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Aquarium has all the biotic and abiotic components of an ecosystem, so, aquarium is a complete ecosystem.

Of the incident solar radiation less than 50 percent of it is photo synthetically active radiation(PAR. Plants capture only 2-10 per cent of the PAR for gross primary productivity.

Beyond a certain depth in the ocean, sunlight is not able to penetrate. Due to which green plants cannot photosynthesise and thus, do not survive.

They are all detritivores i.e., decomposing organisms which feed on dead remains of plants and animals.

They are all detritivores, i.e., decomposing organisms which feed on dead remains of plants and animals.

Time taken is about 50-100 years in case of a grass land and about 100-200 years for a forest. Secondary succession.

1. Purify air and water

2. Mitigate drought and floods

3. Cycling of nutrients

4. Generate fertile soils

(a) Healthy ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services. The products of ecosystem Processes are named as ecosystem services. For examples, healthy forest ecosystem purifies air and water, minimize droughts and floods, cycle nutrients, generates fertile soils, provides wildlife habitat, maintains biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values. Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a healthy price tag. 

(b) Based on the nature of the habitat - whether it is water (or very wet areas) or it is on very dry areas - succession of plants is called hydrarch or xerarch, respectively.

Differences : Hydrarch succession takes place in wetter areas and the successional series progress from hydric to mesic conditions. As against this, xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions. 

Similarity : Both hydrarch and xerarch successions lead to medium water conditions (mesic), neither too dry (xeric) nor too wet (hydric).

FOREST ECOSYSTEM

Definition: It is a natural ecosystem consisting of dense growth of trees and wild animals.

Characteristic features of forest ecosystems:

1. Seasonality: In countries that have seasonal climates, forest ecosystems will change with the seasons.

2. Deciduous or evergreen: A forest may be deciduous (i.e. it sheds its leaves in winter) or evergreen (i.e. its leaves stay green and intact all the time), or it may be a mix of both deciduous and evergreen trees.

3. Different levels: Some forest ecosystems such as rain forests, feature several distinct levels – such as the forest floor, the lower canopy, the upper canopy and the tree tops.

4. Attractive to birds: Many bird species nest in tree tops and this makes forest ecosystems attractive to birds.

5. Attractive to insects: Many insects live in tree bark, leaf mulch or flowers and as such they find forest ecosystems very attractive places to make their homes.

Structure and Function of Forest Ecosystem

Abiotic: soil, sun light, temperature etc .

Biotic : forest trees, shrubs and animals

Structure:

Producer : Trees and shrubs

Consumer : Primary – elephants, deer etc.

Secondary – snakes, birds, lizards etc

Tertiary – lions, tigers etc

Decomposers : fungi, bacteria

Types of forest ecosystem: 

The forest type depends upon the abiotic factors such as climate and soil characteristics of a region. 

Forests in India can be broadly divided into 2 types.

1.Coniferous forests

2.Broadleaved forests

1.Coniferous Forests 

• Grow in the Himalayan mountain region 

• Temperature is low. 

• Have tall trees with needle-like leaves and downward sloping branches so that the snow can slip off the branches. 

• Have cones instead of seeds and are called gymnosperms.

2.Broadleaved forests. 

• Broadleaved forests have several types, such as :evergreen forests, deciduous forests, thorn forests, and mangrove forests. Broadleaved forests have large leaves of various shapes.

Evergreen Forests

• grow in the high rainfall areas of the Western Ghats, North Eastern and the Andaman and Nicobar islands.

• monsoon lasts for several months.

• Shed a few of their leaves throughout the year.

• No leafless phase.

• Only shade loving trees can grow in the ground layers as canopy overlap.

• Forest is rich in orchids and ferns abounds in animal life and is most rich in insect life.

Deciduous Forests

• are found in regions with a balanced amount of seasonal rainfall. • lasts for only few months.

• most of the forests in which Teak grow are of this type.

• trees shed their leaves during the winter and hot summer months and regain their fresh leaves just before the monsoon.

• Light can penetrate easily onto the forests floor.

Thorn Forests

• are found in the semi- arid regions.

• Trees are scattered and are surrounded by open grassy areas.

• can conserve water.

• Have long and fibrous roots to reach water at great depths.

• reduce loss of water

• some species have small leaves and some have thick waxy leaves. have thorns – protect plants from herbivores

Mangrove Forests

• grow along the coast especially in the river deltas.

• are able to grow in a mix and saline and fresh water, in muddy areas.

• have breathing roots. prevents soil erosion.

a. The sequential, gradual and predictable changes in the species composition in an area are called succession or ecological succession.

Ecological succession is of two types: 

i. Primary succession: It begins in areas where no living organisms ever existed. Therefore, the establishment of a biotic community is very slow, e.g., newly cooled lava, bare rock, newly created pond or reservoir. 

ii. Secondary succession: It begins in areas where natural biotic communities have been destroyed, e.g., abandoned farm lands, buried or cut forests. Since soil is available, it is a faster process.

b.

Earthworm is said to be 'friends‘ of farmer:

• Breakdown the complex organic matter.
• Loosening of the soil helps in aeration and entry of root.  

The decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients, called decomposition.

Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute the detritus. 

The process of decomposition completed in following steps: 

Fragmentation : Break down of detritus into smaller particles by detritivore (earthworm). 

Leaching: Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

Catabolism : Bacterial and fungal enzymes degrade detritus into simple inorganic substances. 

Humification: Accumulation of dark coloured amorphous substances called humus.

Secondary productivity is defined as the rate of formation of new organic matter by the consumer.

• A considerable amount of energy is utilized by plants in respiration. 
• Gross primary productivity minus respiration losses (R) is the net primary productivity. 
• GPP – R = NPP.

Net primary productivity is the available biomass for the consumption to heterotrophs (herbivore and decomposers).

The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. 

• It is expressed in terms of weight (g^-2) or energy (kcal m^-2) 
• The rate of biomass production is called productivity.

Gross primary productivity: (GPP) is the rate of production of organic matter during photosynthesis.

A group of organism irrespective of their size having same source of energy or similar food habit constitute a trophic level.

Different food chains are naturally interconnected e.g. a specific herbivore of one food chain may serve as food of carnivores of other food chains. Such interconnected matrix of food chains is called food web.

Grazing food chain: it extends from producers through herbivore to carnivore. 

Detritus food chain: Begins with dead organic matter (detritus) and pass through detritus feeding organism in soil to organisms feeding on detritus-feeders. 

In aquatic ecosystem GFC is the major conduit for energy flow. 

In terrestrial ecosystems a much larger fraction of energy flows through the detritus food chain than through GFC. 

Energy flow in ecosystem:

• Except for deep sea hydrothermal ecosystem, sun is the only source of energy for all ecosystems on earth.
• Less than 50% of incident solar radiation is photosynthetically active radiations. (PAR).
• Plants capture 2-10 % of PAR and used in photosynthesis. 
• All organisms depend on the producers, either directly or indirectly.
• Energy flow in the ecosystem is unidirectional i.e. energy transferred from producer to consumers.
• Energy transfer is not absolute, and spontaneous, unless energy is degraded it can not be transfer. When energy transferred from one trophic level to another, lot of energy lost in the form of heat to the environment.
• Only 10% of energy transferred from one trophic level to other.

Factor affects rate of decomposition:

• Decomposition is largely an oxygen-requiring process.
• Detritus rich in chitin and lignin has slow rate of decomposition. 
• Detritus rich in nitrogen and water-soluble substance like sugar has faster decomposition.
• Temperature and soil moisture are most important climatic factor that regulate decomposition.
• Warm and moist environment favor decomposition.

Humification: Accumulation of dark coloured amorphous substances called humus. 

Importance of humus: 

• Highly resistance to microbial action. 
• Undergo decomposition at an extremely slow rate.
• Being colloidal in nature, it serves as reservoir for nutrients. 
• Mineralization: The humus is further degraded by some microbes and release of inorganic nutrients occur. 

The process of decomposition completed in following steps:

Fragmentation : Break down of detritus into smaller particles by detritivore (earthworm). 

Leaching: Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

Catabolism : Bacterial and fungal enzymes degrade detritus into simple inorganic substances.

Humification: Accumulation of dark coloured amorphous substances called humus.

The decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients, called decomposition.