Structure of the Ecosystem:
Ecosystems are functional units of nature where living organisms interact with each other and the physical environment.
They can vary in size from small ponds or forests to large-scale systems like the biosphere.
Ecosystems can be categorized as terrestrial (land-based) or aquatic (water-based).
Examples of terrestrial ecosystems include forests, grasslands, and deserts, while aquatic ecosystems include ponds, lakes, wetlands, rivers, and estuaries.
Man-made ecosystems, such as crop fields and aquariums, can also exist.
Input, Transfer, and Output of Energy:
Ecosystems rely on the input of energy, primarily from the sun, which drives the process of photosynthesis in plants.
The energy captured by plants is transferred through the ecosystem in the form of food.
Energy flow occurs through the food chain or food web, where organisms consume other organisms.
Nutrients, such as carbon, nitrogen, and phosphorus, also cycle through the ecosystem, facilitating the growth and survival of organisms.
Energy and nutrients eventually leave the ecosystem through degradation and energy loss processes.
Relationships in Ecosystems:
Cycles: Ecosystems exhibit cyclic patterns in the movement of nutrients. For example, the carbon cycle involves the uptake of carbon dioxide by plants, its transfer to herbivores through consumption, and its release back into the atmosphere through respiration and decomposition.
Chains: A food chain represents the linear flow of energy as organisms are consumed by other organisms. For instance, a simple food chain in a forest ecosystem could be: plants → herbivores → carnivores.
Webs: Food webs are more complex than food chains and depict interconnected relationships among organisms in an ecosystem. They illustrate multiple feeding relationships and energy pathways. In a forest ecosystem, a food web could involve various plant species, herbivores, predators, and decomposers.
ECOSYSTEM – STRUCTURE, AND FUNCTION
Physical Structure and Species Composition:
The interaction of biotic (living) and abiotic (non-living) components results in the physical structure of an ecosystem.
Plant and animal species within an ecosystem determine its species composition.
The vertical distribution of different species in an ecosystem is called stratification. For example, trees occupy the top vertical strata in a forest, while shrubs and herbs/grasses occupy lower layers.
Components of the Ecosystem as a Unit:
The components of an ecosystem function as a unit in terms of productivity, decomposition, energy flow, and nutrient cycling.
Productivity: Autotrophic components, such as phytoplankton, algae, and plants, convert inorganic substances into organic material using solar energy.
Decomposition: Decomposers, including fungi, bacteria, and flagellates, break down dead matter, releasing nutrients for reuse by autotrophs.
Energy Flow: Energy flows unidirectionally through trophic levels, from autotrophs (producers) to heterotrophs (consumers).
Nutrient Cycling: Nutrients are recycled through the ecosystem, as decomposers break down organic matter and release nutrients for uptake by autotrophs.
Example of an Aquatic Ecosystem (Small Pond):
A pond is a self-sustainable unit and serves as a simple example of an aquatic ecosystem.
Abiotic Component: Water with dissolved inorganic and organic substances, along with soil deposits at the bottom of the pond.
Solar input and climatic conditions regulate the functioning of the pond.
Autotrophic Components: Phytoplankton, algae, and floating, submerged, and marginal plants found at the pond edges.
Consumers: Zooplankton, free-swimming organisms, and bottom-dwelling forms.
Decomposers: Fungi, bacteria, and flagellates abundant in the pond bottom.
The pond ecosystem performs all the functions of any ecosystem, including conversion of inorganic to organic material, consumption of autotrophs by heterotrophs, and decomposition and mineralization of dead matter for nutrient reuse.
Energy flows unidirectionally towards higher trophic levels, with some energy being dissipated and lost as heat to the environment.
PRODUCTIVITY
Nutrient Limitation: The availability of essential nutrients, particularly nitrogen and phosphorus, is often limited in the ocean. These nutrients are crucial for plant growth and primary productivity. In many regions of the ocean, the nutrient concentrations are relatively low, which restricts the growth of phytoplankton and other primary producers.
Light Limitation: Light penetration decreases with increasing water depth in the oceans. Sunlight can only penetrate the upper layers, limiting photosynthesis to the surface waters. This restricts the growth of primary producers to the euphotic zone, the uppermost layer where sufficient light is available. The majority of the ocean volume lies in the aphotic zone, where light levels are insufficient to support photosynthesis.
Temperature and Mixing: Ocean temperatures tend to be lower compared to many terrestrial environments. Cooler temperatures can limit the metabolic rates of organisms, including primary producers, thereby reducing productivity. Additionally, the mixing of water in the oceans is primarily driven by wind and ocean currents. This mixing is crucial for nutrient supply to the surface, and when it is limited, it can further constrain productivity.
Limited Availability of Carbon Dioxide: While carbon dioxide is essential for photosynthesis, its concentration in ocean water is relatively low compared to the atmosphere. The rate at which carbon dioxide can diffuse from the atmosphere into the ocean can limit the photosynthetic capacity of marine plants.
Biological Interactions: The presence of herbivores and grazing pressure can also impact primary productivity in the oceans. Grazing by zooplankton and other herbivores can control the abundance and growth of phytoplankton, thereby reducing overall productivity.
DECOMPOSITION
Decomposition:
Decomposition is the process by which complex organic matter is broken down into simpler inorganic substances such as carbon dioxide, water, and nutrients.
Dead plant remains (leaves, bark, flowers) and dead animal remains, including fecal matter, constitute detritus, which serves as the raw material for decomposition.
Decomposition plays a crucial role in nutrient recycling and organic matter turnover in ecosystems.
Steps in Decomposition:
Fragmentation: Detritivores, such as earthworms, break down detritus into smaller particles, increasing its surface area for further decomposition.
Leaching: Water-soluble inorganic nutrients in detritus dissolve and move down into the soil horizon, eventually precipitating as unavailable salts.
Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances, such as organic acids and smaller organic molecules.
Humification: Humification is the process of forming humus, a dark-colored amorphous substance that is highly resistant to microbial action. Humus serves as a nutrient reservoir and decomposes at an extremely slow rate.
Mineralization: Some microbes further degrade humus, leading to the release of inorganic nutrients, such as nitrogen, phosphorus, and minerals, through the process of mineralization.
Factors Influencing Decomposition:
Oxygen Requirement: Decomposition is largely an oxygen-requiring process known as aerobic decomposition. Anaerobic conditions can inhibit decomposition.
Chemical Composition of Detritus: The rate of decomposition is influenced by the chemical composition of detritus. Detritus rich in lignin and chitin (e.g., woody materials) decomposes slower, while detritus rich in nitrogen and water-soluble substances (e.g., sugars) decomposes faster.
Climatic Factors: Temperature and soil moisture are important climatic factors that regulate decomposition. Warm and moist environments generally favor decomposition, while low temperatures and anaerobic conditions can inhibit decomposition and result in the buildup of organic materials.
Energy Flow in Ecosystems:
Sun is the primary source of energy for all ecosystems on Earth, except for deep-sea hydrothermal ecosystems.
Less than 50% of incident solar radiation is photosynthetically active radiation (PAR) that plants can utilize for photosynthesis.
Plants capture only 2-10% of the PAR, and this small amount of energy sustains the entire living world.
Energy flows unidirectionally from the sun to producers (plants) and then to consumers.
Thermodynamics and Ecosystems:
The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. The flow of energy in ecosystems follows this law.
Ecosystems are not exempt from the second law of thermodynamics, which states that there is a universal tendency towards increasing disorderliness or entropy.
Ecosystems require a constant supply of energy to synthesize the molecules they need and counteract the tendency toward increasing disorder.
Producers and Consumers:
Green plants are the primary producers in terrestrial ecosystems, while various species like phytoplankton, algae, and higher plants serve as producers in aquatic ecosystems.
Consumers are organisms that depend on plants (producers) directly or indirectly for their food needs. They are heterotrophs.
Primary consumers are herbivores that feed directly on producers, while secondary consumers are animals that feed on primary consumers. Tertiary consumers can also exist in some ecosystems.
The Detritus food chain (DFC) starts with dead organic matter and involves decomposers, which are heterotrophic organisms (fungi and bacteria) that break down detritus into simple inorganic materials.
Food Chains and Trophic Levels:
Food chains are formed as organisms feed on other organisms, creating interdependencies in the ecosystem.
Organisms occupy specific trophic levels in the food chain based on their source of nutrition.
Trophic levels indicate the position of organisms in the food chain, with producers at the first trophic level, herbivores (primary consumers) at the second level, and carnivores (secondary consumers) at the third level.
Energy decreases as it moves up successive trophic levels due to the 10% law, where only 10% of energy is transferred from one trophic level to the next.
Detritus food chains (DFCs) are connected to grazing food chains (GFCs) in natural ecosystems, and the interconnections form food webs.
Limitations of Detritus Food Chains:
Unlike grazing food chains, detritus food chains do not have a limitation on the number of trophic levels.
The transfer of energy in detritus food chains is not restricted by the 10% law, allowing for a potentially larger number of trophic levels.
ECOLOGICAL PYRAMIDS
Ecological Pyramids:
Ecological pyramids represent the food or energy relationships between organisms at different trophic levels.
There are three types of ecological pyramids: pyramid of number, pyramid of biomass, and pyramid of energy.
Each pyramid has a broad base representing producers (first trophic level) and an apex representing tertiary or top-level consumers.
Ecological pyramids can be expressed in terms of number, biomass, or energy.
Considerations in Ecological Pyramids:
Calculations of energy content, biomass, or numbers must include all organisms at a specific trophic level to be accurate.
Organisms can occupy multiple trophic levels simultaneously, as trophic levels represent functional roles rather than specific species.
Human beings can function at multiple trophic levels in a food chain, depending on their dietary habits.
Patterns in Ecological Pyramids:
In most ecosystems, the pyramids of number, biomass, and energy are upright, with producers being more numerous and having greater biomass than herbivores, and herbivores having more biomass than carnivores.
However, there are exceptions to this general pattern. For example, counting the number of insects feeding on a big tree may result in an inverted pyramid of numbers when birds feeding on insects are also considered.
The pyramid of biomass in the sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton, which seems paradoxical.
Pyramid of Energy:
The pyramid of energy is always upright and can never be inverted because energy is lost as heat at each trophic level due to the second law of thermodynamics.
Each bar in the energy pyramid represents the amount of energy present at each trophic level in a given time or annually per unit area.
Limitations of Ecological Pyramids:
Ecological pyramids have limitations as they assume a simple food chain, which is rare in nature, and do not account for complex food webs.
They do not consider the same species belonging to multiple trophic levels or the role of saprophytes (decomposers) in the ecosystem, despite their importance.
Comments
Post a Comment