Paper : 12 Principles of Ecology
Module : 24 Natural and human modified ecosystem
Development Team
Paper Coordinator: Prof. D.K. Singh
Department of Zoology, University of Delhi Principal Investigator: Prof. Neeta Sehgal
Department of Zoology, University of Delhi
Content Writer: Dr. Kapinder and Dr. Haren Ram Chiary Kirori Mal College, University of Delhi
Content Reviewer: Prof. K.S. Rao
Department of Botany, University of Delhi Co-Principal Investigator: Prof. D.K. Singh
Department of Zoology, University of Delhi
Description of Module
Subject Name ZOOLOGY
Paper Name Zool 12 Principles of Ecology Module Name/Title Ecosystem
Module Id M24 Natural and Human modified Ecosystem
Keywords Ecosystem, natural ecosystem, human modified ecosystem, cropland, agro ecosystem, terrestrial ecosystem, marine ecosystem.
Contents:
1. Learning Outcomes 2. Introduction
3. Types of ecosystems 4. Natural ecosystems 4.1. Terrestrial ecosystems 4.1.1. Forest ecosystem:
4.1.2. Grassland ecosystem 4.1.3. Desert ecosystem 4.2. Aquatic ecosystems 4.2.1. Fresh water ecosystems 4.2.2. Marine ecosystem 4.2.3. Estuarine ecosystem 5. Human modified ecosystem 5.1. Cropland as an example
1. Learning Outcomes
After studying this module, you shall be able to:
Understand the concept of ecosystem.
Learn different kinds of ecosystem present on earth.
Know different types of natural ecosystem.
Understand the differences between natural and artificial ecosystem.
2. Introduction
Ecosystem is a functional unit in which all living organism and non living component of the environment are linked together through energy flow and nutrient cycle. The term ecosystem was coined by A.G. Tansley in 1935. The word ecosystem is derived from Eco + system,
„Eco‟ means Biotic + Abiotic and „System‟ means dynamic functional attributes. It involves energy and cycling of nutrients between biotic and abiotic components. Thus, the Ecosystem is unique to ecology as sustained life on earth is a characteristic of ecosystem not of the individual or population.
An ecosystem can be small (Pond) or large (forest, desert etc). These unit ecosystems are separated from each other with time and space, but functionally they are linked together to form a single whole, the biosphere. The functional pattern of ecosystem is very important because all of its components are dynamic in one or the other way and are responsible for creation of unique relation of man-environment as well as habitat, different from other region. The major functions of the ecosystem are:
It regulate flow rate of materials including nutrient cycle.
It regulates energy flow through production and respiration in the living organisms.
It regulates the diversity of living organisms which in turn is responsible for its own stability.
It maintains the limit of tolerance for each organism in the ecosystem.
It controls alteration of any one component because it is holocoenotic in which one component affects the other components.
3. Types of ecosystems
On the earth, there are large numbers of macro and micro ecosystems which unite together as a single unit to form biosphere. Identification of micro ecosystem will not only help in understanding the ecosystem but also helpful in regional development and planning.
On the basis of the differences in climate, habitat, natural vegetation, soil and water bodies, different ecosystems can be identified. Broadly, biosphere can be categorized into two major types- terrestrial and aquatic ecosystem and each is further divided into three subtypes on the basis of habitat.
4. Natural ecosystem
These ecosystems are formed and maintained in natural ways without any major interference by humans. They are further classified on the basis of kind of habitats as:
4.1: Terrestrial ecosystems:
It consists of Grassland, Savana, Taiga, Tundra, Desert and forests ecosystems (figure 1).
The main characteristic features of terrestrial ecosystem are:
i) Moisture content in the air becomes a limiting factor for terrestrial organisms as they are more prone to dehydration.
ii) Extremes of temperature are more prominent in terrestrial ecosystem.
iii) There is uniform distribution of oxygen and carbon dioxide due to rapid circulation of air in the atmosphere.
Figure.1. Terrestrial forest ecosystem 4.1.1: Forest ecosystem:
Forest ecosystem is predominated by trees which are interspersed by different species of herbs, shrubs, climbers and lichens. Forest occupy around 40% of land area all over the world whereas, India has forest cover of less than 19% of its total land area. The animal species consists of different species of insects (ants, flies, mosquitoes and beetles), herbivores (elephants, deer, rabbit, fruit bats, neelgai, monkey, squirrel and moles), carnivores (snake, lizards, wolves, fox, tiger and lion) and decomposers (bacteria and fungi).
4.1.2: Grassland ecosystem:
It is dominated by grasses but some trees and shrubs are also found. Grasslands develop in the area where annual rainfall is around 250-270 mm, evaporation rate is higher and there is seasonal and annual drought (figure 2).
Figure.2: Grassland ecosystem.
Grassland covers around 24% of total land area around the world. The fauna consists of herbivores (deer, buffalo, cow, rabbit, mouse, insects and termites), carnivores (snake, lizards, fox, wolves, birds, lion, tiger and jackal) and decomposers (bacteria and fungi).
4.1.3: Desert ecosystem:
This type of ecosystem is found in the area where average rainfall is below 250 mm and here precipitation is lower than evaporation. Due to scarcity of water and higher temperature, the biota is much varied but is poorly represented. Three life forms of plants can be found:
i) Annual plants which avoid drought by growing only when sufficient moisture is present.
ii) Succulents: The plants that can store water.
iii) Desert shrubs that are adapted to dry conditions.
Figure.3: Desert ecosystem.
The animal species represented by desert ecosystem includes insects, nocturnal rodents, reptiles (snakes and lizards), camel and few species of thermophilic fungi and bacteria.
4.2: Aquatic ecosystems:
Aquatic ecosystem is associated with the organisms that are present in the water bodies.
Aquatic organisms have same basic requirement as needed by terrestrial organisms for the process of growth, development and reproduction. The difference is in the form in which the resources are available to the organisms. For example, carbon dioxide and oxygen are present as gaseous state in the terrestrial ecosystem whereas, in aquatic ecosystem they are present in the water in dissolved form. Depending upon nature and quality of water, the aquatic ecosystem is further divided into two types:
4.2.1: Fresh water ecosystems:
They occupy small portion of earth‟s surface but are important to humans for providing drinking water, for industrial use as well as they also act as life support for terrestrial animals.
This type of ecosystem is further categorized as:
i) Lotic ecosystem: It consists of ecosystem of running water as stream or river ecosystem.
ii) Lentic ecosystem: It consists of ecosystem of standing water such as lake or pond ecosystem
Water containing little or no chlorine is called freshwater. The Venice system classifies brackish waters by their percentage of chlorine content. Freshwater contains 0.03 percent or less of chlorine. The freshwater systems are as follow:
a) Lake and Ponds b) Rivers and Streams
c) Wetlands such as Bogs, Marshes, Fens, Shrub-Carr and Swamps.
These systems are fed by water and nutrients leaching from surrounding catchments area.
a) Lakes and Ponds:
Lakes and ponds have very little or no water current, allowing the water body to separate out into layers depending upon the temperature and chemical composition (figure 4). The illuminated, warm water is called the epilimnion. The cooler water below, the metalimnion, becomes colder with depth. For every 1m depth, the temperature declines by 1°C. When the temperature of the water reaches 4°C, has the greatest density, it settles as a layer at the bottom called the hypolimnion.
Figure.4: Lake Ecosystem.
In shallower lakes, the stratification persists during the summer when surface waters are warm. On the basis of depth of water and types of flora and fauna, there may be three zones in a lake or pond.
i) Littoral zone: It is the shallow water zone which is generally occupied by rooted plants.
ii) Limnetic zone: It is an open water zone where effective penetration of light takes place and generally occupied by smaller organisms such as rotifers, crustaceans, insects and their larval stage and algae.
iii) Profundal zone: It is the deep water zone where light penetration is negligible. This zone is associated with various organisms such as crabs, snails and mussels.
On the basis of geology and substrate of the surrounding catchment, lakes can be categorized as eutrophic lake which is rich in nutrients and oligotrophic lake which is poor in nutrients.
The process of eutrophication in lake can also occurs by addition of organic and inorganic pollutants released by industries.
b) Rivers and Streams:
Rivers and streams differ greatly on the basis of their size. They also vary along their length, from their source in the upland and the sea. In general, as the mouth of a river is approached:
i) The velocity of water flow decreases, it results in less turbulence in water and there is gradual decrease in oxygen level of water.
ii) The volume of water gradually increases as the river passes through its catchments.
iii) There is gradual decrease in energy of the river.
iv) Suspended materials are continuously deposited, as a result the river bed becomes composed of finer particles and eventually silt.
v) The river bed becomes less steep as the water erodes a broader channel.
Streams are high in the catchment, that are unpolluted and will support caddis fly (Trichoptera) and blackfly (Simulium spp.) larvae feeding fine organic particles. The water will be too turbulent and poor in nutrients for all aquatic mosses, liverworts and algae. The Planktonic communities consist of algae, rotifers, photosynthetic bacteria and crustaceans that develop downstream where there is increase in volume of flowing water and decreased water current. Animals may also be present which includes different species of fish, reptiles, birds and mammals.
c) Wetland ecosystems:
Wetlands range all along a gradient from permanently flooded area to periodically saturated soil and support different hydrophytic plants species at sometime during the growing season (figure 5).
Figure.5: Wetland Ecosystem.
Hydrophytic plants are adapted to grow in water or on soil that is periodically anaerobic because of excess amount of water. Fresh water wetlands can be divided into the following types:
i) Bogs: Bogs are the areas having waterlogged soil with spongy covering of various mosses species. These are the landforms which are characterized by the accumulation of peat filled depressions in northern latitude especially glaciated regions.
ii) Marshes: Marsh is a wetland that is dominated by grass like plant species (graminoids).
Marsh is generally found as a zone around a lake or pond or alongside a river. However, it may also occur far away from any water bodies in areas where the water table is high. Marsh vegetation consists of cattails, reeds, bulrushes, spike rushes and wild rice. Deep marshes are bordered by emergent vegetation such as pondweed, naiads, wild celery, and water lily.
iii) Fen: A fen is an “alkaline bog”, basically a mineral rich peat land. Usually, fens occur at the base of slopes in the path of mineral charged ground water that results in a near neutral to slightly alkaline pH. Swamp milkweed, marsh bellflower, kalm‟s lobelia, grass of Parnassus and dwarf birch are common plants found in fen.
iv) Shrub-Carr: Shrub- Carr is the wetland variety of thicket, shrubby vegetation which may invade marshes, fens or bogs. Dogwoods, willows, buttonbush and birches are the most common types of shrubs in marsh.
v) Swamp: A swamp is a wooded wetland. Swamps may be:
i) Shrub Swamps: It is the swamp with waterlogged soil, often covered with 15 cm or more of water. Alder, willow, buttonbush and dogwoods are common vegetation. These also act as nesting and feeding areas for ducks to a limited extent.
ii) Wood Swamp: It is the swamp with waterlogged soil, often covered with 0.3 m of water, found along sluggish streams, flat uplands and shallow lake basins. Tamarack, arborvitae, spruce, red maple, silver maple, water oak, over cup oak, tupelo swamp, black gum and cypress are commonly found plants.
4.2.2: Marine Ecosystem:
These are gigantic reservoir of water occupying around 70% of earth surface. Marine ecosystem differs from fresh water ecosystem in having high salt concentration as well as it is deep and continuous, and there is continuous circulation of water. Most of marine water have temperature of 2 to 3 degree Celsius, devoid of light and 62% of water is under high pressure (>100 atm). The marine ecosystem consists of smaller autotrophs such as planktons and neutons, to larger animals like giant squids, fish, whales and much greater diversity of autotrophs and heterotrophs. The marine ecosystems include shallow water ecosystem (ecosystem along coastal line tidal zone), estuarine ecosystem (ecosystem of river mouth) and deep sea ecosystem (ecosystem beyond coast line) (figure 6).
Figure.6: Marine ecosystem Marine or Oceanic ecosystems include:
a) Open oceans b) Continental shelves
c) Inter-tidal zone and coral reef d) Salt marsh
a) Open Ocean: Ocean water can be reached up to 10 km deep and much of the water is devoid of light, poor in nutrients and unproductive. Generally, light can penetrate about 150 meters producing a surface zone called as photic zone where autotrophs are present and can perform the process of photosynthesis. The phytoplanktons presents in this ecosystem includes cyanobacteria, microscopic algae, diatoms and flagellates. These phytoplanktons provide food and support large numbers of zooplankton which includes various larval stages of marine and intertidal invertebrates. The Planktonic organisms are not able to control their movement but those organisms that are able to swim are part of the nektons. Below the photic zone, various carnivorous and detritivorous animals are found that feeds on the communities present in photic zones. The light penetration and productivity of sea gradually declines with increase in depth. Bottom or benthic fauna is sparse except in regions of hydrothermal vents.
Three hundred thermal vent species have been described, from sulfur bacteria to limpets, Tubeworms and fishes are unique to this habitat.
b) Continental shelves: Continental shelves support some of the most productive marine ecosystems, particularly in areas of upwelling where water currents bring nutrients from the deep to the surface water. Here kelp forests are found which are formed from brown algae, such as Laminaria spp. This anchors itself to the substrate and can grow up to a height of 50- 100m or more. The shelf benthos supports diverse species of animals such as mollusks, annelid (Polychaete worms), sea squids, porifera, bryozoans, sea spiders, crustaceans, echinoderms and different species of fish population.
c) Intertidal zone and Coral reefs: Intertidal rocky shores are dominated by algae. Sand beaches provide an unstable, abrasive and nutrient poor substrate that is inhabited by filter feeding burrowing animals which forms the food for different wading birds.
Diverse coral reef communities also occur in warm and shallow water zone. Corals are colonials‟ animals, belong to phylum cnidaria (eg. Hydrozoans) which produce complex calcareous skeletons made up of calcium carbonate. These corals provide habitat for various algae, invertebrates and carnivorous fishes.
d) Salt Marsh: Salt marsh occurs in shattered areas, protected from wave action and provides a stable substrate for colonization by salt tolerant higher plant.
4.2.3: Estuarine ecosystem:
Water of most streams and rivers ultimately drain into the sea and the place where this fresh water meets salt water is called an estuary. Estuaries generally develop two important types of ecosystems:
i) Mud flats
ii) Mangrove forests
i) Mud flats: Mud flats tend to retain organic matter deposited by the tide because of their small particle size. Estuarine silts consist of river sediments which are very rich in organic matter. The lack of oxygen restricts the survival of organisms in these muds and silts. But the
ii) Mangrove Forest: Mangrove forests replace salt marshes in warmer climates and develop on anoxic mud. They cover 60% to 70% of the coastline of tropical regions. The dominant plants have shallow and widely spreading roots which emerge from the trunk above ground and act as props. Many species have root extensions that absorb oxygen from the air. They are known as pneumatophores. Genus like Rhizophora dominates the mangrove ecosystems.
These forests are rich with fauna having unique combination of terrestrial and marine life.
Fiddler crabs and tropical land crabs burrow into the mud during low tide. In the Indo- Malaysian mangrove forests mud skippers (Periophthalmus) are found. These are fish that live in burrows in the mud and are able to crawl about on top of it like amphibians.
5. Human modified ecosystems
The natural ecosystems operate as self regulating systems without much direct interference and manipulation by man (figure 7). However in nature there is another engineered ecosystem in which man is very much involved and steer its operation. Among man made ecosystems, agro ecosystems are extensively prevalent in all parts of the world in various forms.
Figure.7: Human modified ecosystem (Crop land).
Some of the agro ecosystems are highly developed by modern scientific inputs as intensive cultivation practices, while some are still on traditional forms, practiced usually for subsistence needs. To simplify, Agro-ecosystem can be broadly classified into three types:
1) Pre-industrial agriculture: This type of agriculture is self- sufficient. It requires more manpower and use of animals for culturing the crops. The harvested crop is sufficient to farmer and its family or it can be sold in the local markets. There is no excess production of crop for export.
2) Conventional or Industrial agriculture: This type of agriculture is done by using machines and various chemicals such as insecticides, herbicides and fertilizers. The harvested crop is more than the need of farmers and can be exported and traded.
3) Alternative agriculture: It is based on sustainable agriculture with small use of chemicals. It stresses mainly on sustaining crop yield and benefit while promoting the lower usages of fuel, insecticide, fertilizers and herbicides.
Around 60% of the field available for agriculture is used as preindustrial agriculture in which most of them are present in Asia, Africa and other developing countries. The industrial agriculture is beneficial and greatly in use because it provides sufficient food and fibers for huge growing human population (more than 6 billions). However, it has certain side effects, firstly, it adversely affects the smaller farmers, which results in their migration towards cities and they became consumer, secondly, it greatly increase nonpoint pollution and soil loss. To overcome this problem, new agriculture system called sustainable agriculture is emerging which has greater future impact on future agriculture system.
Agro ecosystems may be present as monocultures (one major crop), mixed or multiple cropping of annuals and as agro forestry systems. The agro forestry is farming of woody perennials plants as predominant component along with agriculture or animal husbandry in various spatial and temporal arrangements. It is usually rich in biodiversity component and
Agricultural lands, gardens, parks, horticultural gardens even cities, towns, villages, industrial and mining areas are other examples of man–made ecosystems. The space capsule which lasts for limited period is also an artificial ecosystem. Unlike natural ecosystems, these man–
made ecosystems have weaker self regulatory mechanisms and depend on regular external input for their very existence.
These artificial ecosystems are maintained to obtain food, cloth, timber, medicines and other useful products. In fact man is to be blamed for replacement of natural ecosystems. To secure maximum production man makes much planned manipulations in the physico-chemical environment.
Best example of artificial ecosystem is cropland ecosystem in which man frequently optimizes the soil, climatic and other environmental conditions to secure maximum production. These include addition of fertilizers to soil, use of chemical for disease control and proper irrigation practices. Thus, a cropland ecosystem is aimed primarily to grow a single species of one‟s choice. The dominant vegetation of this ecosystem is the economically important crop species like wheat, paddy, jowar, maize, sugarcane, tea and coffee under most suitable conditions of their growth and yield. It is generally argued that in a natural ecosystem, the nature maximizes for maximum production, whereas in the artificial ecosystem man maximizes for net production. The biotic components of such ecosystems vary with agro climatic conditions and the societal set up of the people practicing it. The abiotic components of cropland ecosystem are similar to natural ecosystems including climatic conditions, organic and mineral contents of the soil but these are frequently monitored and are maintained at a certain level to provide maximum production. Apart from the commercial crop, the biotic ecosystem of this component includes several types of animals like birds, rabbits, rat and other smaller reptiles and insects, the decomposition of dead organic matter of plants and animals by fungi and bacteria make the minerals available again.
In a cropland ecosystem, there is not necessarily an increase in the total dry matter production of the whole plant, but generally most of the production goes into grain and less into leaves stem and root. Thus, in agriculture, there is an objective to achieve high rate of production (P)
of readily harvestable products with little standing crop (B) left in the field for accumulation or there is high P/B efficiency. On the other hand, natural ecosystem follow just reverse ie high B/P efficiency where standing crop is generally accumulated to its maximum. In 1959, Odum classified artificial ecosystem on the basis of photosynthesis respiration ratio (P/R) into three types.
a) Stabilized ecosystem: This type of ecosystem is formed when photosynthesis /Respiration ratio is almost one.
b) Autotrophic ecosystem: This type of ecosystem is formed when photosynthesis /Respiration ratio is more than one.
c) Heterotrophic ecosystem: This type of ecosystem is formed when photosynthesis /Respiration ratio is less than one.
5.1: Example of cropland:
The cropland ecosystem can be better understood by simple example of maize crop (figure8).
The following are the main component of maize cropland: Biotic components:
Producers: The dominant plant species is Zea mays. Besides maize, a number of weeds like Cynodon dactylon, Launaea nudicaulis, Euphorbia hirta, Cyperus rotundas, Digitaria spp and Alysicarpus spp also contribute to the primary production of the field.
Consumers:
Primary consumers:
These are the herbivores represented by a variety of animals, include chiefly the insects as aphids, thrips and beetles which feed and lay their eggs on maize leaves, flower and fruits.
Secondary consumers:
These are carnivores like frogs and smaller birds.
Tertiary consumers:
It includes snakes and hawks which feed on secondary consumers.
Decomposers:
These are microbes present in the soil as well as air that decompose the dead organic matter of plants and animals. These are chiefly bacteria, actinomycetes and fungi which are responsible for decay, decomposition and humification, making the mineral available again to the producers.
6. Summary
Ecosystem is unique to ecology as sustained life on earth is a characteristic of the ecosystem and not the individual or population.
An ecosystem can be small or large. These unit ecosystems are separated from each other with time and space, but functionally they are linked together to form a single whole unit, biosphere.
On the basis of the differences in climate, habitat, natural vegetation, soil and water bodies, different ecosystems can be identified.
Natural ecosystems are formed and maintained in natural ways without any major interference by humans.
They are further classified as Terrestrial ecosystem which consists of Grassland, Desert and forests ecosystems.
Aquatic ecosystem is associated with those organisms which live in the water bodies.
Depending upon nature and quality of water, the aquatic ecosystem is further divided into fresh water and marine water ecosystems.
Fresh water ecosystem occupy small portion of earth‟s surface and it is further categorized as Lotic ecosystem having running water and Lentic ecosystem consists of ecosystem of standing water.
Marine Ecosystem is gigantic reservoir of water occupying around 70% earth surface.
Marine ecosystem differs from fresh water ecosystem in having high salt concentration as well as it is deep and there is continuous circulation of water.
Artificial ecosystem or manmade ecosystem is an engineered ecosystem in which man is very much involved and steer its operation.
Among man made ecosystems, agro ecosystems are extensively prevalent in all parts of the world in various forms.
Agricultural lands, gardens, parks, horticultural gardens and even cities, towns, villages, industrial and mining areas are other examples of man–made ecosystems.
