9.1 - Community and Ecosystem

In order to maintain the balance of the ecosystem, organisms need to interact with one another as well as with the non-living things.

Ecosystem

Community

Population

Species

Figure 1 - Habitat is the natural living place of an organism. A species refers to the group of similar organisms that live together, interbreed and produce offsprings. A population is formed when the same group of species live together in the same habitat. A community is the populations of all organisms of different species living together in the same habitat and interacting with one another. An ecosystem is formed when a number of communities live together in a habitat and interact with one another, including the non-living components (abiotic) such as water, air and soil.

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A niche is the role of an organism in an ecosystem which includes the behavior and interaction with the biotic and abiotic components present in the habitat. Niche can be classified into 2 types.

• Ecology niche , which is the role of a species in its surroundings.
• Species niche , is the way a species interacts with the biotic and abiotic components in its surroundings.

Biotic and Abiotic Components in an Ecosystem

Biotic and abiotic components are the major components in an ecosystem. Biotic components are organisms in an ecosystem that interact with other organisms. The abiotic components refer to the non-living components (physical and chemical characteristics) which affect the organisms present in an ecosystem.

• Abiotic components

  • pH value
  • Temperature
  • Light intensity
  • Topography
  • Microclimate
  • Air humidity

• Biotic components

  • Producers
  • Consumers
  • Decomposers

pH value

• pH value of the soil will affect the distribution of plants in a habitat. The soil is the natural habitat for millions of organisms such as earthworms, microorganisms and many others.
• Most of the organisms live in a neutral or almost neutral pH environment. Small changes in the pH value can affect the metabolic activities of organisms and reduce the fertility of the soil.

Temperature

• The surrounding temperature can also have an effect on the physiological activities of animals and plants.
• Changes in temperature can affect the metabolic activities of body as the reaction of enzyme is sensitive towards temperature changes.
• Most of the organisms have an optimum temperature at the range of 20°C to 40°C. However, there are some species which can live in extreme temperatures.
• For instance, polar bears live in Tundra where the temperature is -14°C whereas foxes can live in the desert where the temperature can exceed 45°C in the morning.

Light intensity

• Light intensity and the period of exposure to light can also have an impact on the distribution of organisms, especially green plants that can carry out photosynthesis.
• Tall trees in the tropical rainforests are exposed to high light intensity. Ini forms a canopy with lower light intensity underneath it. Only small plant such as ferns can survive under the canopy.
• Compared to regions with temperate climate where light intensity is rather low, coniferous forests have lower density of plants.
• Trees in the coniferous forests are also smaller in sizes and shorter.

Topography

• Topography is the physical characteristics of the surface of Earth which includes altitude, gradient and aspect.

• Topography can influence the air humidity, temperature and light intensity in the ecosystem.

• Altitude

  • At higher altitude , the relative humidity, atmospheric pressure and oxygen content will become lower.
  • Plants that live at different altitudes are different in types, sizes and density.
  • For example, pine trees (at higher altitude) are smaller compared to meranti trees (at lower altitude)

• Gradient

  • Steeper mountain slopes are more prone to erosion due to swift water movement.
  • The soil layer becomes thinner and drier.
  • As a result, this region has less growth of plants, except for short, thorny shrubs with small and pointed leaves.

• Asepect

  • Aspect is the direction where the wind blows and the rays of sunlight shines.
  • Mountain slopes that face the ocean will have more growth of plants compared to the side facing the inner land.
  • The slopes that face the ocean will also receive more rainwater. Hence, the density of plants is higher.

Microclimate

• Refers to the climate condition of a small area.
• For instance, the microclimate under a rock which is the habitat for millipedes.
• Depends on the temperature, humidity, light intensity, heat balance, atmospheric pressure, water evaporation and ability of the soil to retain water.

Air humidity

• Refers to the quantity of water vapor in the air.
• Most of the organisms live in areas where air humidity is high.
• Low air humidity will lead to loss of water through transpiration in plants.
• Consequently, absorption of water and mineral salts will increase.
• Transpiration can help to cool plants down in order to maintain an optimum temperature.

Autotrophic and Heterotrophic Nutrition

Nutrition is the way an organism obtains nutrients and energy through food. Nutrition can be classified into 2 types – autotrophic and heterotrophic. In Chapter 3, you have learnt about nutrition in plants. Now, let's take a look at the classification of organisms based on their nutritional habits.

• Autotrophic can be further divided into photoautotrophic, chemoautotrophic and saprotrophic.
• Heterotrophic can be divided into holozoic and parasitic.

1. Autotrophic

• Photoautotrophic
  • Organisms that are capable of synthesizing organic compounds from carbon dioxide gas and light energy.
  • Can produce own food through photosynthesis.
  • Example is green plants that have chlorophyll.

• Chemoautotrophic
  • Organisms that can synthesize organic compounds without light.
  • Generate energy through oxidation of non-organic substances such as hydrogen sulphide and ammonia via chemosynthesis.
  • Example is Nitrobacter sp.

• Saprotrophic
  • Saprophytic organisms obtain nutrients from dead and decaying organic substances.
  • Digestion happens outside the body of the organism before the nutrients are being absorbed by the saprotrophs.
  • Example is fungi.

2. Heterotrophic

• Holozoic
  • Organisms that consume and digest solid organic substances.
  • For example, humans and almost all animals are holozoic.

• Parasitic
  • Organisms that acquire nutrients from their hosts.
  • For instance, fleas and tapeworms absorb nutrients from humans (host).

Biotic Components According to Trophic Levels

Biotic components are living organisms that require energy to carry out metabolic activities. Humans and animals generate energy by consuming other organisms including plants. Therefore, all main source of energy comes from the sun. As explained previously, biotic components include producers, consumers and decomposers.

Energy Flow in the Food Chain

The feeding relationships between organisms in an ecosystem can be seen in the food chain. A food chain refers to the order of energy transfer from one trophic level to the next trophic level.

Figure 2 - The first trophic level in a food chain is the producers. Organisms on a higher trophic level will consume those organisms in a lower trophic level. Energy will then be transferred to the organisms that consume the other organisms. The energy is used to form new substances in the body.

Figure 3 - Most of the organisms can consume more than one type of organism. For instance, a bird can be a secondary consumer by eating a grasshopper (primary consumer). The bird can also act as a primary consumer by eating the paddy (producers). This creates a food web because the food chains formed are interconnected. The food web also begins with a producer that can perform photosynthesis and converts light energy into chemical energy to be stored in organs such as the leaves, roots and stems of plants.

Ecological Pyramids

The food chain and food web illustrate the feeding relationships between the organisms. When the trophic level increases, the number of organisms, biomass and the total energy in each trophic level will change. This can be clearly seen in ecological pyramids which can be divided into pyramid of numbers, pyramid of biomass and pyramid of energy.

Figure 4 - The pyramid of numbers. This shows the number of organisms present in each trophic level. The lowest trophic level has the highest number of organisms (producers). The higher the pyramid goes, the lower the number of organisms in each trophic level and the bigger the size of the organisms.

Figure 5 - The pyramid of biomass. This shows the total biomass per unit area of all organisms in every trophic level. This biomass is measured by using the dry mass. The value of the biomass shown above is the amount that can be supplied to the organisms in the next trophic level. The total biomass provided by the producers is the highest. The higher the pyramid goes, the lower the total biomass per unit area that can be supplied.

Figure 6 - The pyramid of energy. This illustrates the total amount of energy present in an ecosystem. The main source of energy comes from the sun. Green plants (producers) can undergo photosynthesis to produce chemical energy (food) which will be transferred to the body of the organisms that consume it (primary consumers). Most of the energy transferred (about 90%) is lost to the environment as heat, for living processes, excretion and discharge. Only a small amount of energy (10%) will be transferred to the next trophic level. Therefore, organisms on a lower trophic level have greater energy compared to those in the higher trophic level.

Types of Interaction among Biotic Components

In an ecosystem, all living things and non-living things interact with one another to live. The types of interactions between the biotic components include saprophytism, symbiosis, predation and competition. Competition can be further divided into 2 types – intraspecific competition and interspecific competition.

Symbiosis (interaction between different species)

• Mutualism

  • A type of interaction that gives benefits to both organisms.
  • For example, a myna gets its food (lice) from the body of a buffalo and the buffalo is free from lice.

• Commensalism

  • A type of interaction that gives benefits to one of the organisms only. The other organism does not suffer any kind of effects.
  • For instance, remora fish obtains food from the scraps of the shark's food while the shark is not affected at all.

• Parasitism

  • A type of interaction that benefits one of the organisms while the other suffers losses.
  • For instance, tapeworms that live in the intestines of humans absorb nutrients and causes the individual to suffer nutritional deficiency.

Saprophytism

• A type of interaction where an organism obtains food from dead or decaying organic substances.
• For example, mushrooms grow on dead tree trunk to obtain nutrients.

Predation

• An interaction where an organism (predator) feeds on the other organism (prey).
• For example, an owl (predator) hunts and catches rats (prey).

Competition

Competition (an interaction where organisms compete with one another for food, water, light or mates)

• Interspecific competition
  • Competition that involves different species.
  • For instance, plants compete to obtain sunlight.
• Intraspecific competition
  • Competition that involves the same species.
  • For instance, lions compete with one another to get mates.

Mangrove Ecosystem

Biotic and abiotic components in a mangrove ecosystem helps the adaptation of the mangrove trees in their habitats. Mangrove trees can be found in estuaries, that is at the mouth where the river meets the sea.

The adaptative features of mangrove trees

Leaves

• Thick cuticles and sunken stomata to reduce the rate of transpiration.
• Succulent leaves to store water.
• Hydathode helps to eliminate excess salt.
• Old leaves will fall off when too much salt is stored.

Pneumatophore roots

• Short root projecting from the surface of the soil for aeration.
• Helps in gaseous exchange through lenticels in water-submerged areas.
• For example, Avicennia sp.

Prop roots

• Branch out from the lower part of the stem of the tree.
• Anchored to the soil to support the trees and overcome strong winds and waves.
• For example, Rhizophora sp.

Buttress roots

• Thick structure that helps to widen the base of the tree.
• Provide support to the tree that grows on soft soil which borders with solid land.
• For instance, Bruguiera sp.

Seeds

• Viviparous seeds germinate and grow when they are still on the parent tree.
• Allows the seedlings to stick into the muddy soil and avoids them from being uprooted by the waves.

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An ecosystem can change due to the natural phenomena dan human activities. Eventually, this can result in death or migration of all the organisms. However, this deserted area will soon be inhabited by other living organisms which are called the pioneer species. Pioneer species are the first species to inhabit a particular area before any other species.

• Colonisation

  • Plants conquer a place previously uninhabited.
  • The plants reproduce and build a new colony at the place.

• Succession

  • Some dominant plant species in a habitat will be replaced by another species as time goes by.
  • The new species is known as the successor.

Figure 7 - Colonisation and Succession in mangrove trees area

Coastal zone

• Most exposed to big waves.
• Pioneer species that can be found in this zone are Avicennia sp. (Api-api tree) and Sonneratia sp. (mangrove apple).
• The roots branch out and pneumatophores help to trap mud and organic substances from the high tides.
• This causes the accumulation of mud over time. The soil becomes higher and denser.
• Rhizophora sp. Is the new successor and will replace the pioneer species.

Middle zone

• Situated along the river, closer to the estuaries.
• Rhizophora sp. (bakau minyak tree) can be found in this zone.
• Rhizophora sp. have tangled prop roots to trap mud and twigs as well as blocking water flow.
• This causes sedimentation. The river bank becomes higher and dry as it is less exposed to high tides.
• The soil is now not suitable for the growth of Rhizophora sp., being replaced by Bruguiera sp. (successor).

Inland zone

• Situated further into the land.
• The soil is higher, harder and only flows with seawater during high tides.
• Bruguiera sp. can be found in this zone.
• The buttress roots of Bruguiera sp. will trap more mud and silt.
• Sedimentation will form a new swamp that projects out towards the sea.
• The shore gets further away from the sea. The ground changes into a land. Trees like Nypa fruticans and Pandanus sp. start to grow and replace the Bruguiera sp.

The importance of the mangrove ecosystem

Protection zone

• The mangrove forests are the natural barriers that reduce the impact of waves and wind that reach the seashore.
• The mangrove forests are the protected site for small aquatic organisms such as the fishes, prawns and crabs.
• The mangrove forests also act as the preserved site where many species of birds can search for food.

Fishery resources

• Sea products are the source of income for fishermen.
• Conducive for fish rearing in floating cages for commercial species.

Forestry resources

• Mangrove woods can be used to make boats, fish traps and building frames.
• The woods can also be used to make handicrafts.
• The woods can be burnt to produce charcoal.

Food and medicine resources

• The fruits of Avicennia sp. can be eaten as vegetables.
• The nut of Avicennia sp. can be boiled and eaten. The flowers can produce honey.
• The fruits of Sonneratia sp. can be used in the making of drinks.
• The fruits of Nypa sp. can be eaten. The water from the fruits can be used to make vinegar and nira.
• The bark of Bruguiera sp. can be used to treat diarrhoea.