LAST WORD ABOUT BIOMES
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Be familiar with the names,
location (latitude, altitude),
rainfall pattern (seasonal or
constant), rainfall amount (low,
moderate, high),
$ Pay attention to productivity: the most productive biomes
form the basis for agriculture patterns, population patterns and
carbon recycling. Damage to these biomes causes greater
problems than damage to unproductive biomes.
$ Why is productivity and efficient resource usage so
important? Because they sustain human populations. Pay
particular attention to: arable land, good nutrient cycling,
presence of clean fresh water.
Productivity is the key to successful food webs. Recall:
$ Gross productivity is sunlight converted to chemical energy per
unit time. Net productivity is gross productivity - respiration
energy.
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Productivity is expressed in joules/m2/year or kg/m2/year
(energy/area/time or biomass/area/time)
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Where on earth is per-unit productivity highest?
Rainforests, tropical ocean reefs, marshlands, temperate forests,
estuaries, grasslands, crops, taiga, upwelling zones, lakes/rivers,
ocean, tundra and deserts.
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Where is the greatest total production? Ocean, rainforest,
grasslands, temperate forests and crops.
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NOTICE: Most productive areas are also under the greatest
environmental pressure. This is the root of our environmental
problems!
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ALSO NOTICE: Just because a biome is productive, it doesn’t
mean it is flexible! Rainforest soil is highly productive yet
makes terrible farmland!! Human populations are growing
rapidly in rainforest biomes, and the forests are being cut down
to make farms. This is a huge problem.
What limits productivity?
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Light and nutrients (nitrogen/phosphorus) limit productivity in
water ecosystems. Light penetrates down only a few meters.
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Temperature, moisture and nutrients limit productivity on land that’s why nutrient cycling is so important. It is also why
deserts/tundra are poor producers.
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Arable land is that which is suitable for farming. You need:
rich soil, adequate water, fairly flat geography. Use of arable
land for farming results in medium productivity.
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Note that water management (e.g. creation of reservoirs and
aqueducts) captures seasonal rainfall and snowfall and stores it
for future use (limiting runof). This allows for irrigation systems
that increase the amount of arable land.
Aquatic Biome Answers
Lake Biomes
Ocean Biomes
Availability of light is the primary factor determining productivity
in all aquatic biomes. Photosynthesis occurs in photic zone (top 10
meters) and chemosynthesis is basis of food chains in benthic zones.
Other factors include adequate nutrients, availability of organisms
to cycle nutrients properly, absence of toxins and pollutants.
Land biomes have a distinctive climate and very similar
flora/fauna, regardless of where they are located in the world.
Similarly, fresh and salt water biomes are similar around the world.
Their abiotic factors (latitude, altitude, rainfall, snowfall, coastal or
inland location, temperature, rainfall pattern, temperature patterns,
weather, climate) are extremely similar.
Biotic factors (plant and animal species, richness of soil, density of
organisms) vary somewhat, but are still quite similar.
ENERGY FLOW IN FOOD WEBS
$ Producers convert sun’s energy to food energy (kcal). About
1% of solar energy is converted to food.
$ The flow of energy goes from producer ➔first order consumer
➔secondary consumer ➔tertiary consumer.
$ Consumers convert only about 10% of their food energy to
biomass. A maximum of 10% of energy is “retained” in
organisms living at each trophic level. The rest is used for
activity and metabolism.
 To figure out energy at each trophic level:
Find energy in producers.
10% kept at each trophic level - do the math up the food chain.
$ To figure out biomass at each trophic level:
Find producer biomass. Then, 2nd trophic level retains:
Producer kg x 10% x kcal/g producer*
kcal/g consumer*
Find producer energy. Then 2nd trophic level retains:
Producer energy x 10% x g/kcal consumer*
* recall plants = 4 kcal/g, animals = 5 to 6 kcal/g. Use these
values to convert plant energy content to plant biomass or animal
energy content to animal biomass.
NOTES ABOUT BIOLOGICAL CONCENTRATION OR
BIOMAGNIFICATION
This phenomenon occurs with many
pesticides and pollutants.
Producers and first order consumers are
generally unaffected, because the [toxin]
remains below harmful levels.
Animals at higher trophic levels retain only
10% of the energy they consume, but most of
the toxins. This occurs because toxins are
fat-soluble and accumulate in flesh.
Therefore, the [toxin] increases at each
trophic level. Eventually, it reaches a
harmful level.
THE INFAMOUS CASE OF
DDT, a common pesticide, which
entered oceans via agricultural
runoff. It bio-concentrates in birds
that eat animal flesh.
$ Predatory birds such as pelicans
are high in the food chain and
accumulate DDT due to high
[DDT]in prey and repeated
consumption.
$ DDT causes weakened shells, resulting in low birth rates and
ultimate decline in populations.
$ This is an environmental activist success story; scientists
lobbied for the ban of DDT, and bird populations recovered.
Oh What a Tangled Web we Weave . . .
1. Label each trophic level. How many levels
are there?
2. Label the producers, 2o consumers and top
predator.
3. State the snake’s role in this food web.
4. Calculate energy flow:
a. With 5 x 1020 Calories sunlight, how
many Calories of plants?
b. With 2 x 1010 Calories of cacti, what is the biomass?
c. How many Calories of cactus plover?
d. If the grass contains 5 x 108 Calories, what is its biomass?
e. If the bugs contain 6 kcal/g, what is the biomass of bugs?
Answers
1. 4 trophic levels. Plants and seed pods are producers, bugs and voles are consumers, scorpions & lizards &hawks & snakes are
secondary consumers (3rd level). Note that organisms can occupy multiple trophic levels depending upon diet.
2. Producers are plants. 1o consumers are cactus plover & insects. 2o consumers are lizards, scorpion and hawk. The hawk is also a
top predator, as is the roadrunner.
3. The snake’s role is a secondary consumer, carnivore and predator.
4. Calculate energy flow:
a.
Given 5 x 1020 Calories of sunlight, use the 1% rule.
5 x 1020 x 10-2 = 5 x 1018 Calories of plants
b.
2 x 1010 Calories x 1 g/4 Cal = 5 x 109 g cactus
c.
2 x 1010 Cal x 10-1 = 2 x 109 Cal. in the plovers.
d.
5 x 108 Cal. grass x 1 g/4 Cal = 1.3 x 108 g grass
e.
(5 x 108 Cal. grass) x 10-1 x (1 g/6 Cal) =
8 x 106 g of bugs