Introduction to Ecology A

Suggested Reading :
(1)Advanced-level Biology for Hong Kong, by Y.K. Ho, SNP Manhattan Press (H.K.) Ltd. Bk 1, pp. 33-59
(2)New Understanding BIOLOGY for Advanced Level, 4th ed., by Glenn and Susan Toole, Stanley Thornes pp.47, 50 - 66
(3)A-level Biology, by Phillips and Chilton, Oxford University Press pp. 37 - 45
(4)Biology : Principles and Processes, by Roberts, Reiss and Monger, Nelson Internatioinal Editions, pp. 151 - 171
(5)Advanced Biology principles and applications, ISE, by C.J.Clegg with D.G.Mackean, John Murray, pp.143 - 146, pp. 152 - 165.
(6)Biology, a functional approach, 2nd Ed., by M.B.V. Roberts, ELBS, Nelson, p.520-521.
(7)Biology, 7th Ed., by Claude A. Villee, W.B.Saunders Co. p. 833-857.

Ecology is the study of the relationship between the living things and their enviornment. The non-living components of the environment form the abiotic environment. While the living components form the biotic environment.

Hierarchy of the environment

The complex of the living things and non-living things is called an ecosystem. The ecosystem can be classified into the following levels.


The Earth is covered with several types of materials. And these materials form "spheres" covering the planet. These materials include the air, called the atmosphere; the water, called the hydrosphere; the rocks, called the lithosphere; and the living things, called the biosphere. They compose the four spheres on the Earth.


On the Earth, areas can be identified according to their distinct physical conditions and features. Areas of the same physical conditions and features are called biomes. As the physical conditions change gradually in distance, one biome would merge into another biome gradually. Different parts on the Earth would have the same physical conditions. Therefore, a specific biome would occur in different areas on the Earth.

There are 9 major terrestrial biomes on the Earth.

This is the biome in which the ground is permanently covered with ice, as the ice caps on the poles, at the peaks of high mountains and the glaciers. The boundary of the permafrost is called the ice line. In this biome the temperature is very low and not suitable for the growth of plants and inhabitated by animals. So, no or few living things can be found.

Tundra situates by the ice cap. The surface of the ground is covered with ice in winter, but the ice would melt 2 or 3 months in each year. Then, short grasses can grow. But a few centimeters beneath the top soil is the permanent frozen soil. In this biome, the total illumination is little and the duration of period with the air temperature above the freezing point is short. Therefore, few plants can accumulate enough nutrient to complete their life cycle. Also, few plants can complete their life cycles within this short term. So, living things in this biome is very limited. Only some mosses, sedges, heather, and lichens would occur in the swamps in summer. Also, they serve as food for caribou, insects or migrating birds.
Source of picture :
Discovery School
Taiga is the biome next to the tundra. It is the biome growing conifers and timbers. The bourder between the taiga and the tundra is also the boundary of trees. Therefore, this boundary is called the tree line.
In taiga, the air temperature is low and the winter is long. The ground is covered with ice in winter. The evergreen conifers cover the ground permanently. The sunlight reaching the ground is not enough for the growth of shrubs in beneath. Animals inhabiting here are the mooses and squirrels etc. Other animals adapting to this low temperature is few. Therefore, the biodiversity is less than in deciduous forests.

Source of picture :
Discovery School
(4)Temperate deciduous forest,
Temperate deciduous forests are widely spreaded on all the continents. The rainfall is between 70 - 150 mm annually. They are composed of some hard wood trees as oaks, beechs and maples of height of 40 - 50 meters. There is time for shrubs growing in beneath. But many of them had been removed for agricultural purposes.

(5)Temperate evergreen woodland (chaparral),
Temperate evergreen woodlands appear in the area with humid winter and arid summer, as the area around the Mediterranean Sea. Characteristic vegetation includes some thickets, orange, small oaks, grapes and olive etc. Cork is an important product.
Source of picture :
Discovery School
(6)Temperate grassland (steppe),
Temperate grasslands always located in the center of continents, as the center of Africa, Australia etc. The rainfall is between 25- 75 cm each year, as in the west of North America, Argentina, South Africa and Australia etc. Vegetation includes grasses and herbs. Fauna includes the squirrels and some cave-dwelling birds. Also, most of them had been transformed into agricultural fields.
Source of picture :
Discovery School
(7)Tropical grassland,
Tropical grasslands appear across Africa, Australia and south America. Anual rainfall may exceed 125 cm. The long arid season stops them from developing into forests. Herbal plants obtain water or store water with their subterranean parts. Fauna includes the herbaceous antelopes, zebras and wildebeests and the carnivorous lions and cheetahs etc.
Source of picture :
Discovery School
(8)Tropical rain forest,
Tropical rainforests are situated around the equator, and with the annual rainfall higher than 200 cm. The composition of tropical rainforests are very diverge. The environment can support a large amount of different organisms of different behaviors and different adaptations. Giant epiphytes may extend from the lower part to the upper part of the canopy. The amount of material cycling inside the tropical rainforest is huge. Therefore, large quantity of fungi and invertebrates can be supported. Canopy is dense, so, the amount of light penetrating is little. Only the part with less dense upper canopy can have ground surface vegetations.
Source of picture :
Discovery School
Desert is the most arid area on the Earth. The annual rainfall is lower than 25 cm. Only the extreme xerophytes, as cacti, can live here. Cacti survive with their long root system and water-storing stem parts. Other plants may bloom just after a heavy rainfall. Also, they complete their life cycle and disperse seeds before the ground water dries up. Fauna includes sand-burrowing species only, as scorpions. All of them are diurnal, because the temperature of the day time is too hot.
Source of picture :
Discovery School

There are 3 aquatic biomes as follow.

Ocean occupies the major part of the surface of the Earth. It is filled with seawater and the depth is high. The seawater contains a high concentration of salts, so, not all living things can live there. Living things not adapting to the low water potential of seawater cannot live here.
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Lake is the body of freshwater. The water potential of freshwater is high. Normally, they are swallow.
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Wetland includes swallow waters and flooded lands. They are very important enviornment for the exchange of materials, so the biodiversity is high. Also, wetland is the chief location for self-purification of environment. Thereore, conservation of wetland is highly noticed. Swallow lakes, rivers and estuaries are included.
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A ecosystem is a local part of the biome. for example, desert is a biome, Sahara desert, Gobi desert are ecosystems. They belong to the same biome of desert. All ecosystems of a biome have similar physical conditions, as climatic conditions and edaphic conditions, but may inhabited with different species of living things of the same adaptations. Therefore, a ecosystem can be divided into the nonliving part, abiotic component, and the living part, the biotic component. Energy flow and material cycling occur inside.


The habitat is the nonliving component of the ecosystem. It is the part directly interacting with living things.
In a big habitat there may be some small, localized parts. The physical conditions of these small localized parts may be very different from the outside big environment. Then, they are called the microhabitat. For example, a forest is a habitat. It has its specific physical and chemical environmental conditions. But beneath the bark, the environment would be quite different from the outside one. The humidity may be higher and illumination may be smaller. Then, this small environment is called a microhabitat. The fauna in the microhabitat would be quite different from that in the big environment. So, the study of the microhabitat would be a good choice in the study of ecology.


The community is the living part of the ecosystem. It includes all living things in the habitat. Interactions among species occur here.


A population is the aggregation of a species. So, the populations of all species in the habitat constitute the community of the habitat.


Niche is the profession of the living thing in a habitat. It includes how it lives and how it behaves. As the niche of bacteria is decomposer, and the niche of lions is predator etc. According to their roles, living things can be divided into producers, consumers, preys, predators, parasites, hosts, epiphytes, saprophytes, decomposers etc.