Ecosystems Lec 7-8

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.

Documents

Ecosystems Lec 7-8