AL Bio notes Ecology - An Introduction P.7
Ecology --The Interrelationships between Organisms
and their Environment
E cologyis the scientific study of the i______between organisms and their environment.
The environment of an organism consists of both the phy___ (abiotic) and bio___ factors of the surrounding. /
I) The hierachical structure of the Biosphere
A) Habitat
A habitat is a pl___ with a particular set of physical (abiotic) factors in which suitably ada____ plants and animals live.
1. Aquatic habitats - places with water
a. Freshwater habitats - water with low salinity
i) Running water - water flows at high rate and contains high o_____ content e.g. streams.
ii) Standing water - water remains still (stagnant) and has comparatively low oxygen content e.g. paddy fields, ponds and reservoirs.
b. Marine habitats - water with high s______
i) Rocky shores- shores of bare rock surfaces and boulders, exposed to the splashing action of strong w____ e.g. Shek O, Big Wave Bay and many shores on the east coast of Hong Kong.
ii) Sandy shores - composed of sands formed from the broken fragments of boulders and are deposited in the shel_____ bays.
iii) Muddy shores - composed of silt and clay and usually with mang_____ growing on them. e.g Deep bay
2. Terrestrial habitats - places on land
a. Grasslands - mainly composed of gr_____ and small dicotyledons.
b. Woodlands – in HK, composed of tall trees which consist of both trop____ and temp____ species and include some coniferous forests that are deliberately planted.
c. Agricultural habitats - places used for growing rice and vege______.
d. Urban habitats - places with villages, towns and cities which change the natural environment
Habitats can be further subdivided into m____-habitats, each with its own particular conditions (micro-clim____). For example a rock pool in the rocky shore and the lower surface of a leaf are micro-habitats.
B Niche
The niche of an organism refers to all the r___ the organism plays in the ecosystem. The ecological niche of an organism means its entire way of life, including its habitat, behaviour, inter______with other species and particularly, its feeding habits. If habitat is analogous to an organism's 'address', niche is its 'profession'.
C. Population
Population is a group of individuals of the s____ species living together in a particular a___ and interb______ among themselves.
D. Community
All the pop______of plants and animals living together in a particular h_____and inter______with one another are regarded as a community.
E. Ecosystem (Ecological system)
It is a natural unit of l______and n___-l______components which interact to form a st____ system. There is a cy____ interchange of materials between the living and non-living components of an ecosystem.
The living components include all the living com______ and the non-living parts include all the phy_____ (abiotic) factors of the habitat.
e.g. a freshwater pond is an ecosystem. The non-living component of this ecosystem include ______. The living components include the ______..
F. Biome
The world is divided into broad cli_____ z____, each of which supports living communities typical of that climate. These large com______units are known as biomes.Biomes are named after their p_____ dominants, such as tropical rain forest, woodland, desert etc /
G. Biosphere
Biosphere is the entire space of the atmosphere, the land and water at the surface of the E____ which is occupied by l______organisms. It includes all the biomes and ecosystems on earth.
II) Factors making up the Physical Environment
A) Light -- Intensity, Duration & Quality
Varies with : sea____of the year, lat______, wea______conditions, and local topography.
a) Effect on plants
Leaf arrangement pattern (leaf mosaic): branches and leaves are spatially arranged to allow min______degree of overl______.
Sun plants : smaller leaves, higher compensation point, may possess xero______features.
shade plants : larger l______, lower com______point.
Phototrophism : g______response to directional light source.
Growth and dev__________affected by light. eg etiolation of seedling in the absence of light
b) Effects on animals :
Ultra-violet light is essential for the synthesis of vitamin___ in skin of birds and mammals. However heavy dose of UV light may cause s____ cancer.
Behaviour : noct_____ animals, they are active at night and have their eyes well adapted for dim light vision. eg. Owl with big, forward-facing eyes to enhance stereoscopic vision; they may also possess light reflecting layer behind the retina to enhance night vision. For diurnal animals, they are active in daytime.
c) Photoperiod
The number of daylight hours in a day is known as the photo______which may affect the sea_____ changes in responses or behaviour of certain plants and animals. e.g. flowering, seasonal migration (photoperiodism).
B) Wind
The drying effects of wind strongly affects the rate of tran______. It is also important for disper____ and pollin______of some plant species.
Distribution of organisms : Windward side / Leeward side of mountains may have very different fauna (a______) and flora (p______).
C) Temperature
Affect the r___ of enzyme reactions and meta______. Affect the act______and distri______of organisms as efficient metabolism is reststricted within nar____ temperature ranges.
Tolerance limits vary in different organisms and there is an opt_____ temperature for each species. water has a higher specific heat capacity-- therefore less temperature fluct______in aquatic than in terrestrial habitats.
effects on plants : rate of photo______and tran______, determine distribution of species of different t______limits.
effects on animals : poikilotherms become in______ when temperature falls outside the range of around 6ºC ---- 40 ºC. If unfavourable condition is seasonal or persists for long, the animal may enter a state of either hibernation (in winter) or aestivation (in summer).
Homeotherms are able to adapt to temperature changes by maintaining a con_____ body temperature. However, even some endothermic animals may mig______to warmer regions eg. birds, while others may h_______in cold weather. eg. bear, bat.
Q. Compare the temperature fluctuation in grassland compared to bare ground in a day, which one is more stable, can you suggest an explanation? What is the significance of a more stable temperature to the soil.
D) Gases and Dissolved gases
Oxygen is essential to the a______respiration of plants and animals. Since about 21% of air is composed of oxygen which in such great abundance will not greatly affect the terrestrial plants and animals.
However the amount of oxygen dissolved in different water bodies varies greatly according to the abio____ and bio___ conditions there.
a) A stream heavily poll____ with organic substances supports rapid bact_____ growth that will cause great reduction of dis_____ oxygen. As a result, the cle___ water species like stonefly larvae, may fly larvae and damsel fly larvae die while the tolerant species like chironomid larvae flourish in such poorly aerated water.
b) A f____ running stream has more dissolved oxygen than a stagnant pool.
E) Water
Water is an essential constituent of protoplasm. In order to survive, both aquatic and terrestrial plants and animals possess adaptations related with water.
a. The distribution of plants
i) Algae - They are restricted in water because of the absence of a waterproof cu______
ii) Mosses and ferns - They are bound to shady and m_____ areas since their sexual reproduction still require swim_____ sperms for fertilization.
iii) Higher plants (gymnosperms and angiosperms) - Their male gametes are well protected inside the poll___ grain, no external water is needed for fertilization.
They show varyng degree of adaptation to dry____ thus they are restricted in their distribution to different parts of the world.
· Tropical rain forests are found in the wet equatorial region.
· Coniferous forests are found in the dry temperate region.
· Hydrophytes live in water.
· Xerophytes live in very dry areas. e.g. cacti with spiny leaves to reduce water loss in the desert.
· Halophytes live in salty areas. e.g. mangrove plants
b. The distribution of animals
Animals that are not so well adapted to the desiccating conditions on land are restricted to moist areas:
· Earthworms are confined to damp burrows.
· Woodlice are restricted to damp places.
· Amphibia (frog) live near water to keep their skin moist and for external fertilization.
F) Salinity (salt concentration in water i.e. determines osmotic potential)
If organisms live in an environment where the o______potential is different from their own, they either lose or gain w_____ excessively that will threaten their life. They have to regulate their osmotic potential (osmo-regulation) in order to survive.
1. In fresh water
The low salinity causes a net __flux of water into the freshwater organisms which have to get rid of the ex____ water otherwise they may die due to the resulting dilution effect. e.g. Amoeba forms the contractile vacuole to remove the excess water by active transport. The turgor pressure exerted on the cell wall of the aquatic plants prevents the further entry of water.
2. In sea water
The high salinity of sea water causes a net ___flux of water out of the marine organisms which have to conserve water and replenish the loss. e.g. sharks retain urea in its blood to maintain a slightly hypertonic condition in its body compare to seawater.
3. In estuary
The salinity in the estuary is high when tide comes in. But the salinity is reduced when tide goes out and the water is diluted by the freshwater of the river. Estuarine organisms have high osmo-regulatory power in order to survive in such rapidly ch______ salinities of the habitat.
G) Soil
The soil provides an important link between the biotic and abiotic components of terrestrial ecosystems. It is composed of a mineral skeleton, org____ matter, a__, and w____. It also harbours the micro______responsible for de______and recycling of materials form dead remains to green plants.
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