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8/3/2019 Ecosystems Lec 7-8
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Ecosystems and Ecological Communities
& Succession
ENV 107: Environmental Science
Ecology
Ecology is the study of how organisms interact with each other and with their non-
living environment (including such factors as sunlight, temperature, moisture, and vital
nutrients).
What is an ecosystem?
An ecosystem encompasses all the parts of a living environment (including the plants
and animals) AND the non-living components, such as water, air and the sun's energy.
Or
Ecosystem is a community of different species interacting with one another and withtheir nonliving environment of matter and energy.
An ecosystem may be small, such as a particular stream or field or a patch of woods,
desert.
or
The units may be large, generalized types of terrestrial (land) ecosystem such as a
particular type of grassland, forest.
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An ecosystem has structure: non-living and living parts. Non-living parts include rocks, water and air. The living part is the
ecological community, which is a set of interacting species.
An ecosystem has processes. 2 basic kinds of processes must occur in the ecosystem: a cycling of chemical elements and a flow of
energy.
For example, in the presence of sunlight, green plants, algae and photosynthetic bacteria produce sugar from carbon dioxide and
water, from sugar and inorganic compounds they make many other organic compounds, including proteins and woody tissue.
The whole earths surface can be described by a series of interconnected ecosystem. All of the earths ecosystems together make up
what we call the biosphere.
Example:
Some examples of small ecosystems are tidal pools, a home garden. Larger ecosystems might encompass lakes, agricultural fields, or
stands of forests. Landscape-scale ecosystems encompass larger regions, and may include different terrestrial (land) and aquatic (water)
communities.
Ultimately, all of Earth's life and its physical environment could be considered to represent an entire ecosystem, known as the
biosphere
Species: Groups of organisms that resemble one another in appearance, behavior, chemistry and genetic
structure form a species.
Or
All the members of a specific kind of plant, animal, or microbe; a kind given by similarity of appearance or
capacity for interbreeding and producing fertile offspring.
For instance, all human beings (Homo sapiens) resemble one another in their body structure, body systems,
and they all have similar genetic structure. They are thus grouped together under the species sapiens.
Structure: An ecosystem is made up of two major parts- nonliving and living.
The abiotic or nonliving part is the physical-chemical environment, including the local atmosphere, water,
nutrients, solar energy and mineral soil.
The biotic or living part, called the ecological community (plants, animals, microorganisms, sometimes
called biota), is the set of species interacting within the ecosystem.
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Factors/ components of an Ecosystem
Abiotic Factor / All Nonliving Components
Sunlight
Temperature & precipitation,
wind
latitude (distance from the equator)
& altitude (distance above sea
level),
frequency of fire, and
nature of the soil.
Water & Moisture
Biotic Factor/ All living Organism
Human Beings
Animals
Plants
Fishes
Fungi
Bacteria
Figures: Greatly simplified diagrams of some of the biotic and abiotic components in a freshwater aquatic ecosystem and a terrestrial ecosystem.
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Major living components of Ecosystem
Producers/ autotrophs (self-feeders):Made their own food from compounds obtained from their environment:
On land, most producers are green plants.
In freshwater and marine ecosystem, algae and plants are the major producers.
In open water the dominant producers are phytoplankton.
Most producers use the photosynthesis process.
Carbon dioxide +water +solar energy Glucose + oxygen
Some use chemosynthesis. (Without sunlight)
Consumers/heterotrophs (other-feeders):
All the other organisms that do not produce their own food depend directly or indirectly
on food provided by producers.
Several classes of consumers:
Herbivores/ primary consumers (plant eaters): Some animals do not
eat other animals. They survive on plants and are known as
Herbivores.
Carnivores/ secondary consumers (meat eaters): Some animals eat
only other animals. These animals are called carnivores .
Tertiary (higher-level) consumers: feed only on other carnivores.
Omnivores: Some animals, like us, eat both plants and animals. These
animals are called omnivores.
Scavengers: feed on dead organisms that were killed by other
organisms or dies naturally. Examples: Vultures, flies, crows.Detritivores: live off detritus or parts of dead organisms and cast off
fragments and wastes of living organisms.
Detritus feeders: extract nutrients from partly decomposed organic
matter in the leaf litter, plants fragments, and animal dung. Such as
crabs, carpenter ants, termites.
Decomposers: consumers that complete the break down and recycling
of organic materials from the remains or wastes of all organisms.
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Tropic categories
AutotrophsMake their own organic
matter from inorganicnutrients and an
environmental energy
source
Producer Consumer Decomposers: organismsthat feed on dead organic
material
Primary consumers/herbivores:animals that feed exclusively
on plants
Omnivores: animals that feedon both plants and animals
Secondary consumers/carnivores: animals that feed on
primary consumers
Higher orders of consumers/carnivores: animals that feed on
other carnivores
Parasites: plants or animals thatBecome associated with other plants
or animals and feed on it over an extended
period of time
Photosynthetic green
Plants: use chlorophyllto absorb light
Photosyntheticbacteria: use purple pigment
to absorb light
Chemosyntheticbacteria: use high energy
inorganic chemicals
Decomposers:fungi and bacteria that cause
rotting
Primary detritus feeders:organism that feed directly
on detritus
Secondary and higherorders of detritus feeders:feed on primary detritus feeders
HetrotrophsMust feed on organic matter for energy
Ecological Community
It is defined in two ways:
The community consists of all the
species found in an area, whether
or not they are known to interact
and affect one another. Example:
Animals in different cages in a zoo
could be called a community.
The community is defined as a set
of interacting species found in the
same place and functioning
together to make possible the
persistence of life.
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Food chains
Individuals in a community interact is by feeding on one another. Energy, chemical
elements and some compounds are transferred from creature to creature along food chains,
a network of feeding relationship in an ecosystem.
A complex network of many interacted food chains and feeding relation ships is called a
food web.
Ecologists explained: the group organisms in a food web into trophic levels. A trophic
level consists of all those organisms in a food web that are the same number of feeding
levels away from the original source of energy.
The original source of energy in most ecosystems is the sun. In other cases, it is the
energy in some inorganic compounds.
Green plants, algae and certain bacteria produce sugars through the photosynthesis, using
the energy of the sun and carbon dioxide (CO2) from the air, so they are grouped in to the
first trophic level.
Yellowstone hot springs food chain
The simplest natural ecosystem is a hot spring such as those found in Yellowstone National Park, Wyoming. Few organisms
can live in those hot springs because the environment is so harsh. Water in parts of the springs is close to the boiling point. In
addition, some springs are very acidic and others are very alkaline.
Typically, the springs have a wide range of water temperatures, from almost boiling near the source to much cooler near the
edges, specially in the winter. In a typical alkaline hot spring, the hottest waters, between 70 C and 80C, are colored bright
yellow-green by photosynthetic blue-green bacteria. In slightly cooler waters, 50C and 60C, thick mats of bacteria and
algae accumulate.
First trophic level: Photosynthetic bacteria and algae make up the springs first trophic level, which is composed of
autotrophs. In the hot springs, as in most communities, the source of energy is sunlight.
Second trophic level: Some flies, called Ephydrid flies, live in the cooler areas of the springs. One species, Ephydra bruesi,
lays bright orange-pink eggs on stones and twigs that project above the mat. Another species, Aracoenia turbida, lays white
eggs in the mat. The fly larvae feed on the bacteria and algae. Since these flies eat only plants, they are herbivores. These
form the second trophic level.
Third trophic level: Another fly, called the Dolichpopid fly, is carnivorous and feed on the eggs and larvae of the
herbivorous flies. Dragonflies, waps, spiders, tiger beetles and one species of bird, the killdeer, also feed on the herbivorous
flies. All these form the third trophic level.
Fourth trophic level: Wastes and dead organisms of all trophic levels are fed on by decomposers, which in the hot springs
are primarily bacteria. These form the fourth trophic level.
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The entire hot springs community of organisms- photosynthetic bacteria and algae, herbivorous
flies, carnivores and decomposers- is maintained by two factors:
(1) Sunlight, which provides an input of usable energy for the organisms and (2) a constant flow
of hot water, which provides a continual new supply of chemical elements required for life and a
habitat in which the bacteria and algae can persist.
An important aspect of hot sprigs ecosystem is species dominance.
Dominant species are those that are most abundant or otherwise most important in the
community.
In the hot springs community, the species of photosynthetic bacteria or algae that is dominant,
changes with the temperature; one species dominates the hotter springs and hottest regions within
a spring and another species dominates cooler water.
Because the algae are brightly colored, this spatial patterning in dominance is readily apparent
to visitors.
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A terrestrial food chain
In a terrestrial food chain the first trophic level,
autotrophs, includes grasses, herbs and trees.
The second trophic level, herbivores includes
mice, an insect called the pine borer and other
animals (such as deer).
The third trophic level, carnivores, include foxes
and wolves, hawks and other predatory birds, spiders
and predatory insects.
People are omnivores (eaters of both plants and
animals) and feed on several trophic levels.
People would be included in the fourth trophic
level, the highest level in which they would take
part.
Decomposers, such as bacteria and fungi, feed on
wastes and dead organisms of all trophic levels.
Decomposers also belong to the fourth trophic level.
Connections: Food webs and energy flow in ecosystemsThe food chain determines how energy and nutrients move from one organism to another through an
ecosystem.
Ecologists assign each organism in an ecosystem to a feeding level, or trophic level (from the Greek word
trophos, "nourishment"), depending on whether it is a producer or a consumer and on what it eats or
decomposes.
Producers belong to the first trophic level, primary consumers to the second trophic level, secondary
consumers to the third, and so on. Detritivores and decomposers process detritus from all trophic levels.
Real ecosystems are more complex than this. Most consumers feed on more than one type of organism,
and most organisms are eaten by more than one type of consumer. Because most species participate in several
different food chains.
Each trophic level in a food chain or web contains a certain amount of biomass, the dry weight of all
organic matter contained in its organisms.
In a food chain or web, chemical energy stored in biomass is transferred from one trophic level to another.
With each transfer some usable energy is degraded and lost to the environment as low-quality heat. Thus
(1) only a small portion of what is eaten and digested is actually converted into an organism's bodily material
or biomass, and (2) the amount of usable energy available to each successive trophic level declines.
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The percentage of usable energy transferred as biomass from one trophic level to the next is
called ecological efficiency.
It ranges from 5% to 20%, (that is, a loss of 80-95%) depending on the types of species and
the ecosystem involved, but 10% is typical.
Assuming 10%, ecological efficiency (90%> loss) at each trophic transfer, if green plants in an
area manage to capture 10,000 units of energy from the sun, then only about 1,000 units of
energy will be available to support herbivores and only about 100 units to support carnivores.
The more trophic levels or steps in a food chain or web, the greater the cumulative loss of
usable energy as energy flows through the various trophic levels.
Pyramid of energy flow:
This energy loss for a simple food chain, assuming a 90%
energy loss with each transfer.
Pyramids of energy flow always have an upright pyramidal
shape because of the automatic degradation of energy quality.
Energy flow pyramids explain why the earth can support
more people if they eat at lower trophic levels by consuming
grains, vegetables, and fruits directly rather than passing such
crops through another trophic level and eating grain eaters.
The large loss in energy between successive trophic levels
also explains why food chains and webs rarely have more than
four or five trophic levels.
In most cases, too little energy is left after four or five
transfers to support organisms feeding at these high trophic
levels.
This explains why (1) there are so few top carnivores such as
eagles, hawks, tigers, and white sharks, such species usually are
the first to suffer when the ecosystems that support them are
disrupted, and (2) these species are so vulnerable to extinction.
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Ecological Succession
The balance of nature
An environmental myth that states that the natural environment, when not influenced by
human activity, will reach a constant status, unchanging over time, referred to as a balance
or equilibrium state. The major tenets of a belief in the balance of nature are as follows:
Nature undisturbed achieves a permanency of form and structure that persists
indefinitely.
If it is disturbed and the disturbing force is removed, nature returns to exactly the same
permanent state.
In this permanent state of nature, there is a great chain ofbeing with place for each
creature (a habitat and niche) and each creature in its appropriate place.
A steady state stage of succession is called a climax state that would persist indefinitely
and have maximum organic matter, maximum storage of chemical elements and maximum
biological diversity.
Ecological Succession
Recovery of disturbed ecosystems can occur naturally through a process called ecological succession. This natural recovery
can occur if the damage is not too great. Sometimes, though, the recovery takes longer than people would like. Or-
Ecological succession is the gradual process by which ecosystems change and develop over time.
To understand succession, it is necessary to clearly understand the difference between these four terms:
Habitat: A place where organisms live. e.g. a pond
Population: A group of individuals of the same species in a particular location (habitat). For example, all of the Great
Diving Beetle larvae and adults in the pond
Community : All of the populations of species in a given area. For example, all of the numerous species of micro-
organisms, plants and animals living in the pond.
Ecosystem : The Community together with chemical & physical environment of an area.
So, A-
Succession takes place because the environmental conditions in a particular place change over time
Each species is adapted to thrive and compete best against other species under a very specific set of environmental
conditions
If these conditions change, then the existing species will be replaced b y a new set of species which are better adapted to
the new conditions
As an example, the environmental conditions present on the bare patch of ground above would have been quite different 2
years later
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Bare Ground Two Years Later No plant competition for light,space, nutrients or water. Soil mobile and liable to erosionand loss. A more extreme surfacemicroclimate because the baresoil both absorbs and reflectsheat more than soil covered invegetatio n.
A drier environment becausethere is no plant cover to hold
moisture above ground and littlehumus to hold it in the soil. Lower nutrient levels in the soil.
Intense plant competition forspace and other resources. Soil bound by roots and plantcover. The plant cover provides acertain amount of groundinsulation from extremes oftemperature. There are now alsoa variety of microclimates withinthe vegetation.
Plant cover and increasinghumus levels help to retain
water.
The nutrient levels in the so il willhave increased.
Ecological succession is of two types: primary and secondary:
Primary succession: is initial establishment and development of an ecosystem. Begins with bare rock exposed by
geologic activity
Examples: bare rock exposed by a retreating glacier or severe soil erosion, newly cooled lava, an abandoned highway or
parking lot
Example: Rock -> lichen -> moss -> grass -> shrub -> trees -> oak hickory forest
Stages of Primary Succession:
Primary Succession: Establishing life on lifeless ground, Which Begins with an essentially lifeless area where there is no soil
in a terrestrial ecosystem or no bottom sediment in an aquatic ecosystem. So, the process is much slower than secondary
succession
Examples: bare rock exposed by a retreating glacier or severe soil erosion, newly cooled lava, an abandoned highway or
parking lot
Soil formation begins when hardy pioneer species attach themselves to inhospitable patches of bare rocks
Pioneer Species: These are often species which grow best where there is little competition for space and resources. Mosses
are often pioneer species.
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Primary Succession
Lichens &
Moses
Small herbs
& shrubs
Heath
Mat
Jack pine,
Black spruce
Aspen
Balsam Fir
Paper Birch
White spruce
Exposed rocks
As patches of soil build up & spread, eventually the community of lichens & mosses are replaced by a new community
Typically it consists of small perennial grasses (plants that live more than 2 years without having to reseed) and herbs (ferns in tropical area)
These are called early successional species; grow close to the ground, can establish large populations quickly under harsh conditions & have
short lives
Some of their roots penetrate in the rock to create more soil
The decay of their bodies add nutrient to the soil
After hundreds of years, the depth & fertility of the soil become capable of storing enough nutrient and moisture to support growth of mid-
successional species of herbs, grasses & low shrubs
Trees that need lots of sunlight & are adapted to local climate & soil usually replace these species
As these tree species grow and create shade, they are replaced by late successional species: mostly trees that can tolerate shade. These are also
often called climax community.
Secondary succession:
Are reestablishment of an ecosystem. Begins on soil from which previous community has been removed (by fire, agriculture,
etc.) Example: Grass --- Shrub --- Trees --- Oak ---Hickory forest
Secondary succession begins in an area where the natural community of organisms have been disturbed, removed, or
destroyed but some soil or bottom sediment remains.
Abandoned croplands, burned or cut forests, heavily polluted streams, flooded land, dammed land
As some soil/sediment is present, new vegetation can
usually begin to germinate within few weeks
Seeds can be present in soil, or they can be carried
from nearby plants by wind or deposited in the
droppings of birds and animals. In the central region of Carolina, European settlers
cleared the mature native oak & hickory forests &
planted the land with crops. Later they abandoned some
of this farmland because of erosion & loss of soil
nutrients.
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Patterns of Interaction
During succession one species replaces another. There are at least three patterns
of interaction among earlier and later species in succession:
3 patterns of interaction between earlier & later species of succession
Facilitation
Interference
Life history differences
There is also a possibility of a fourth in some cases:
Chronic Patchiness
Facilitation:
This pattern has been found to take place in tropical rain forest. Early successional species speed the reappearance of the microclimatic conditions that occur in a mature forest.
In tropical forest, temperature, relative humidity, and light intensity at the soil surface can reach conditions similar to those
of a mature rain forest after only 14 years.
Once these conditions are established, species that are adapted to deep forest shade can germinate and persist.
Sand banks and bogs also illustrate facilitation. Sandbank grasses anchor the sandy soil so that seeds of plants that fall on
the ground have a chance to germinate before they are buried too deep or blown away again.
Sedges that form floating mats on the waters of a bog create a substrate where seeds of other species can lodge, germinate,
and grow.
Example: Pine & Oak. Pine provides the shade and act as nurse trees for oak. If there is no pine, few or no oaks
will grow. Pines facilitate the entrance of oak.
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Interference:
Interference can be found in tropical rain forests.
Early successional species may in some way prevent the entrance of later successional species.
When a rain forest is cleared, used for agriculture, and then abandoned, perennial grasses grow that form dense mats.
For example: in parts of Asia, these include bamboo and Imperata, as well as thick-leaved small trees and shrubs.
Together, these form stands so dense that seeds of other, later successional species cannot reach the ground, germinate, or
obtain enough light, water, and nutrients to survive. Imperata either replaces itself or is replaced by bamboo, which then
replaces itself.
Once established, Imperata and bamboo appear able to persist for a long time.
Life History Differences:
One species may not affect the time of entrance of another; two species may appear at different
times during succession because of differences in transport, germination, growth, and longevity
of seeds.
There is actually a fourth possibility: Succession never occurs and the species that enters first
remains until the next disturbance. This fourth case is called chronic patchiness.
Each of these processes occurs in nature.
Chronic patchiness: Succession depends on the common interaction between life and its
environment. In the harsh environment (deserts), energy and chemical elements required for life
are limited and disturbances are frequent. In this place, physical or degrading elements dominate
and succession does not occur. Again in highly polluted environments, sequence of species
replacement may not occur
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Bog Succession:
A bog is a body of water with acid waters and little if any surface
outflow, so the waters have little current.
Succession in a bog is a process that begins with open water and
ends with a forest.
Bog succession can be observed easily because the pond fills in
from the edges toward the center.
The center is successionally the youngest, and the bogs original
edge is the oldest.
In the quiet waters of the open part of a bog, sedge plants form
floating mats that grow out over the waters surface.
These short-lived shrubs are the pioneers.
Their mat of thick, organic matter forms a primitive soil into
which seeds of other plant species fall and germinate.
Sediments also build up on the bottom made up of dead organic
matter from aquatic animals and plants. The bog slowly fills in
from the bottom to the top.