12.5 Conservation of Biological Diversity and the Global Environment | Introduction to Life Science | University of Tokyo


12.5Conservation of Biological Diversity and the Global Environment


Ecological Balance and Environmental Conservation

Generally, although the composition of trophic levels and the number of individuals of each species in natural ecosystems or biocenoses vary to a certain degree, these are often maintained within a certain scope. This is called the balance of ecosystems (continuance, persistence). This balance is maintained through the restoring force (resilience) of ecosystems to return to their original state even if they are disrupted slightly because of the activities that maintain the continuance of this system as a whole.
With a wide species composition of animals and plants in them, climax forests are an ecosystem that maintains its balance in material cycling and energy transfer, etc. However, excessive human activities such as logging of forests, grazing of hilly areas, and development of building land and golf courses often simplify biocoenoses that consist of many species, and weaken various regulatory functions that occur in natural ecosystems, thereby changing ecosystems.
Furthermore, forests in original natural ecosystems where there is no human intervention are in part designated as natural parks such as national parks and world heritage, etc., and conservation measures are being established to ensure that no land development without permission takes place.

■Conservation of Forest Ecosystems
Since ancient times, the Japanese have considered forests as immediate access to nature and an important resource. Forests were preserved by not logging timber unilaterally, afforestation of logged vacant lots, use of firewood and charcoal as fuels, and trimming of bottom weeds. This is the manner in which the so-called Satoyama is used. Satoyama is a secondary ecosystem (a natural ecosystem with human intervention involved), and even in this, peculiar animals and plants exist. Examples are the seven autumn herbs (Eupatorium japonicum etc.). At the degree of slight disruption through human intervention between whiles, the forest does not become a climax forest, and many species make bright forests in a secondary transient state their habitat. However, in recent years, such Satoyama have been vanishing rapidly as they have been left unattended or replaced by land developments. There is therefore an urgent need for conservation methods.

■Conservation of Aquatic Ecosystems

Fig. 12-13. Plankton Constituting Red Tides

Tidal wetlands are rich in microbial activity, and constitute an ecosystem in which a variety of animals, such as sandworms, clams, and crabs reside. These animals act as decomposers by eating detritus and microbes contained in the seawater and mud, thus helping purify the seawater. Therefore, the tidal wetlands of inner bays are indispensable for the activity of fishing villages. However, the flow of domestic as well as industrial and agricultural wastewater in large quantities into the sea exceeds the natural purification effect of tidal wetlands. Furthermore, recent bank protection works are rapidly demolishing tidal wetlands. As a result, the concentration of organic material and nitrogen as well as phosphorus rapidly increases and causes eutrophication in inner bays, in which case high densities of particular plankton can generate red tides (Fig. 12-13). During a red tide, when these plankton die, they consume a large amount of oxygen, causing hypoxic conditions. In some cases, and certain types of plankton secrete a material harmful to fish, which in the end, have some impact on the aquatic ecosystems.
Blue-green algae in lakes and marshes are caused by the same phenomena through explosive increase of cyanobacteria. As a result, the water of the lakes becomes hypoxic, and toxins (cyanotoxins) secreted by the cyanobacteria, which cause foul smell, severely affect the aquatic ecosystem.


Global Warming—An Inconvenient Truth, and Reception of the Nobel Peace Prize by the IPCC

In 2007, the Nobel Peace Prize was awarded to Al Gore, the former vice-president of the United States of America, and to the Intergovernmental Panel on Climate Change (IPCC). The prize recognized their joint efforts regarding global warming. Gore was defeated in the tight race of the American presidential election by a very slight margin, following which he intensified his efforts to tackle the problem of global warming as a politician. He appeared in An Inconvenient Truth, which was awarded with the full-length documentary film prize of the Academy Awards, and expanded enlightenment activities to speed up the ringing of the alarm bells of global warming on a global scale through TV programs and book publications.
On the other hand, the IPCC—an international organization with about 2,500 researchers working—established the UN Environment Program (UNEP) and the World Meteorological Organization (WMO) in 1988 with the purpose of forecasting climate changes related to global warming resulting from the greenhouse effect and evaluating the effects on nature and the social economy as well as measures. The IPCC consists of three working groups (WG). WG 1 evaluates the scientific grounds of climate systems and climate change. WG 2 evaluates social-economic systems against climate change, the vulnerability of ecosystems, the effects of climate change, and coping measures. And WG 3 evaluates measures for controlling the emission of greenhouse gases, and measures for alleviating climate change. The fourth assessment report, November 2007, was published in series with more than 450 representative writers from 130 countries and territories, more than 800 collaborative authors and 2500 experts as referee readers. Also in Japan, a large number of researchers from institutions such as the National Institute for Environmental Studies, Tokyo University, the Japan Agency for Marine-Earth Science and Technology, and the National Institute of Polar Research contributed to this report.


Introduced Species

Column Fig. 12-2. Various Introduced Species

Species that are brought intentionally by humans or carried by chance from their country of origin, and that have become established in a new area are referred to as introduced or naturalized species. Typical examples are dandelion (Taraxacum officinale), Canada goldenrod (Solidago altissima), American bullfrog (Rana catesbeiana), crayfish (Proambarus clarkii), green tree cricket (Calyptotrypus hibinonis), and recently, black bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) (Column Fig. 12-2). In particular, cities comprises artificial environments and lakes in their vicinity, usually have open niches and no natural enemies that exist across the land. As these introduced species penetrate open niches, they gradually reach a high density and eventually spread. The fact that domestic species such as weatherfish (Misgurnus anguillicaudatus), crucian (Fagus crenata), carp (Cyprinus carpio), black-spotted pond frog (Rana nigromaculata), and dandelion (Taraxacum platycarpum Dahlst), which are all familiar through Japanese nursery rhymes and songs, have been outnumbered by introduced species, in a way, pose a risk to Japanese culture.
The fall webspinner (Hyphantria cunea) was brought by chance around 1945 from North America to Tokyo. Thereafter, it spread all over Japan and became a domesticated harmful insect. Its larvae increase explosively in metropolitan environments and damage the leaves of roadside trees by eating them. However, they have not spread to the natural countryside. This is because if there is a huge variety of species that menace ecosystems, natural enemies of its predators make a variety of habitats. The mechanism that suppresses the number of fall webspinners works. Furthermore, because the ecosystems of cities are rather simple and there are only few predators and competitors, fall webspinners can sufficiently exploit the resources of the leaves of roadside trees.
In Japan, the Invasive Alien Species Act was put into effect in June 2005. Since then, specified introduced species, which largely affect domestic species, have been regulated with regard to feeding, cultivation, storage, transport, and import, etc. The number of specified animal species such as Taiwan macaque (Macaca cyclopis), common raccoon (Procyon loton), largemouth bass (Micropterus salmoides), American bullfrog (Rana catesbeiana), Java mangoose (Herpestes javanicus), and bumble bee (Bombus terrestris), as well as plants such as Hydrocotyle ranunculoides and Sicyos angulatus are steadily increasing.

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Habitat Fragmentation and the Risk of Extinction of Populations

When roads are constructed as a part of environmental development in natural ecosystems such as continuous forests, a large area of the forest, which until then was an uninterrupted habitat of certain populations, is divided into various parts and gradually changes into detached small clutches of groves. The emergence of several wide streets considerably disturbs the coming and going of small wild animals along trails. Such a state is called fragmentation, and the segregated state of these various local populations is called isolation.
Since fragmented local habitats become small in size, local individual populations that remain in those habitats reduce in size as well. A small group that is becoming increasingly isolated is likely to become extinct soon. This is because as local populations shrink in size, the following factors set out to affect one another.

■Demographic Probability
One factor that makes local populations extinct is demographic probability (temporary pause of the number of live births and sex ratio bias) within the population. Generally, populations with sufficient numbers of individuals see the temporary pause in the number of live births of one female close to the expected value of the animals per se and also see the sex ratio between males and females close to 1:1. In contrast, small local populations stochastically see no offspring born or the disproportionate birth of only one sex occur even though the parents are healthy. As a result, in small populations, the reproductive power often drops, causing an increased risk of extinction of local populations.

■Inbreeding Depression
Inbreeding depression as a result of relative mating is also related to this problem. In large populations, even if mutations cause recessive alleles to appear with deleterious traits, it will not appear as a phenotypic character as long as this allele becomes heterozygous with a dominant gene. In local populations, however, it is seldom that the mating partner comes from another population. Thus, cases of inbreeding among relatives born from a small number of parents become frequent, and as the percentage of adverse alleles to becoming homozygous increases in the group newer offspring, inbreeding depression appears.

■The Interlocking Effects of Extinction Promoting Factors
There are also some other factors that are known to bring local populations to extinction (the fixation of weakly harmful genes as a result of genetic drift, etc.). Also these various factors do not act independently, but are accompanied by interlocking effects. If by chance a certain percentage of the natural ecosystems in one area is harmed through artificial environmental development, this may trigger other extinction promoting factors to start to act. Furthermore, if the number of individuals decreases, this will gradually result in an extinction vortex due to other factors acting together (Fig. 12-14).

Fig. 12-14. Schematic Diagram of an "Extinction Vortex" Caused by the Interlocking Effects of Extinction Promoting Factors

When a population has shrunk by chance as a result of environmental development, etc., it can trigger the onset of interlocking of various extinction promoting effects. The direction of arrows shows that this cycle produces an interlocked enhancement effect.


Endocrine Disrupters

Endocrine disrupters are exogenous materials found in the environment that disturb the synthesis and secretion of hormones in organisms, e.g., their transport in blood, binding to receptor and breakdown, etc. From the end of the 1960s, it was already pointed out that DDT and other such chemicals may exert hormone-like effects. However, Our Stolen Future, which was published in 1997 by the author Theo Colborn, attracted attention because it rang an alarm. In Japan, in May 1998 at one burst, the media were flooded by the word "environmental hormones" (the word "hormone" was obviously misemployed) after the environment Agency at that time (now Environment Ministry) had listed 67 harmful substances in Strategic Plan for Environmental Endocrine Disrupters (SPEED 1998).
Candidate materials included agricultural chemicals (DDT, BHC, etc.), dioxins, and chlorinated organic compounds such as polychlorinated biphenyl (PCB), organotin compounds such as tributyltine (TBT) and triphenyltin (TPT), as well as alkyl phenols (bisphenol A, nonyl phenol), which were added by the Environment Ministry in 2001. Initially, examples included the observation of the feminization of more than 140 kinds of male shellfish (TBT and TPT), intersexuality of marine mollusk resulting from organotin compounds which are used as ship bottom paint (TBT), the feminization of cyprinid fresh water fish roach etc. (nonylphenol). However, recent research on killifish confirmed the endocrine disrupting effects of bisphenol A and nonylphenol, while experiments using mice did not confirm the endocrine disrupting effects of DDT and bisphenol A when given at low doses. The effects of DDT on the reproduction and breeding of birds, as well as causative agents in nature regarding reproductive abnormalities of wild animals have not been specified yet. Also, the relationship between the decrease in sperm numbers and the decline in the function of the testis in humans and endocrine disrupters remains uncertain. As research advances, we'll just have to wait and see with those examples available.

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Conservation of Biodiversity

For the conservation of biodiversity, it is desirable that an ecosystem in which protected species live is left in a protected habitat that is as wide as possible. Regarding the argumentation of the planning of protected habitats, there is the SLOSS problem. This is an important issue regarding whether from the aspect of the estimated costs for the set up of a protected habitat, the area should be used as a single large protected habitat or partitioned into several small protected habitats when it is not possible to reserve an area of sufficient size as a protected habitat. Since in the case of larger carnivorous mammals, a large limited territory is required, even if various small protected habitats are set up, there is a possibility that they all will become too narrow. On the other hand, if in the case of small animals (birds and insects) which can fly, several small protected habitats are set up this is largely unproblematic even if they are small, since it is possible for the animals to migrate and disperse between them, and since even if a bush fire would break out at one protected habitat, spreading of the fire to the other protected habitats would be avoided. Thus, it is necessary to design protected habitats which are best suited with regard to the migration and dispersion ability of the organism which is to be protected.
Depending on the migration force and flying power of animals, and in the case of plants, depending on the dispersing ability of pollen and seeds, it is determined to which extent their isolation can be proceeded. For this purpose, attempts are being made to prevent the isolation of local populations by making migration between local populations possible by constructing small tunnels under roads so that wild animals can move around, and laying out shrub hedges, etc. at the roadside of developed residential areas. Furthermore, regarding wild animals with a high risk of extinction, together with the establishment of protected habitats, experiments with respect to feeding and artificial breeding, reproduction and child-care are being conducted, to increase their number when they are returned to nature.

Fig. 12-15. Three Factors that Define Biodiversity

The 3 factors of biodiversity are species diversity, genetic diversity, and diversity of ecosystems (Fig. 12-15). One can say that the field of ecological science plays a very important role for the conservation of biodiversity. In recent years, a large international project (DIVERESTAS) for the advancement of research on the conservation of biodiversity is being designed, and for the people who live in the 21st century, further development of ecological science is being anticipated.


Red Data

For conserving biodiversity, species with a high risk of extinction are designated or indigenous ecosystems or biocenoses found in certain areas are designated and conserved. The degree of risk of extinction is classified into various categories, and a tabulated record of the species, subspecies, and populations of wild animals, which inhabit a certain area and corresponds to this classification is called a red list, and the book in which these are listed is called the red data book. The International Union for Conservation of Nature and Natural Resources (IUCN) publishes a red data book every few years, which includes information regarding worldwide endangered species. Depending on a number of criteria such as the rate of decrease of the number of individuals, the size of the area of the habitat, the total number of individuals, the distribution of reproductive populations, the number of mature individuals, and the probability of extinction, the degree of risk of extinction is classified into three categories: critically endangered (CR), endangered (EN) and vulnerable (VU). In the red list presented by the IUCN in 2003, 12,357 animal and plant species were classified as endangered species. In a recent report by the IUCN, it is mentioned that about 30 percent of the world's primates such as gorilla and orangutan are at the risk of extinction. It has been pointed out that currently 114 of 394 primate species that have been identified are feared to become extinct due to severe deforestation, illegal hunting, capture for use as a pet, and global warming, etc.


The National Biodiversity Strategy of Japan

For conservation of biodiversity, a national biodiversity strategy has been approved in a Cabinet meeting in Japan in March 2002, and as a result, a new grand design of the national program for land development has been unveiled. Currently, the content is being revised with regard to the third national biodiversity strategy of Japan. By this national biodiversity strategy, public policies are being conducted with the aspiration to conserve biodiversity, based on the following "three dangers."

1) The danger that as a result of human activity and development, species diminish or become extinct, and ecosystems become destroyed or fragmented due to development of forests, and landfilling destroying littoral ecosystems.
2) The dangers resulting from reduced intervention of humans in nature, more specifically the danger of deterioration of secondary ecosystems, which have been used for a long period of time as village-vicinity mountains and coastlines, due to abandonment as a result of a changed social situation.
3) The dangers resulting from introduced species and chemical agents, more specifically, the danger that Japan's biodiversity is harmed by foreign species, or the dangers of the environmental burden caused by chemicals such as PCB, DDT, and dioxin.

As described above, from the viewpoint of the conservation of biodiversity, it is important that in the 21st century, with regard to the current situation of the continuing destruction of ecosystems, concrete guidelines for national land development and public projects be released.

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