result of overfishing. The stock has taken 20 years to rebuild.

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12.3 obtaining MSYs through fixed effort12.3 obtaining MSYs through fixed effort

• An alternative to trying to maintain a constant harvest is to maintain a constant ‘harvesting effort’.

Fig. 12.9 Fixed effort harvesting.

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Beyond MSYsBeyond MSYs

• Environmental fluctuations, such as El Nino events

• A strategy of taking only intermediate-sized fishes

• Precautionary management

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• Fig. 12.10 predictions for the stock of Arctic cod under three intensities of fishing and three different sizes of mesh in the nets.

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• Fig. 12.11 The black rockfish off the coast of Oregon, USA, is a long-live fish that produces live young.

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12.4 the farming of monocultures12.4 the farming of monocultures

• Between 1961 and 1994 the per capita food supply in developing countries increased by 32% and the proportion of the world’s population that was undernourished fell from 35% to 21%, though this is very unevenly distributed.

• Yet 800 million people remain hungry worldwide, and the rate of increase in per capita food production is falling.

• Only monoculture can maximize the rate of food production.

• But disease spreads in monocultures.

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Fig. 12.12 Agricultural monoculture: wheat as far as the eye can see.

Fig. 12.12 Agricultural monoculture: wheat as far as the eye can see.

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• Dust bowl field and abandoned farm

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The sustainability of water as a resourceThe sustainability of water as a resource

• In the 1960s and 1970s, the main worry about the sustainability of global resources concerned energy supplies that were recognized to be finite and exhaustible.

• Water has now come into sharper focus.• Fresh water, which is used in crop irrigation and

for domestic consumption, is of crucial importance.

• On a global scale, agriculture is the largest consumer of fresh water, taking more than 70% of available supplies and more than 90% in parts of South America, central Asia and Africa.

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• Fig. 12.14 water availability per person from region to region of the globe in 2000. The units are in cubic meters per capita per year.

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圖 1.地下水層污染的熱點 (Hotspots)。這是根據在學術文獻的資料。因為全球大部分地區仍然沒有完全的監測，目前這個圖表現的只是真實現況的部分情形。

圖 1.地下水層污染的熱點 (Hotspots)。這是根據在學術文獻的資料。因為全球大部分地區仍然沒有完全的監測，目前這個圖表現的只是真實現況的部分情形。

砷

農藥 溶劑

石油化學

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12.5 Pest control12.5 Pest control

• What is a pest?– A pest species is simply one that humans

consider undesirable.– Estimates suggest that there are around

67,000 species of pests that attack agricultural crops worldwide: 8,000 weeds that compete with crops, and 9,000 insects and mites and 50,000 plant pathogens that attack them.

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12.5.1 economic injury levels and action thresholds

12.5.1 economic injury levels and action thresholds

• Economics and sustainability are intimately tied together.– Market forces ensure that uneconomic

practices are not sustainable.

• One might imagine that the aim of pest control is total eradication of the pest, but this is not the general rule.– The economic injury level (EIL)

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• Fig. 12.15 (a) The population fluctuations of hypothetical pest.

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• Fig. 12.16 Global increases in the number of arthropod pest species reported to have evolved pesticide resistance and in the number of pesticide compounds against which resistance has developed.

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12.5.3 biological control12.5.3 biological control

• Three types of biological control1. The importation of a natural enemy

– 引入外來的天敵2. Conservation biological control

– Native predators

3. Inoculation ( 預防接種 ) biological control– 通常使用於封閉空間 ( 溫室 )– 清空後，引入昆蟲的掠食者，清除害蟲。

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Table 12.1Table 12.1

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12.6 integrated farming systems12.6 integrated farming systems

• Integrated pest management (IPM)– IPM combines physical control, cultural

control, biological and chemical control and the use of resistant crop varieties.

– It has come of age as part of the reaction against the unthinking use of chemical pesticides in the 1940s and 1950s.

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• Fig. 12.18 Decision flow chart for the integrated pest management of potato tuber moths in New Zealand.

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• Fig. 12.19 Fruit yields of three apple production systems.

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12.7 Forecasting agriculturally driven global environmental change

12.7 Forecasting agriculturally driven global environmental change

• Fig. 12.20 Projected increases in nitrogen (N) and phosphorus (P) fertilizers, irrigated land, pesticide use and total areas under crops and pasture by the years 2020(maroon bars) and 2050 (green bars).

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Review questions IReview questions I

1. What is sustainability? Is it possible to have sustainable population growth? Sustainable use of fossil fuels? Sustainable use of forest trees? Justify your answers.

2. The number of people that the Earth can support depends on their standard of living. Argue the case either for or against developing nations having the right to expect standards of living those in the developed world take for granted.

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Review questions IIReview questions II3. Hilborn and Walters (1992) have suggested that there

are three attitudes that ecologists can take when they enter the public arena. The first is to claim that ecological interactions are too complex, and our understanding and our data too poor, for definite pronouncements to be make (for fear of being wrong). The second possibility is for ecologists to concentrate exclusively on ecology and arrive at a recommendation designed to satisfy purely ecological criteria. The third recommendation that are as accurate and realistic as possible but to accept that these will be incorporated with a broader range of factors when management decisions are made– and may be rejected. Which of these do you favor, and why?

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