BIOSPHERE, BIOMES AND ECOSYSTEMS

(Refer to Chapter 8 – Focus on Life Sciences: Grade 11, learning guide notes and slides)

A. IMPORTANT TERMINOLOGY Biosphere: Zone of air, land and water at the surface of the Earth in which living organisms are

found. Community: A group of organisms of different species living in a specific area at a specific time

and interacting with one another. Biome: One of the biosphere’s major communities, characterized in particular by certain

climatic conditions and particular types of plants and animals. Biotic organisms: Living organisms, including animals, plants, fungi, bacteria, viruses ect. Abiotic components: Non-living things in the environment e.g. light, gasses (air), water, soil,

temperature. Ecosystem: A biological community together with the abiotic environment, characterized by the

flow of energy and the cycling of inorganic nutrients. Biodiversity: Total number of species found in an area.

B. BIOSPHERE

The biosphere is the entire part of the earth that can maintain life. It includes the atmosphere, lithosphere and hydrosphere. The atmosphere is the lower part above the soil, which makes up a layer of gases,

airborne particles and water vapour that surrounds the earth. The most important gasses is nitrogen (78%), oxygen (21%) and carbon dioxide (0.03%)

The lithosphere includes the land masses made up of soil and rock. The lithosphere is important for the following reasons:

It provides the substrate for habitat for plants and animals. It is a source of minerals essential for growth and maintenance. It provides air and water to roots of plants and soil animals. It plays an important role in biogeochemical cycles

The hydrosphere refers to the part on earth that consist of water e.g. rivers, dams, oceans, lakes, ponds, streams.

Water covers ¾ of the earths surface. The hydrosphere is important for the following reasons:

It provides water which is most important constituent of all living organisms It provides the rainfall that supports terrestrial ecosystems. Ocean currents have enormous influence on climatic conditions in all parts of

the world.C. BIOMES

Terrestrial biomes Tundra Forests (coniferous- and deciduous- and tropical rain forests) Grasslands (savannas) Deserts Shrub lands

Aquatic biomes Wetlands Marshes Swamps Bogs Lakes Oceans Ocean currents Intertidal zones

BIOMES OF SOUTH AFRICA

South Africa has 8 biomes. A map of the different biomes is given, but can be seen in colour if you look at the following website: http://www.environment.gov.za/Enviro-Info/nat/biome.htm. When you discuss a specific biome, you have to refer to its, climate, soil and vegetation. The biomes found in S.A:

Succulent Karoo Savannas Fynbos Grasslands Forests Nama-Karoo Marine and Coastal Ecosystems Wetlands

Below is an example of how to discuss a specific biome. Do research on the remaining biomes and study their main characteristics

Succulent Karoo

The succulent Karoo is restricted to the year-round and winter rainfall areas and have the greatest summer aridity. This biome occurs mostly west of the western escarpment through the western belt of the Western Cape and inland towards the Little Karoo. This is the land of many spring flowers, which for a few weeks each year, draw large numbers of tourists from all over the world.

Succulent plant species with thick, fleshy leaves are plentiful here, the diversity of which is unparalleled anywhere else in the world. This, together with many geophytes (plants that survive by means of bulbs, tubers, etc. in times of unfavorable climatic conditions) and annual plants, makes the succulent Karoo unique and of international importance in terms of conservation. Examples of animals that occur here are the bat-eared fox (Otocyon megalotis), suricate (Suricata suricatta) and the common barking gecko (Ptenopus garrulus).

Savannas

Savannas are the wooded grasslands of the tropics and subtropics that account for 46% of the South African landscape. They are second only to tropical forests in terms of their contribution to terrestrial primary production. They are the basis of the livestock industry and the wildlife in these areas is a key tourist draw card.

The fact that the public are well aware of African savannas may be explained by the variety of large mammals found here. Large game species such as lion (Panthera leo), buffalo (Syncerus caffer) and elephant (Loxodonta africana) occur here. The large diversity of animals is associated with the rich plant diversity. A well-known tree species found in the Northern Province is the baobab (Adansonia digitata). Other species found here include the mopane (Colophospermum mopane), monkey-thorn (Acacia galpini) and knob-thorn (Acacia nigrescens). Savannnas also include valley bushveld, the veld type containing the greatest range of rainfall seasonality in South Africa. Fire is a crucial factor in the ecology of all savannas and is therefore a regular natural feature of this environment.

C. ABIOTIC AND BIOTIC FACTORS

The two main components which influence an organism in its natural habitat, are the abiotic (non-living) and biotic (living) components.

1. Abiotic components

The Abiotic components include the following: Temperature, water, soil, light, physiographic

factors.

a. Temperature

Temperature has a great effect on organisms and their choice of habitat is limited by the temperature which they can tolerate.

Many animals are cold blooded and cannot regulate their body temperatures. Day and night and summer and winter temperatures fluctuate a lot on land, to survive

each organism must be able to cope with these extremes of temperatures.

Adaptations of plants to temperature changes:

Seed germination: most seeds will germinate only after exposure to a period of low temperature.

Deciduous trees: shed their leaves in autumn to limit their metabolic processes, like photosynthesis and growth.

Annuals: Survive cold seasons as seeds Geophytes: are perennial plants with their resting buds below ground level, e.g.

bulbs, rhizomes, corms and tubers)

Adaptations of animals to temperature changes:

Exothermic animals (coldblooded animals) cannot maintain their own body temperature, therefore they can hibernate (winter sleep) during the cold months, or like lizards, they can lie on a rock in the sun to warm their bodies and barrow in the sand to cool down.

Endothermic animals (warm blood animals) maintain a constant body temperature and aren’t influenced by the fluctuations of the environmental temperature. But some of these animals hibernate during the cold winter months because food is scares.

Body covering: Thick fur, feathers and layers of body fat help mammals and birds to keep them warm.

Migration of birds: some birds fly to warmer parts of the world during the cold months, it is a seasonal movement.

Aestivation: During the hot dry summer months snail aestivate (summer sleep)

b. Water

It is the main component of living cells and is essential for all living organisms. 65% of the human body and 90% of plant bodies consist of water. The abundance of water, or the lack of it, has a striking effect on the ecosystem of a

region. The cyclic movement of water through ecosystems constitute the basis for the water

cycle. Adaptations of plants to meet their water requirements

Xerophytes: are plants that are adapted to live in very dry habitats, they are very resistant to draught and have to cope with shortage of water, high temperature and light intensity and dry, warm winds. How?

They absorb rapidly water when available (adventitious shallow roots/ roots grow deep into soil to reach water table/ leaves are spirally arranged and closely packed into a rosette to collect dew or rain)

They store water for use during periods of drought (roots/ leaves store water – they are thick and fleshy)

They reduce the loss of water by transpiration (older parts covered with cork/ leaves covered with wax/ cuticle to prevent water loss/ stomata is small, few or sunken/ leaves are modified to thorns)

They resist desiccation and wilting of plant parts (roots covered with cork layer/ young stems covered with wax or dead older leaves.)

Hydrophytes: are plants that live in water. They have to cope with too much water. These plants are adapted to aquatic life in the following way:

The leaf blade is large and flat and floats on water Numerous stomata to loose excess water through transpiration. Waxy cuticle cover upper part of leaf, water runs off. Airspaces make plant more buoyant.

Mesophytes: are plants that need an average normal supply of water. They avoid extreme moisture/ drought. Adaptations of animals to meet their water requirements:

Some animals burrow deeper to escape to drier upper soil like: earthworms.

Locust lay eggs in soil to hatch after first rains. The cuticle of the insects prevents desiccation. Some animals like springbok can survive without drinking water for

long periods. The kangaroo rat never drinks water, and get water from food.

c. Light

Light is the fundamental necessity. Plants need light for photosynthesis – to produce food. Food provide energy for animals. Adaptations of plants to light intensity:

Sun plants: these plants can tolerate a lot of light intensities. Shade tolerant plants: grow in shade, big leaves to absorb as much light possible

e.g. ferns. Phototropism: The growth movement is the tropic responses of shoots and

roots of plants to the stimulus of light. Shoots are positive phototropic and roots are negative phototropic.

Floral initiation: Some flowers open in high light intensity and some close in high

light intensity, this is due to their type of pollinators.

Adaptations of animals to light intensity: Many animals need light to find food, hiding places, nesting sites and mating

partners, and to escape their enemies. Day, night and twilight animals: Diurnal animals are active during the day, Nocturnal

animals are active during the night. Crepuscular animals are active mainly during twilight.

Pigmentation: Pigments (dark skin) absorb the ultraviolet light of the sun to prevent the deeper laying tissue from damaging.

Migration: Birds and some mammals move to different places during the autumn months when the daylight hours decrease.

Reproductive behaviour: The longer days of spring cause the reproductive organs of many animals to start growing, this gives rise to their breeding season.

d. Soil / edaphic factor

Soil is the habitat of most plants which are of importance to produce food. Soil has different pH. Most plant species prefer a neutral pH of 7. Acid soils are usually infertile because the acidity makes the mineral salts very soluble. Humus forms part of the topsoil, a dark coloured soil that consist of the remains of dead

organic matter. Humus is the fertile part of the soil. Three types of soil are found: Loam, clay and sand. Loam is the most fertile. The type of soil can be identified according to: particle size, stickiness, air content and

water-retaining ability. Soil contains the water and minerals needed by plants to grow in. Many animals have a habitat in the soil.

e. Physiographic factor Physiographic factors include the following: Aspect: refers to the position of an area in relation to the sun. North facing or south facing of a

mountain for instance, one side in dry and sunny and the other wet and cool. Slope: of a mountain can affect the rate of water run-off. Altitude: the height of a mountain will determine the amount of precipitation, solar radiation,

wind and shade that organisms in the ecosystem receive.

2. BIOTIC COMPONENTS OF AN ECOSYSTEM

The biotic component is that part of the total environment created by living, interacting organisms. The living components of an ecosystem consist of producers, consumers and decomposers.

a. Producers (plants)

The sun which is the primary source of energy, gives energy to the plants to produce food through photosynthesis.

Plants use the light, carbon dioxide, water and the green pigment chlorophyll in their leaves to produce sugars and oxygen.

These plants that produce food through photosynthesis are called producers. They are autotrophic organisms because they can manufacture their own food. Plants are the most numerous of all the biotic components. We learned in the abiotic component section how plants are adapted to different

environmental conditions. Plants that are not found naturally in an area are called invader plants and could

cause other endemic plants to die out, because the invader plants use a lot of water. Many plants have medicinal value. (Do a bit of research on medicinal plants found in

South Africa)

b. Consumers (Animals)

Animals are consumers because they are, directly/indirectly dependent on the food produced by the producers (plants), they consume this food.

Consumers therefore have a heterotrophic feeding method – they cannot make their own food and are dependent on the producers for nutrition.

In nature different types of consumers are found:

Primary consumers: They feed directly on producers – called herbivores.

Secondary consumers: They feed on the primary consumers – include carnivores (eat meat) and omnivores (eat meat and plants).

Tertiary consumers: They feed on primary and secondary consumers. They are also carnivores. Animals that feed on dead bodies of animals are called scavengers.

The number of producers are the most, the number of herbivores are less, the number of carnivores are less than the herbivores and the number of tertiary consumers are the least. This forms a ecological pyramid of the different trophic levels e.g. producers, primary consumers, secondary consumers, tertiary consumers and decomposers.

c. Decomposers

Decomposers are micro-organisms that break down complex organic matter into simple inorganic matter.

They obtain their energy for the decaying animals and plants. They are heterotrophic animals. We refer to them as saprophytic organisms. They include fungi and bacteria.

Today we mainly use biodegradable substances in our everyday life, these are substances that can be broken down by these decomposers, which replace the useful elements back

into the soil for plants to grow. Non-biodegradable substances e.g. plastic, glass ext. are harmful to the environment because it cannot be broken down into useful elements.

E. ENERGY FLOW WITHIN AN ENVIRONMENT

Every ecosystem is characterized by two fundamental phenomena: energy flow and chemical cycling. In this unit we will concentrate on energy flow within an ecosystem.

1. ENERGY FLOW

Energy flow begins when producers absorb solar energy for the process of photosynthesis. Energy flows through an ecosystem via photosynthesis because as organic nutrients pass

from one component of the ecosystem to another, such as when an herbivore eats a plant or a carnivore eats an herbivore, only a portion of the original amount of energy is transferred.

Eventually the energy dissipates into the environment as heat. Therefore, most ecosystems cannot exist without a continual supply of solar energy. Only about 10% of the food energy taken in by an herbivore is passed on to carnivores. A large portion goes to detritus feeders (decomposers) via defecation, excretion and death,

and a large portion is used for cellular respiration.

ENERGY FLOW IN AN ECOSYSTEM

ENERGY USAGE OF AN ORGANISM (ENERGY BALANCE)

2. TROPHIC LEVELS :

A trophic level is a level of nourishment with in a food web. The trophic levels are: producers (plants), primary consumers (herbivores), secondary

consumers (carnivores +/ omnivores), tertiary consumers (carnivores and scavengers) and decomposers (fungi and bacteria)

3. FOOD CHAINS

o The interaction of the autotrophic and heterotrophic components in which one organism consumes another, is called a food chain.

o In a food chain there is a continuous flow of energy from the sun, through the plants to the various animals.

o In a food chain there are always a producer and a consumer. o All food chains begin with a green plant and may consist of three to five links.

EXAMPLE OF TWO FOOD CHAINS IN AN ECOSYSTEM

4. FOOD WEB

Food web – consists of various food chains that interact with one another, therefore, interacting of energy flow within an ecosystem – it can be described as a diagram which shows trophic/feeding relationships)

5. FOOD PYRAMID

We distinguish between 3 types of food pyramids to describe a food chain.a. Number pyramid – Pyramid constructed to show the relationship between the

different numbers of each trophic level.b. Energy pyramid – Pyramid constructed to show the amount of energy received by

each trophic level.c. Biomass pyramid – Pyramid constructed to show the dry weight of each trophic level

in an ecosystem.

Some pyramids however have more herbivores than producers and are called inverted pyramids. E.g. The herbivores in the ocean weigh more than the phytoplankton (producers) that they consume; therefore the pyramid will look as follow:

F. NUTRIENT CYCLES

Unlike energy, the inorganic substances e.g. carbon, hydrogen, oxygen, nitrogen, phosphorus etc. within an ecosystem can be used over and over again. These substances are in limited supply, there is no inflow of new chemical elements as in the case of radiant energy and the amount of them remains fairly constant. For these reasons their cycling and re-use constitute an important part of ecosystems. The activities of producers, consumers and decomposers result in the recycling of these nutrients.

We will examine 4 nutrient cycles:

a. Water cycleb. Nitrogen cyclec. Carbon cycled. Oxygen cycle

a. Water cycle

The sun shining and the wind blowing over the oceans evaporate water from their vast exposed surfaces.

The water vapour produced in this way, moves into the atmosphere by evaporation. In the atmosphere the water remains as vapour, clouds and ice crystals.

It falls back as precipitation, mostly in the form of rain, hail, snow and dew. On land some water flows away in streams and rivers back to the oceans. Some water is absorbed by the topsoil for form hygroscopic-/capillary water. Some water filters through the topsoil into the subsoil to reach the water table – this

is called infiltration.\ Some water evaporates to reach the atmosphere again. Some water evaporates into the atmosphere from plants, plants looses water

through transpiration.

b. Nitrogen cycle

The main source of nitrogen is the atmosphere which consist of about 80% gaseous nitrogen.

This nitrogen is converted by soil and nodule bacteria and by lightning into ammonia and nitrates that can be used by primary producers.

The producers use the nitrates in the soil to produce protein for the consumers. Ammonifying bacteria convert urea into ammonia.

Nitrifying bacteria convert ammonia into nitrates which is returned to the soil. Denitrifying bacteria reduce nitrates and the nitrogen escapes back into the

atmosphere.

c. Carbon cycle

Carbon, in the form of carbon dioxide, is obtained from the atmosphere and used by photosynthetic green plants for the synthesis of organic compounds.

Most of the carbon dioxide returns to the atmosphere by activities such as respiration, decomposition and combustion.

d. Oxygen cycle

Discussion task

Do research on environmental issues that are linked to the nutrient cycle. Have a discussion on how environmental issues such as global warming are linked to the nutrient cycles listed.

Write an essay on these environmental issues, after the discussion, in order for you to understand the impact of environmental issues on the nutrient cycle.

An example of such an essay:

The carbon balance of the ecosystem has been highly influenced by global climate changes and CO2 content changes. Vegetation changes in the Alaska over the past decade has brought about important feedbacks on the region's biogeochemical cycles, mostly through altered rates of carbon and energy exchange between biosphere and atmosphere.

Nutrient cycling and fertilization studies in arctic ecosystems show that plant growth is strongly limited by nutrient availability. Such activity depends highly on decomposition, nitrogen mineralization, phosphorous availability, and controls on carbon and nutrient cycles, which in turn depend on temperature, moisture, decomposability of litter inputs, depth of thaw, etc.

The carbon cycle is strongly correlated with climate in the region, as well as the global climate dynamics. Because of the large amount of carbon present in northern soils and the presumed sensitivity of soil carbon accumulation or loss to climate change, northern ecosystems may be particularly important to global carbon balance in the future. Warmer soils could deepen the active layer and lead to the eventual loss of permafrost over much of the Arctic and the boreal forest. These changes could in turn alter arctic hydrology, drying the upper soil layers and increasing decomposition rates. As a result, much of the carbon now stored in the active soil layer and permafrost could be released to the atmosphere, thereby increasing CO2 emissions.