Ecosystem_B.

Pharm_2nd Sem

ECOSYSTEM
Concept of an Ecosystem:
An ecosystem is a geographic area where plants, animals, and other organisms, as well as
weather and landscape, work together to form a bubble of life. Ecosystems contain biotic or
living, parts, as well as abiotic factors, or nonliving parts. Biotic factors include plants,
animals, and other organisms.
Living organisms cannot live isolated from their non-living environment because the latter
provides materials and energy for the survival of the former i.e. there is interaction between a
biotic community and its environment to produce a stable system; a natural self-sufficient
unit which is known as an ecosystem. Ecosystems are the parts of nature where living
organisms interact with themselves and their physical environment.
The term ‘ecosystem’ was coined by A.G. Tansley, an English botanist, in 1935.
An ecosystem is the structural and functional unit of ecology (nature) encompassing
complex interaction between its biotic (living) and abiotic (non-living) components.
For example- a pond is a good example of ecosystem. A pond, lake, desert, grassland,
meadows, forest etc. are common examples of ecosystems.
Levels of an Ecosystem:
1. Individual: The individual level of an ecosystem refers to a single organism of a
particular species. For example, a single oak tree in a forest.
2. Population: Population refers to a group of individuals of the same species living in a
specific area and interacting with each other. For example, a population of deer in a
forest.
3. Community: A community consists of all the populations of different species that
interact within an ecosystem. For example, a community in a forest might include oak
trees, deer, squirrels, and various bird species.
4. Ecosystem: An ecosystem includes all living organisms (biotic factors) in a particular
area and the non-living components (abiotic fwatwactors) with which they interact.
For example, a forest ecosystem includes the trees, animals, soil, water, and climate of
the forest.
5. Biome: A biome is a large-scale ecosystem characterized by its dominant plant types
and climate. For example, a tropical rainforest biome is characterized by high rainfall
and a diverse array of plant and animal species.

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6. Biosphere: The biosphere is the global sum of all ecosystems on Earth, including all
living organisms and their interactions with the physical environment. It encompasses
all of the Earth's ecosystems, from the deepest ocean trenches to the highest
mountains.

Figure 1: Levels of an ecosystem

Natural and Artificial ecosystem:

Natural ecosystems are those that occur and develop naturally in the environment without
human intervention. They are self-sustaining and consist of a complex network of living
organisms (biotic factors) and their physical environment (abiotic factors). Examples include
forests, grasslands, wetlands, and coral reefs.

Artificial ecosystems, on the other hand, are created or modified by humans for specific
purposes. These ecosystems may mimic natural ecosystems but are typically designed to
serve human needs or interests. Examples include agricultural systems, urban parks, gardens,
and aquaculture ponds.
Structure and Function of an Ecosystem:
Each ecosystem has two main components:
(1) Abiotic
(2) Biotic

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Figure 2: Structure of ecosystem

(1) Abiotic components (Nonliving): The abiotic component can be grouped into following
categories:-
(a) Climatic Factors: Which include rain, temperature, light, wind, humidity
(b) Edaphic Factors: Which include soil, pH, topography minerals etc.
Climatic factors and edaphic factors play crucial roles in maintaining ecosystem and species
richness:

Climatic Factors:
1. Light: Solar radiation is a fundamental driver of ecosystems, providing energy for
photosynthesis, which is the basis of most food chains. In equatorial regions, direct
sunlight is abundant, leading to high rates of photosynthesis and supporting diverse
plant life. In contrast, at the poles, sunlight arrives at a lower angle, reducing its
intensity and availability, limiting plant growth and species diversity.
2. Water: Water is essential for life, serving as a medium for nutrient transport in plants
and maintaining cell turgidity. Rainfall is particularly important in maintaining
species richness, especially in equatorial and plain regions where high rainfall
supports lush forests and diverse ecosystems. Adequate rainfall ensures the
availability of water for plants and animals, promoting ecosystem health and
diversity.

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3. Temperature: Temperature influences the metabolic rates of organisms, affecting their

growth, reproduction, and overall survival. The high temperatures near the equator
support high rates of biodiversity, as warm environments often promote greater
biological activity and species diversity. In contrast, the colder temperatures near the
poles limit biological activity, leading to lower species richness.
4. Wind: Wind plays a crucial role in shaping ecosystems and influencing species
richness in several ways. Wind can disperse seeds, pollen, and spores, allowing plants
to colonize new areas and maintain genetic diversity. Wind can also affect plant
growth patterns, such as the development of trees in windy areas, leading to unique
habitats that support specific species. Additionally, wind can influence nutrient
cycling and the distribution of resources, further impacting species richness in an
ecosystem.
Edaphic Factors:
1. Soil: Soil provides physical support, nutrients, and water to plants. Soil composition
affects plant growth, which, in turn, impacts the entire ecosystem. Nutrient-rich soils
support diverse plant communities and, consequently, diverse animal populations.
2. pH: Soil pH influences nutrient availability to plants and affects the microbial
community. Different species thrive in soils with specific pH ranges, contributing to
overall species richness.
3. Topography: The physical features of the land, such as slope and elevation, influence
soil formation, drainage, and microclimates. Variation in topography creates diverse
habitats, supporting a wide range of species.
4. Minerals: Soil minerals contribute to plant nutrition and growth. Different minerals
support different plant species, leading to diverse plant communities and,
consequently, diverse animal communities.
(2) Biotic components: The living organisms including plants, animals and micro-organisms
(Bacteria and Fungi) that are present in an ecosystem form the biotic components.
(A) Producers:
Green plants possess chlorophyll, a pigment that enables them to capture solar energy and
convert it into chemical energy in the form of carbohydrates, using water and carbon dioxide.
This process is called photosynthesis. Since green plants produce their own food, they are
classified as autotrophs (auto = self, trophos = feeder). The chemical energy produced during
photosynthesis is utilized partly by the plants for their growth and maintenance, with the
remainder stored in plant tissues for future use. This stored energy is crucial for the plant's

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survival, providing resources for growth, reproduction, and responses to environmental

stresses.
(B) Consumers:
Animals are unable to synthesize their own food due to the absence of chlorophyll. As a
result, they rely on consuming other organisms, such as plants or other animals, for their
energy and nutrient requirements. This dependence on external sources of food classifies
animals as heterotrophs (heteros = other, trophos = feeder).
Heterotrophs obtain energy by ingesting and digesting organic matter produced by
autotrophs. This process involves breaking down complex organic molecules into simpler
forms that can be used by the animal for energy, growth, and maintenance. Heterotrophs play
a crucial role in ecosystems as consumers, feeding on producers or other consumers, and
transferring energy and nutrients through the food chain.
(a) Primary Consumers or Herbivores: These animals feed directly on plants or producers.
Examples include rabbits, deer, goats, and cattle.
(b) Secondary Consumers or Primary Carnivores: These animals feed on herbivores.
Examples include cats, foxes, and snakes.
(c) Tertiary Consumers: These are large carnivores that feed on secondary consumers. An
example is wolves.
(d) Quaternary Consumers or Omnivores: These are the top predators in the food chain
that feed on tertiary consumers and are not preyed upon by other animals. Examples include
lions and tigers.
(e) Decomposers or Reducers: Bacteria and fungi are decomposers that break down dead
organic matter from plants and animals. They release simple inorganic and organic
substances as by-products of their metabolism, which are then reused by producers.
Decomposers are also known as saprotrophs, as they feed on decaying matter.
Examples of decomposers include:
 Bacteria: Bacteria play a crucial role in breaking down organic matter into simpler
substances. They are found in soil, water, and the digestive tracts of animals, where
they decompose organic materials.
 Fungi: Fungi, such as mushrooms and mould, are important decomposers in
ecosystems. They break down organic matter by secreting enzymes that digest
complex molecules into simpler forms.

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 Earthworms: Earthworms are soil-dwelling organisms that feed on dead plant material
and help break it down into organic matter through their digestive processes.
 Insects: Insects like beetles, ants, and flies play a role in decomposition by feeding on
decaying matter and breaking it down into smaller pieces.
 Protozoa: Protozoa are single-celled organisms found in soil and water that feed on
organic matter, helping in the decomposition process.
 Some species of nematodes: Nematodes are microscopic worms found in soil and
water that feed on bacteria, fungi, and other organic matter, aiding in decomposition.

Figure 3: Relationship within an ecosystem

Functions of ecosystem
Ecosystems are complex dynamic system. They perform certain functions. These are:
Functions of Ecosystem:
(i)Productivity,
(ii) Decomposition,
(iii) Physical (energy flow),
(iv) Biological (food chains, food web, ecological succession),and
(v) Biogeochemical (nutrient cycling) processes
(I) PRODUCTIVITY

Solar energy is crucial for ecosystem function and sustainability, providing the energy needed
for primary production. Primary production is the amount of biomass or organic matter
produced per unit area over time 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. It is

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expressed in terms of g –2 yr –1 or (kcal m–2 )yr –1 to compare the productivity of different

ecosystems. It can be divided into gross primary productivity (GPP) and net primary
productivity (NPP). Gross primary productivity of an ecosystem is the rate of production of
organic matter during photosynthesis. A considerable amount of GPP is utilized by plants in
respiration. Gross primary productivity minus respiration losses (R), is the net primary
productivity (NPP). GPP – R = NPP Net primary productivity is the available biomass for
consumption to heterotrophs (herbivores and decomposers). Secondary productivity is
defined as the rate of formation of new organic matter by consumers. Primary productivity
depends on the plant species inhabiting a particular area. It also depends on a variety of
environmental factors, availability of nutrients, and photosynthetic capacity of plants.
Therefore, it varies in different types of ecosystems. The annual net primary productivity of
the whole biosphere is approximately 170 billion tons (dry weight) of organic matter. Of this,
despite occupying about 70 percent of the surface, the productivity of the oceans are only 55
billion tons. The rest of course, is on land.

(II) DECOMPOSITION

Decomposers, like earthworms, are often called the farmer's 'friend' because they help break
down complex organic matter, such as dead plant material, into simpler inorganic substances
like carbon dioxide, water, and nutrients through a process known as decomposition. This
breakdown of organic matter is essential for soil health and nutrient recycling. Dead plant
remains, including leaves, bark, flowers, and animal remains like fecal matter, serve as the
raw material for decomposition. The decomposition process involves several important steps,
including fragmentation, leaching, catabolism, humification, and mineralization.

 Fragmentation, carried out by detritivores such as earthworms, involves breaking down

detritus into smaller particles, facilitating the decomposition process.
 Leaching: Water-soluble inorganic nutrients in detritus move downward into the soil
layers and become precipitated as insoluble salts, making them unavailable for plants.
 Catabolism: Bacterial and fungal enzymes break down detritus into simpler inorganic
substances. This process is called catabolism, which is essential for the decomposition of
organic matter.
 Humification: During decomposition, organic matter transforms into a dark, amorphous
substance known as humus. Humus is highly resistant to microbial breakdown and

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decomposes very slowly. It is colloidal in nature and acts as a nutrient reservoir in the
soil.
 Mineralisation: Some microbes further degrade humus, releasing inorganic nutrients in a
process known as mineralisation. These nutrients become available for uptake by plants
and other organisms, completing the nutrient cycle.
Decomposition primarily relies on the presence of oxygen. The rate of decomposition is
influenced by both the chemical composition of the detritus and various climatic factors.
In a given climate, decomposition tends to be slower if the detritus contains a lot of lignin
and chitin, but faster if it is rich in nitrogen and easily soluble substances like sugars.
Temperature and soil moisture are critical climatic factors that affect decomposition by
influencing the activity of soil microbes. Decomposition is favored in warm and moist
environments, while low temperatures and lack of oxygen slow down the process, leading
to the accumulation of organic matter.
(III) ENERGY FLOW
All living organisms require chemical energy from food as their main energy source,
which is transferred through different trophic levels in the food chain. This energy flow is
governed by two laws of thermodynamics. The first law states that energy cannot be
created or destroyed, only transformed from one form to another. The second law states
that as energy is transferred, some of it is lost as heat.
Energy flow in ecosystems is crucial for supporting the survival of numerous organisms.
Solar energy is the primary source of energy for almost all organisms on Earth. However,
less than 50% of the sun's radiation reaches the Earth's surface as effective radiation,
which is usable by plants for photosynthesis. This effective radiation is known as
Photosynthetically Active Radiation (PAR).
Only about 2-10% of the PAR is actually used by plants for photosynthesis. Despite this
small percentage, plants play a vital role as producers in ecosystems, supporting all other
organisms directly or indirectly. Therefore, the relatively small amount of PAR that plants
utilize is essential for sustaining life on Earth.
 Energy flow occurs through food chains and food webs.
 Plants, as producers, absorb sunlight and convert it into chemical energy through
photosynthesis.
 Primary consumers (herbivores) consume plants, converting chemical energy into
kinetic energy.

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 Energy degradation occurs through conversion into heat at each trophic level.
 Secondary consumers (carnivores of the first order) consume herbivores, further
degrading energy.
 Tertiary consumers consume carnivores, leading to additional energy degradation.
 Energy flow is unidirectional.
 Organisms occupy specific trophic levels based on their source of nutrition: producers
(first trophic level), herbivores (second trophic level), and carnivores (third trophic
level).

Figure 4: Food chain and its trophic level

 Energy decreases at successive trophic levels.

 Dead organisms are converted to detritus, serving as an energy source for
decomposers.
 Each trophic level depends on lower trophic levels for energy.
 Each trophic level has a standing crop, the mass of living material at a given time,
measured as biomass or number per unit area.
 Biomass is expressed in terms of fresh or dry weight.
 In a food chain, energy flow follows the 10 percent law, where only 10 percent of
energy is transferred to the next trophic level, with the rest lost to the atmosphere.

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Figure 5: Energy flow in an ecosystem

The 10 percent law, also known as the 10 percent rule, is a principle that describes the energy
transfer between trophic levels in a food chain. According to this law, only about 10 percent
of the energy available at one trophic level is transferred to the next trophic level. The rest of
the energy is lost as heat during metabolism, used for the organism's life processes (such as
growth, movement, and reproduction), or passed out of the ecosystem through waste
materials.

(III) BIOLOGICAL
Food Chain

The transfer of food energy from the producers, through a series of organisms (herbivores
to carnivores to decomposers) with repeated eating and being eaten, is known as food
chain. In nature, basically two types of food chains are recognized – grazing food chain
and detritus food chain.
Food chains and energy flow are the functional properties of ecosystems which make
them dynamic. The biotic and abiotic components of an ecosystem are linked through
them.
There are two types of food chains:
 Grazing food chains: these start from the green plants that make food for herbivores and
herbivores in turn for the carnivores. Ecosystems with such type of food chain are directly
dependent on an influx of solar radiation.

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This type of chain thus depends on autotrophic energy capture and the movement of this
captured energy to herbivores. Most of the ecosystems in nature follow this type of food
chain.
A simple grazing food chain (GFC) is depicted below:
The phytoplanktons →zooplanktons →Fish sequence
or
the grasses →rabbit →Fox sequences are the examples, of grazing food
chain.
Detritus food chains: start from the dead organic matter to the detrivore organisms
which in turn make food for protozoan to carnivores etc.
The detritus food chain (DFC) begins with dead organic matter. It is made up of
decomposers which are heterotrophic organisms, mainly fungi and bacteria. They meet
their energy and nutrient requirements by degrading dead organic matter or detritus.
These are also known as saprotrophs (sapro: to decompose). Decomposers secrete
digestive enzymes that breakdown dead and waste materials into simple, inorganic
materials, which are subsequently absorbed by them.
In an aquatic ecosystem, GFC is the major conduit for energy flow. As against this, in a
terrestrial ecosystem, a much larger fraction of energy flows through the detritus food
chain than through the GFC. Detritus food chain may be connected with the grazing food
chain at some levels: some of the organisms of DFC are prey to the GFC animals, and in
a natural ecosystem, some animals like cockroaches, crows, etc., are omnivores.
Food web
Simple food chains are very rare in nature because each organism may obtain food from more
than one trophic level. Thus, in an ecosystem, the various food chains are interconnected to
each other to form a network called a food web. A food web illustrates all possible transfers
of energy and nutrients among the organisms in an ecosystem, whereas a food chain traces
only one pathway of food. Food webs are very important in maintaining the stability of an
ecosystem.

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Figure 6: Difference between food chain and food web.

(III) ECOLOGICAL SUCCESSION

 Communities constantly change in response to environmental conditions.
 Changes in composition and structure parallel changes in the physical environment.
 Succession leads to a climax community in near equilibrium with the environment.
 Ecological succession is the gradual, predictable change in species composition.
 Succession starts where no living organisms exist, leading to sere(s) and seral stages.
 Diversity and biomass increase in successive seral stages.
 Present-day communities result from succession over millions of years.
 Primary succession occurs in entirely new habitats; secondary succession occurs in areas
with destroyed biotic communities.
 Hydrarch and xerarch successions progress from wet to mesic and dry to mesic
conditions, respectively.
 Pioneer species, like lichens, begin primary succession on rocks.
 Primary Succession: Occurs on a completely new habitat devoid of any previous life,
such as newly formed rock surfaces or sand dunes. The process is slow as it involves the
formation of soil. Example: colonization of lava flows by lichens and mosses.
 Secondary Succession: Begins in areas where existing communities have been disturbed
or destroyed, but soil remains intact, such as abandoned farmlands or areas affected by
forest fires. The process is faster than primary succession. Example: regeneration of
vegetation after a forest fire.

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Figure 7: Primary and Secondary succession

(IV) BIOGIOCHEMICAL PROCESSES

NUTRIENT CYCLING
Biogeochemical cycles are the pathways through which elements like oxygen, carbon,
nitrogen, phosphorus, and sulfur move between organisms and the environment. These cycles
involve processes such as respiration, excretion, and decomposition, which return elements to
the soil, air, and water. As elements move through these cycles, they form compounds with
other elements through metabolic processes and natural reactions, contributing to the cyclic
exchange of materials between living organisms and their non-living environment.
Nutrient cycles are of two types: (a) gaseous and (b) sedimentary. The reservoir for
gaseous type of nutrient cycle (e.g., nitrogen, carbon cycle) exists in the atmosphere and for
the sedimentary cycle (e.g., sulphur and phosphorus cycle), the reservoir is located in Earth’s
crust.
Environmental factors, e.g., soil, moisture, pH, temperature, etc., regulate the rate of release
of nutrients into the atmosphere. The function of the reservoir is to meet with the deficit
which occurs due to imbalance in the rate of influx and efflux.

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(1) Carbon Cycle

Figure 8: Carbon Cycle

(2) Nitrogen cycle

Figure 9: Nitrogen fixation

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Figure 10: Nitrogen cycle

(3) Water Cycle

Figure 11: Water cycle

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(4) Phosphorus Cycle

Figure 12: Phosphorus cycle

TYPES OF ECOSYSTEMS
An ecosystem consists of all the living and non-living things in a specific natural setting.
Plants, animals, insects, microorganisms, rocks, soil, water and sunlight are major
components of many ecosystems. All types of ecosystems fall into one of two categories:
terrestrial or aquatic. Terrestrial ecosystems are land-based, while aquatic are water-
based.The word “biome” may also be used to describe terrestrial ecosystems which extend
across a large geographic area, such as tundra.
(1) Terrestrial Ecosystems
The ecosystem which is found only on landforms is known as the terrestrial ecosystem. The
main factor that differentiates terrestrial ecosystems from aquatic ecosystems is the
relative shortage of water in terrestrial ecosystems and as a result the importance that water
attains in these ecosystems due to its limited availability. Another factor is the better

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availability of light in these ecosystems as the environment is a lot cleaner in land than it is in
water. The main types of terrestrial ecosystems are the forest ecosystems, the desert
ecosystems, the grassland ecosystems and the mountain ecosystems. We are going to study
all of these individually here in detail.
(a) Forest Ecosystems
These ecosystems have an abundance of flora or plants and hence in these ecosystems a large
number of organisms live in a small space. This means that these ecosystems have a high
density of living organisms. These ecosystems are classified according to their climate type
as tropical, temperate or boreal i.e; tropical evergreen forest, tropical deciduous forest,
temperate evergreen forest, temperate deciduous forest and taiga. In the tropics, rainforest
ecosystems contain more diverse flora and fauna than ecosystems in any other region on
earth. In these warm, moisture-laden environments, trees grow tall and foliage is lush and
dense, with species inhabiting the forest floor all the way up to the canopy. In temperate
zones, forest ecosystems may be deciduous, coniferous or oftentimes a mixture of both, in
which some trees shed their leaves each fall, while others remain evergreen year -round. In
the far north, just south of the Arctic, boreal forests – also known as taiga – feature abundant
coniferous trees.
(b) Grassland Ecosystems
The grasslands are the areas which comprise mainly of the grasses with a little number of
shrubs and trees. Grazing animals, insectivores and herbivores are the main types of
organisms which are found in these regions. The three major types of grasslands are the
prairies, savannas and steppes. Grassland ecosystems are typically found in tropical or
temperate regions, although they can exist in colder areas as well, as is the case with the well-
known Siberian steppe.
Grasslands share the common climactic characteristic of semi-aridity. Trees are sparse or
non-existent, but flowers may be interspersed with the grasses. Grasslands provide an ideal
environment for grazing animals. Savanna are the tropical grasslands which are dry
seasonally and have a large number of predators and grazers. Prairies are temperate
grasslands which are totally devoid of large shrubs
and trees. Prairies are of three different types, mixed grass, tall grass and short grass prairies.
(c) Desert Ecosystems
The common defining feature among desert ecosystems is low precipitation, generally less
than 25 centimeters, or 10 inches, per year. Almost 17% of all the land on this planet is
occupied by the desert ecosystems.The fauna and flora in these ecosystems is generally not

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much developed because of the high temperatures, intense sunlight and low availability of
water. The main vegetation of such regions are the shrubs, bushes and a few grasses and
trees.
The stems and leaves of these plants are also developed in order to conserve as much water as
possible. Camels, reptiles and some insects and birds are the living creatures which are found
in such regions.
Not all deserts are hot – desert ecosystems can exist from the tropics to the arctic, but
regardless of latitude, deserts are often windy. Some deserts contain sand dunes, while others
feature mostly rock.
(2) Aquatic Ecosystem
An ecosystem which exists in a body of water is known as an aquatic ecosystem. The
communities of living organisms which are dependent on each other and the aquatic
surroundings of their environment for their survival exist in the aquatic ecosystems. The
aquatic ecosystems are mainly of two types, the freshwater ecosystems and the marine
ecosystems.
(a) Marine Ecosystem
Marine ecosystems are the biggest ecosystems. They cover around 71% of earth’s
surface and also contain almost around 97% of the total water present on earth. High
amounts of minerals and salts are generally present in the water in the marine
ecosystems and to better understand the amount and composition of the different
minerals and salts in the water in different marine ecosystems. Marine ecosystems
differ from freshwater ecosystems in that they contain saltwater, which usually
supports different types of species than does freshwater. Marine ecosystems are the
most abundant types of ecosystems in the word. They encompass not only the ocean
floor and surface but also tidal zones, estuaries, salt marshes and saltwater swamps,
mangroves and coral reefs.
(b) Freshwater Ecosystem
There are three basic kinds of freshwater ecosystems and these are Lentic, Lotic, and
Wetlands. - Lentic ecosystems are stagnant or slow-moving waters like ponds or
lakes.
 Lotic ecosystems are fast-moving waters like rivers.
 Wetlands are saturated with water for extended periods.

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Pond Ecosystems – These are usually relatively small and contained. Most of the time
they include various types of plants, amphibians and insects. Sometimes they include
fish, but as these cannot move around as easily as amphibians and insects, it is less
likely, and most of the time fish are artificially introduced to these environments by
humans.
River Ecosystems – Because rivers always link to the sea, they are more likely to
contain fish alongside the usual plants, amphibians and insects. These sorts of
ecosystems can also include birds because birds often hunt in and around water
for small fish or insects. As is clear from the title, freshwater ecosystems are those
that are contained to freshwater environments. This includes, but is not limited to,
ponds, rivers and other waterways that are not the sea (which is, of course, saltwater
and cannot support freshwater creatures for very long).

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