Introduction to Ecology

This and the following pages conform the content included in :
Science Education Key Learning Area, Biology Curriculum and Assessment Guide (Advaned Level), Jointly prepared by the Curriculum Development Council and the Hong Kong Examination Authority 2002

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Syllabus

4.3 Ecology
4.3.1 Ecosystem
* the meaning of the terms : biosphere, biome, ecosystem, community and population.
* the concept of habitat and niche of an organism.
* an outline of population growth and the factors affecting it.
* an outline of biotic and abiotic factors in ONE local ecosystem and their effects on the distribution and abundance of organisms in that ecosystem.
* the use of an appropriate sampling method, such as sthe quadrat, line transect and belt transect, to study the distribution and abundance of organisms.


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Suggested Readings :

(1)Advanced-level Biology for Hong Kong , Book 1, by Y.K.Ho, Manhattan Press, pp.231-234
(2)A-level BIOLOGY, by W.D.Phillips and T.J.Chilton, Oxford University Press, pp.506-508
(3)Biology : Principles and Processes,by Roberts, Reiss and Monger, Nelson Press, pp.12-18
(4)Advanced Biology, Principles & applications, International Student Edition, by C.J.Clegg with D.G.Mackean, John Murray, pp.44
(5)Understanding Biology for Advanced Level, 4th Ed. by Glenn and Susan Toole, Stanley Thornes, pp.333-334


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Hierarchy of Ecology

According to the area it covered, the following terms are used in describing the area of ecology.

Biosphere (生 物 圈)

 In the study of ecology, the broadest area is called the biosphere . It describes the sphere on the Earth that is occupied by living things. The structure of the term is in contrast with the atmosphere, lithosphere and hydrosphere and form the 4 spheres of the Earth.


Biome (生 物 群 落 區 )

 In the whole biosphere, it can be easily found that there are several categories of environment. In each type of enviornment, there is specific type of lanscape, weather, and specific living things. These types of environments are called biome . One biome would gradually merge into another biome. There are eight types of biomes on the land.

(1) tundra (凍 原)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.506)
Tundra is confined mostly to the Northern Hemisphere where it forms a circumpolar hand separating the polar icecap from the coniferous forests to the south. The region is characterized by low temperatures and a short growing season. The loer ground levels are permanently frozen (permafrost) and only the hardiest plant forms can survive. Sphagnum moss, sedges, heather and lichens dominate the bogs and marshes which appear in the short summer and provide food for visiting caribou (馴 鹿), insects and migratory birds.

Picture source :
Discovery School
(2) Taiga (凍 原 針 葉 林)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.506)
Taiga is a Siberian word meaning "coniferous forest". Large areas of taiga stretch across North America, northern Europe and Asia and are a major source of comercial timber. The evergreen conifers shade the ground below and prevenet the development of ground shrubs. typical animals include hibernating or migratory animals such as bears, moose (塺), squirrels (松 鼠) and birds. There are far fewer species than in deciduous forests.

Picture source :
Discovery School
(3)Temperate deciduous forest (溫 帶 落 葉 林)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.506)
Temperate deciduous forest is found in areas with an annual rainfall of 75 - 150 cm distributed fairly evenly throughout the year. It is dominated by hardwood trees such as oak (橡 樹), beech (櫸 樹) or maple (楓 樹), which rise to 40 or 50 m. Their leaves shade the loer layers to some extent, but allow stable communities of shrubs and ground plants to develop. This is the vegetation natural to most of Britian, but much of the original forest has been cleared.


(4) Temperate evergreen woodland (chaparral) (溫 帶 常 綠 林)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.507)
Chaparral is found in mild temperate regions of the World with abundant winter rainfall and relatively dry summers, for example, in areas surounding the Mediterranean. It is characterized by evergreen thickets (灌 木 叢), small oaks (小 橡 樹) or eucalyptus trees and often includes man-made vineyards (葡 萄 園) or olive groves (橄 欖 樹).

Picture source :
Discovery School
(5) Temperate grassland (steppe) (溫 帶 草 原)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.507)
Temperate grassland is usually found in the central areas of continents where rainfall is 25 - 75 cm per year. The prairies of the western United States, and the grasslands of the USSR, Argentina, South Africa and Australia provide examples. The natural community is dominated by grasses and large herbivores such as bison. Burrowing mammals like ground squirrels and prairie dogs, and ground nesting birds are common. Much of this region has been exploited for agriculture both for growing cereal crops and for raising beef and dairy cattle.

Picture source :
Discovery School
(6) Tropical grassland (熱 帶 草 原)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.507)
A broad belt of tropical grassland or savannah stretches across Africa and other areas are found in Australia and South America. The annual rainfall may be as much as 125 cm, but a dry season prevents the development of forests. Grasses survive drought by means of extensive underground rhizome systems. The animals typical of these regions are herbivores such as antelope (羚 羊), zebra (班 馬) and wildebeest (牛 羚), and carnivores like lions and cheetahs (獵 豹).

Picture source :
Discovery School
(7) tropical rain forest (熱 帶 雨 林)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.507)
Tropical rain forest is found in areas close to the equator with an annual rainfall of 200 cm or more and comprises a spectacular variety of different organisms each with their own life-styles and adaptations. Most of the vegetation forms a dense layer, called the canopy layer, 25-35 m above ground level. This supports a large community of small animals and plants, including many epiphytes, that is, commensal or parasitic plants attached to the trunks and branches of trees. Tall trees extend their branches above the canopy. The forest floor is rich in decomposing vegetation and supports an enormous range of fungi and invertebrates. However, not much light penetrates the upper layers of the forest and the vegetation is dense only where there is a break in the canopy.

Picture source :
Discovery School
(8) Desert (沙 漠)，
(Ref : A-level Biology, by W.D. Phillips and T.J.Chilton, Oxford University Press, pp.508)
Deserts receive a reainfall of less than 25 cm per year. They support a very limited vegetation composed of xerophytic (droght-adapted) plants, such as cacti and succulents, and fast-growing annuals which appear and disappear with the infrequent rains. Almost all the animals supported by this meagre primary production avoid the extremes of climate by burrowing, feeding only at dusk and dawn.

Picture source :
Discovery School



Also, there are some aquatic biomes. Aquatic biomes are not included in the syllabus.
(9)Fresh water bodies, as the lakes and ponds,
(Ref: Biology : Principles and Processesses, by Roberts, Reiss and Monger, Nelson Press, pp. 17)
This is the area permanently flooded with fresh water. The community is related to the depth of the water.

(10)Seawater bodies, as the oceans,
Ocean is the area permanently flooded with seawater. It covers about 3/4 the surface of the Earth.

(11)Estuaries,
Estuaries are wetlands. They are the area in which freshwater rivers enter the saltwater sea or ocean. The characteristic is that the osmotic potential of the medium is not stable. Also, sometimes, water would dry up completely. So, both terrestrial animals, freshwater animals and marine animals can come. But the environment changes so fast that they would soon be killed by the change in environment.

(12)Freshwater wetland, as the shores of rivers and ponds
They are the wetlands that would be dried off some time in each year. This would be dependent on the supply of freshwater.

(13)Seawater wetland, as various kinds of seashores
(Ref: Biology : Principles and Processesses, by Roberts, Reiss and Monger, Nelson Press, pp. 18)
Seawater wetland is similar to the freshwater wetland, but it is different that the water has a low osmotic potential. Also, water would dry up some time in each day. The time of drying up would be dependent on the attraction of the moon. It is called the tides.




生 態 系 (ecosystem)

 A scosystem is a localized area having the conditions of a specific biome. As it is localized and smaller in size, it is convenient to conduct research in an ecosystem in order to know the biome. An ecosystem can be divided into the biotic component and the abiotic component. The biotic component is called the community. The abiotic component is called the habitat.


Habitat (生 境)

 Habitat is the abiotic component of an ecosystem. Therefore, the study of a habitat include the study of all physical and chemical factors in the ecosystem. If the area of study is very small, then, it can be called a microhabitat. As some plants grow in the cleft of the wall. Also, some insects are found in the same cleft. Then, the cleft of the wall can be called a microhabitat, because in the cleft there is specific physical and chemical conditions other than the open area.


Community (群 落)

 A community is the biotic component of an ecosystem. It is composed of the populations of various living organisms. As the community of a pond include the population of carps, population of frogs, and populations of various insects etc.


Population (種 群)

 A population is a group of living things of the same species. As a number of people constitute a population of human. A number of frogs constitute a population of frogs etc.


Niche (生 態 位)

 The niche of a specific species in an ecosystem is the profession of the species in the ecosystem. For example, the niche of bacteria is the decomposer in the soil etc.

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(15.02.2007)