The nature of ecosystems
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Ecosystem An array of organisms and a physical environment, all interacting through a one-way flow of energy and a cycling of nutrients Sustained by ongoing inputs of energy and nutrients (open system). The Nature of Ecosystems. Primary producers (autotrophs)

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The Nature of Ecosystems

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The nature of ecosystems

Ecosystem

An array of organisms and a physical environment, all interacting through a one-way flow of energy and a cycling of nutrients

Sustained by ongoing inputs of energy and nutrients (open system)

The Nature of Ecosystems


Overview of participants

Primary producers (autotrophs)

Obtain energy from nonliving sources (sunlight)

Build organic compounds from CO2 and water

Consumers (heterotrophs)

Get energy and carbon from organic sources

Carnivores, herbivores, parasites, omnivores

Detritivores, such as earthworms and crabs, eat small particles of organic matter (detritus)

Decomposers, such as bacteria and fungi, feed on organic wastes and remains and break them down into inorganic building blocks

Overview of Participants


Energy and nutrients

Energy flows one way

Producers capture light energy and convert it to bond energy in organic molecules (photosynthesis)

Metabolic reactions break bonds (aerobic respiration) and give off heat, which is not recycled

Nutrients are cycled

Producers take up inorganic compounds from the environment; decomposers return them

Energy and Nutrients


The nature of ecosystems

energy

input,

mainly from sunlight

A Energy from the environment flows through producers, then consumers. All energy that entered this ecosystem eventually flows out of it, mainly as heat.

PRODUCERS

plants and other

self-feeding organisms

nutrient cycling

B Producers

and consumers concentrate nutrients

in their tissues. Some nutrients released by decomposition get cycled back to producers.

CONSUMERS

animals, most fungi, many protists, bacteria

energy output, mainly heat.


The nature of ecosystems

ENERGY INPUT:

ENERGY INPUT:

ENERGY TRANSFERS:

ENERGY TRANSFERS:

Producers (photosynthesizers)

Producers (photosynthesizers)

energy lost at each conversion step from one trophic level to the next

energy lost at each conversion step from one trophic level to the next

energy in organic wastes, remains

energy losses as metabolic heat and as net export from ecosystem

energy in organic wastes, remains

energy losses as metabolic heat and as net export from ecosystem

decomposers

herbivores

carnivores

detritivores

energy inputs, outputs also occur between the two food webs

decomposers

ENERGY OUTPUT

ENERGY OUTPUT


The nature of ecosystems

Fourth-level consumers (heterotrophs):

Top carnivores, parasites, detritivores, decomposers

5th

Third-level consumers (heterotrophs):

4th

Carnivores, parasites, detritivores, decomposers

Second-level consumers (heterotrophs):

3d

Carnivores, parasites, detritivores, decomposers

First-level consumers (heterotrophs):

2nd

Herbivores, parasites, detritivores, decomposers

Primary producers (autotrophs):

1st

Photoautotrophs, chemoautotrophs


The nature of ecosystems

MARSH HAWK

CROW

HIGHER TROPHIC LEVELS Complex array of carnivores, omnivores and other consumers. Many feed at more than one trophic level continually, seasonally, or when an oppportunity presents itself

UPLAND SANDPIPER

GARTER SNAKE

FROG

WEASEL

BADGER

COYOTE

SPIDER

SECOND TROPHIC LEVEL Primary consumers (e.g., herbivores)

CLAY-COLORED SPARROW

EARTHWORMS, INSECTS (E.G., GRASSHOPPPERS, CUTWORMS)

PRAIRIE VOLE

POCKET GOPHER

GROUND SQUIRREL

FIRST TROPHIC LEVEL

Primary producers


Ecological pyramids

A biomass pyramid depicts dry weight of organisms at each trophic level in an ecosystem

Largest tier is usually producers

For some aquatic systems, pyramid is inverted

An energy pyramid depicts the energy that enters each trophic level in an ecosystem

Largest tier is always producers

Ecological Pyramids


The nature of ecosystems

top carnivores

21

detritivores + decomposers = 5,060

carnivores

383

herbivores

3,368

producers

20,810


The nature of ecosystems

Energy Input

1,700,000 kcal per square meter per year

Energy flow through living components

1,679,190 (98.8%)

B Every year 1,700,000 kcal of solar energy fall on each square meter of the Silver Springs ecosystem.

20,810 (1.2%)

producers

Energy lost as heat or to flow downstream

Energy

in wastes, remains

C 98.8 percent of this incoming energy is not captured by producers.

Energy flow to the next trophic level

4,245

D Producers harness 20,810 kcal of energy, but transfer only 3,368 kcal to herbivores. The rest is lost as heat or ends up in wastes and remains.

3,368

13,197

herbivores

2,265

720

383

carnivores

E With each subsequent transfer, only a small fraction of the energy reaches the next trophic level.

21

90

272

top carnivores

Energy output

20,810

+

1,679,190

5

16

detritivores

and

decomposers

Total annual energy flow

5,060

1,700,000 (100%)


Biogeochemical cycles

In a biogeochemical cycle, an essential element moves from nonliving environmental reservoirs, into living organisms, then back to the reservoirs

Elements essential to life (nutrients) include oxygen, hydrogen, carbon, nitrogen, phosphorus

Biogeochemical Cycles


The nature of ecosystems

biogeochemical cycle

Main nutrient reservoirs in the environment

fraction of nutrient available to ecosystem

herbivores, carnivores, parasites

primary producers

detritivores, decomposers


The nature of ecosystems

Main Reservoirs

Volume (103 cubic kiometers)

Oceans

Polar ice, glaciers

Groundwater

Lakes, rivers

Soil moisture

Atmosphere (water vapor)

1,370,00029,000

4,000

230

67

14

ATMOSPERE

precipitation onto land 111,000

wind driven water vapor

40,000

evaporation from land plants (evapotranspiration) 71,000

evaporation from ocean

425,000

precipitation into ocean 385,000

surface and groudwater flow 40,000

LAND

OCEAN


Nitrogen cycle

Gaseous nitrogen (N2) makes up about 80 percent of the lower atmosphere; most organisms can’t use gaseous nitrogen.

The nitrogen cycle starts with nitrogen fixation;

nitrogen-fixing bacteria convert N2 in the air to their own organic nitrogen compounds.

Next, other bacteria carry out ammonification, converting organic nitrogen to ammonia (NH3).

Then, still other bacteria carry out nitrification, converting ammonia to nitrite (NO2-) and on to nitrate (NO3-).

Finally, plants assimilate the nitrate into their organic compounds, closing the cycle.

Nitrogen Cycle


The nature of ecosystems

GASEOUS NITROGEN (N2) IN ATMOSPHERE

NITROGEN FIXATION

by industry for agriculture

FOOD WEBS ON LAND

uptake by autotrophs

excretion, death, decomposition

uptake by autotrophs

FERTILIZERS

NO3-

IN SOIL

NITROGEN FIXATION

bacteria convert to ammonia (NH3+) ; this dissolves to form ammonium (NH4+)

NITROGENOUS WASTES, REMAINS IN SOIL

DENTRIFICATION

by bacteria

2. NITRIFICATION

bacteria convert NO2-tonitrate (NO3-)

AMMONIFICATION

bacteria, fungi convert the residues to NH3; this dissolves to form NH4+

NH3-,NH4+

IN SOIL

1. NITRIFICATION

bacteria convert NH4+ tonitrite (NO2-)

NO2-

IN SOIL

loss by leaching

loss by leaching


Losing nitrogen from ecosystems

Denitrification

Denitrifying bacteria convert nitrate or nitrite to gaseous nitrogen (N2) or nitrogen oxide (NO2)

Human activity also removes nitrogen from the cycle via incineration (fuels and organic waste), creating a variety of air pollutants.

Ammonium, nitrite, and nitrate are also lost from land ecosystems in runoff and by leaching

Losing Nitrogen from Ecosystems


Biological magnification

Biological magnification

Some harmful substances, such as DDT, become increasingly concentrated in tissues of organisms as they move up the food chain

Biological Magnification


The nature of ecosystems

DDT Residues (ppm wet weight of whole live organism)

Ring-billed gull fledgling (Larus delawarensis

Herring gull (Larus argentatus)

Osprey (pandion haliaetus)

Green heron (Butorides virescens)

Atlantic needlefish (Strongylira marina)

Summer flounder (Paralychthys dentatus)

Sheepshead minnow (Cyprinodon variegatus )

Hard clam (Mercenaria mercenaria)

Marsh grass shoots (Spartina patens)

Flying insects (mostly flies)

Mud snail (Nassarius obsoletus)

Shrimps (compsite of several samples)

Green alga (Cladophora grcilis)

Plankton (mostlky zooplankton)

Water

75.5 18.5 13.8 3.57 2.07 1.28 0.94 0.42 0.33 0.30 0.26 0.160.083 0.040 0.00005


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