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Chapter 36 Communities and Ecosystems
1. Community
a. assemblage of all the populations of organisms living close enough together for
potential interaction
b. Defining Characteristics
i. biodiversity
ii. prevalent forms of vegetation
iii. response to disturbance
iv. trophic structure
c. Characteristics
i. Biodiversity
1. Two components
a. species richness – total # of different species
b. relative abundance of different species
i. Ex. Community1: 25A, 25B, 25C, 25D
Community 2: 97A, 1B, 1C, 1D
ii. species richness is the same
iii. relative abundance is different
ii. Prevalent vegetation (applies mostly to terrestrial)
1. Ex. temp. deciduous forests
a. deciduous trees are most prevalent
b. forests are structured (places for organisms to live)
i. trees make canopy
ii. shrubs and lower branches
iii. herbs carpet floor
iii. response to disturbances (fires, floods, etc…)
1. cedar and hemlock trees are highly stable and can resist fire
a. if they do burn, they take a long time to return
2. grasslands – adapted to fire and rely on it
iv. trophic structure
1. feeding relationships among the various species
a. ensures passage of energy and nutrients from plants to
herbivores to carnivores
2. The various kinds of interactions between species (competition, predation and symbiosis)
a. Competition may occur when a resource is shared (REMINDER: members of
same species also compete with each other)
i. interspecific competition – 2 or more species competing for same
resource
1. both populations may be inhibited
a. Why do we pick weeds out of our gardens?
b. Lynx and fox compete for snowshoe hares in Alaska and
Canada.
ii. competitive exclusion principle
1. proposed by G. F Gause – Russian ecologist
a. Took two closely related paramecium and grew each to
carrying capacity (max. population)
i. Paramecium aurelia
ii. Paramecium caudatum
b. mixed them together
2.
3.
4.
5.
c. aurelia beat out caudatum and caudatum went extinct
d. conclusion: two similar species competing for same
resource cannot coexist in the same place.
Barnacle example
a. Balanus and Chthamalus
b. both grow on rocks exposed at low tide
c. Chthamalus – can withstand longer periods out of water,
grows on top parts of rocks
d. Balanus – grows on lower parts
e. remove Balanus and what happens? Chthamalus fills in
f. Add Balanus back and they take over bottom parts again
i. Chthhamalus can’t compete with Balanus and is
pushed out of space
Ecological Niche – species role in its community (sum of all its
uses of the biotic and abiotic factors resources) – how they make
their living
a. temp range which organism lives
b. time of day they feed
c. type of food they eat
d. What are some aspects of the barnacles niche?
i. attachment site on rocks
ii. food it eats
iii. exposure to seawater and air
Niche concept + competitive exclusion principle = two species
cannot coexist if their niches are too similar
What are two possible outcomes of competition between 2
species with identical niches?
a. local extinction of one
b. evolve through natural selection before extinction to
alter niche enough to thrive – resource partitioning
i. Galapagos finches and beak size to specialize on
different food sources may be the ghost of
competition past
3. Predation leads to diverse adaptations in both predator and prey (36.3)
a. Predation
i. consumer = predator
ii. food = prey
1. not just animal-animal, plant-herbivore too
iii. parasitism – parasite lives on or in host and gets nutrients from it is a
form of predation.
iv. potent factor of adaptive evolution
1. most predators have acute senses to locate prey
2. speed, agility, claws, teeth, fangs, stingers, poison, etc…
v. Co-evolution – observed in some predator prey relationships - series of
reciprocal adaptations in two species
1. change in one species acts as a selective force (agent) on the
other
2. counteradaptation of second species then affects selection of the
first and so on…
3. Ex. Fig. 36.3A
a. passionflower plants makes poison to protect leaves
from most herbivores
b. Heliconius caterpillar adapted to be able to eat leaves
c. passionflower then adapted to make sugar deposits that
look like eggs of Heliconius since butterfly form will
avoid leaves that already have eggs on it
d. Moreover, yellow sugar deposits and other yellow spots
attract ants and wasps that prey on Heliconius eggs and
larvae
vi. Plants have all sorts of protection against predators since they can’t run
1. chemical toxins
a. strychnine – made by a tropical vine (Strychnos toxifera)
b. morphine – from the opium poppy
c. nicotine – tobacco plant
d. mescaline – peyote cactus
e. insect hormone analogs – cause abnormal development
2. spines and thorns
vii. Animal defenses
1. Mechanical defenses
a. porcupines sharp quills
2. Chemical defenses
a. these are often brightly colored as a warning – makes it
easy for predators to learn
i. poison arrow frog – Costa Rica
ii. human hunters may tip arrows with poisons
from similar frogs to bring down large mammals
3. Mimicry
a. Batesian mimicry
i. harmless species mimics a harmful one
1. Hawkmoth larva puffs up head to look
like snake, waves head back and forth
and hisses
b. Mullerian mimicry
i. two unpalatable species in same community
mimic each other
ii. if you learn on one, you don’t try the other
1. cuckoo bee and yellow jacket
4. Predation can maintain diversity in a community (36.4)
a. Robert Paine – American Ecologist - 1960’s
i. removed dominant predator (sea star of genus Pisaster) from intertidal
zone of Washington coast
1. result: main prey (mussel) outcompeted other shoreline
organisms (algae, barnacles, snails) for space on rocks
2. species dropped from 15 to 5
ii. Keystone species
1. one that exerts strong control on community structure
2. Pisaster sea star
3. Sea otters – keystone predator in North Pacific
a. reduced by fur trade 1800’s
b. feed on sea urchins
c. sea urchins feed on kelp
d. now they are thought to be eaten more by killer whales
because seals and sea lions have declined because of a
decline in fish
e. fish decline from human overfishing in North Pacific
iii. Add question from 36.4
5. Symbiotic relationships help structure communities
a. symbiotic relationships
i. interaction b/w 2 or more species that live together in direct contact.
ii. Three main types
1. parasitism
a. type of predator prey relationship
b. Usually smaller than host
c. Example
i. Wasp – Apanteles glomeratus
ii. stabs through skin of caterpillar(Pieris rapae)
and lays eggs
iii. larva will grow within, gaining nutrients and
energy from internal organs and kill caterpillar
iv. Another wasp – ichneumon – finds caterpillars
with apanteles larva and injects her larva in them
v. A third wasp (chaclid) may deposit its eggs in
the ichneumon larva!
vi. Caterpillar houses a three step food chain –
chalcid larva eating ichneumon larvae eating
Apanteles larvae eating the caterpillar!
1. chalcids will emerge
d. tapeworms
e. ticks
f. aphids
g. Natural selection favors parasites that can absorb
nutrients from host best, as well as hosts that can best
defend themselves against parasites.
i. result: stable relationship where host is not killed
ii. Example
1. 12 pairs of rabbits brought to Australia
for hunting on an estate in 1800’s
2. 1940’s hundreds of millions of
European rabbits plagued Australia (Fig.
36.5A) – destroyed Australia
3. myoxoma virus – parasite that infects
rabbits
a. deliberately introduced to
control rabbit population
b. what do you think happened?
c. spread rapidly by mosquitoes
and devastated rabbit population
d. some rabbits could survive –
natural selection
e. those strains that killed hosts
quickly died with host – natural
selection favored strains that
infect but not kill
f. host-parasite relationship was
stabilized and today they coexist
2. commensalism
a. one partner benefits while the other is unharmed
i. few cases likely exist
1. algae growing on turtle shells
2. barnacles on whales
3. birds feeding on insects flushed out of
grass by grazing cattle
3. mutualism
a. both parties benefit
i. flowering plants and insects
ii. legume plants and their nitrogen fixing bacteria
iii. bulls horn acacia tree (Central and south
America)
1. ants (pseudomyrmex) live in large
hollow thorns and eat sugar secreted by
tree and yellow structures rich in protein
(Fig. 36.5B) – no known function other
than attract ants.
2. ants attach anything that touches the
tree.
a. sting other insects and
herbivores
b. clip surrounding vegetation near
tree!
3. remove ants and tree usually dies – must
now compete for light and herbivores
damage it.
iii. Bottom Line – community structures are highly dependent on
interactions b/w different species
6. Disturbance is a prominent feature of most communities (36.6)
a. Disturbances
i. storms, fire, flood, drought, overgrazing, human activities
ii. damage biological communities, remove organisms, alter availability of
resources
iii. type, frequency, severity vary from community to community
1. ex- fire affects many terrestrial communities
2. storms affect almost all
b. Disturbances are not always negative
i. fall of dinosaurs, rise of mammals
1. can create opportunity for other species
ii. fallen tree (lightning, age, etc…)
1. leaves opening for other organisms
a. root depression fills with water and becomes a breeding
ground for frogs, salamanders and other insects
iii. severe disturbance
1. communities change drastically
a. flood, fire, glacial advance or retreat, volcanic eruption
strips away vegetation
b. Ecological Succession – open area gradually colonized
by fast growing species and slowly replaced by a
succession of others.
i. Primary succession – first community to arrive
in a lifeless area
1. ex) new volcanic island
2. often autotrophic organisms are the first
to arrive
3. Lichens and mosses
a. grow from wind blown spores
b. First photosynthetic organisms
to arrive
c. Lichen – symbiotic relationship
of fungus and algae or
cyanobacteria
4. No soil yet
a. develops as these initial
organisms die and decompose
5. Soil present
a. grasses, shrubs, trees overtake
moss and lichen
6. barren soil to forest – 100’s to 1000’s of
years
ii. Secondary succession
1. Disturbance destroys existing
community but soil intact.
2. Ex. forested area cleared, farmed,
abandoned may return to a forest
3. Earliest plants – herbaceous (nonwoody) plants from windblown or
animal carried seeds
4. Under the right condition – woody
plants (shrubs) replace herbaceous ones
and trees may replace those
c. Climax Community
i. The permanent final stage community for a
given climate and soil type
ii. Some communities may never reach a climax
due to disturbance
1. some prairies would become forest in
not for grazing and fire
d. What is the major abiotic factor that distinguishes
primary from secondary succession?
7. Ecologist Frank Gilliam discusses the role of fire in ecosystems (36.7)
a. “Today we realize that we cannot afford to view fire as the destructive scourge
we used to hear about. Like wind, rain, soil, and chemical nutrients, it is an
important abiotic factor, even a creative force, in many ecosystems.”
b. designed around fire
i. If an ecosystem typically has a rapid build up of fuel, periodic drought,
etc… it is likely designed around fire
ii. temperate deciduous forests
1. periodic rain
2. fuel is fairly quickly decomposed
3. not designed for fire
iii. Southeastern pine forests
1. needles build up (hard to break down)
2. acidic soil – reduces decomposition
3. seasonal droughts common
4. fires burn every 5-7 years
5. Large pines can make it through
6. I fuel is allowed to build up too much, they might be killed
7. so should humans prevent natural fires?
iv. Prairie Grasslands (Kansas)
1. tall dry grass is perfect fuel
a. aerated, nothing blocking wind
b. all you need is a spark (lighting)
2. burn every 2-4 years under NATURAL condition some every
year
3. Tall prairie grass depend on fire
a. there is enough rain for shrubs and trees to grow
b. need fire to stop this
8. Energy flow and chemical cycling are the two fundamental processes in ecosystems
a. ecosystem – biotic community and abiotic environment
i. two fundamental processes of an ecosystem
1. energy flow (remember, energy is motion or ability to move) –
passage of energy through the components of an ecosystem
a. light energy from sun  photoautotrophs convert light
to chemical energy (sugar)  heterotrophs obtain some
of this chemical energy, heterotrophic bacteria and fungi
in the soil get their share from dead organisms.
b. Every use (conversion) of energy results in some lost to
surroundings as heat (2nd law of thermodynamics)
c. need a constant input
2. chemical cycling
a. circular motion of chemical within the ecosystem
b. ecosystems are self-contained in terms of materials
c. elements (i.e. carbon, nitrogen, etc…)
i. cycled between biotic and abiotic
ii. plants
1. acquire elements in inorganic form from
air (CO2) and soil (N, P, S, etc…)
2. fix into organic form (sugars, etc…)
iii. animals
1. consume the organic form
iv. plants and animals die
1. microorganisms return most elements in
organic form to soil and air
2. plants and animals also return some
inorganic form to soil and air
d. energy flows in and out, chemicals cycle
9. Trophic structure is a key factor in ecosystem dynamics
a. trophic structure – pattern of feeding relationships in an ecosystem
i. determines route of energy flow and pattern of chemical cycling
b. food chain
i. sequence of food transfer from trophic level to trophic level (36.9A)
1. Producers – autotrophs (present in ALL ecosystems) –
autorophs (chemo or photo)
a. land – plants
b. aquatic –
i. phytoplankton – main producers photosynthetic protists and cyanobacteria
(photosynthetic bacteria)
ii. multicellular algae and aquatic plants also in
shallow waters
2. Consumers (heterotrophs) - all organism above producers
a. depend on producers one way or another
b. primary consumers – herbivores
i. eat plants, algae, autotrophic bacteria
1. land – insects, snails, vertebrates that
graze and eat seeds (birds) etc…
2. aquatic – zooplankton (protists and
microscopic animals such as tiny
shrimp) that eat phytoplankton
c. secondary consumers (carnivores)
i. eat primary consumers
ii. land
1. small mammals like some mice (eat
herbivorous insects), many small birds,
frogs, spiders, lions and other large
mammals that eat grazers.
iii. aquatic
1. small fish that eat bottom dwelling
(benthic) invertebrates and zooplankton
d. Tertiary consumers
i. ex) snakes that eat mice
e. quarternary consumers
i. hawks and killer whales etc…
3. Decomposers (saprobe or saprotroph) – not shown in 36.9A
a. decomposition – break down of organic materials to
inorganic ones (by definition, all organisms are
decomposers to some extent)
b. Consume detritus - the non-living organic material
i. dead plants and animals
ii. parts of organisms (fallen leaves)
iii. waste
c. scavengers – animals that feed on dead animals
i. vultures, catfish, crayfish
ii. earthworms, many rodents, insects (eat fallen
leaves)
d. Detritivores – animals that consume already
decomposing organic material
i. dung beetles
ii. earthworms
e. saprotrophic bacteria and fungi
i. the main decomposers (recyclers)
1. take care of everything not taken care of
by other organisms
2. secrete enzymes to digest organic
materials and absorb breakdown
products
3. convert most of ecosystems organic
material back to inorganic for the
producers
4. also eaten by consumers
5. found in soil and mud at bottoms of
lakes and oceans
6. needed by ALL ecosystems to recycle
chemicals
7. link all the trophic levels
8. without these organisms, dead remains
and waste would persist for quite a long
time without ever being recycled and
chemicals would stay locked up in
them!
c. Food chains are an oversimplificaton
i. natural ecosystem rarely if ever have a linear food system
d. If I am eating a slice of pizza, what trophic level(s) am I feeding?
i. flour and tomato sauce – primary consumer
ii. cheese – secondary consumer
1. an organism can be at different trophic levels, your not stuck
10. Food chains interconnect to form food webs (36.10)
a. food web – a network of interconnected food chains (Fig. 36.10)
i. can have many producers
ii. consumers may eat more than one type of produce
iii. several species may feed on same primary consumer
iv. some secondary consumers are also primary consumers
v. Even this figure is way over simplified
vi. Even consumers of the highest level eventually become food for?
1. decomposers
11. Food chain length is limited by energy supply
a. Earth receives 1019 kcal of energy per day from sun (100 million atomic bombs)
i. most absorbed, scattered or reflected by Earth’s atmosphere and surface
ii. Of the visible light that reaches plants, algae and cyanobacteria, 1% is
converted to chemical energy by photosynthesis
1. 170 billion tons of organic material/year produced
2. biomass – the mass (amount) of living matter in biosphere
3. primary production – amount of solar energy converted to
chemical energy by photoautotrophs in a given time period
a. 170 billion tons of biomass/year
b. ecosystems vary
i. open ocean – low production, contributes most
because of large size
ii. tropical rain forests – cover only 3% of Earth,
but they contribute as much as ocean – high
production
iii. Pyramid of production (Fig. 36.11)
1. each tier represents a trophic level
2. width of bar indicates amount of energy passed on from level
below it in a year
3. shows the cumulative loss of energy in food chain (web)
a. producers convert 1% of sunlight
b. 10% of that energy makes it to the primary consumers
and so on….
c. efficiencies of energy transfer range from 5-20%
depending on organisms
i. 80 – 95% of energy never makes it to next level
4. producers to primary consumers
a. herbivores only eat a fraction of plant material
b. can’t digest everything they eat
c. that which is absorbed by herbivore
i. 2/3 as fuel for cellular resp. (making ATP)
ii. only 1/3 left over to be consumed by the next
level
iii. This same process continues up the food chain
iv. Result: Amount of energy available to top level consumers is small
1. ~1/1000th the energy that producers fix makes it to a tertiary
consumer
v. Top-level consumers
1. So why do top-level consumers like lions and hawks need to
much territory?
a. takes a lot of vegetation to support all the layers before
these predators
2. Top-level consumers tend to be large
a. so that small amount of energy available to them is
stored in a limited number of individuals
3. Results: Populations are typically small and habitats are large
a. makes predators highly susceptible to extinction
vi. Most food chains are limited to three to five levels because you run out
of energy
vii. Why is a pound of bacon so much more expensive than a pound of corn?
1. Took at least 10 pounds (10 times as much) corn feed to produce
the pound of bacon.
12. Production pyramids explain why meat is a luxury for humans
a. omnivores – eat both plant and animals (humans)
i. humans are all of the trophic levels except decomposers
b. How does the amount of corn needed to be grown to support a vegetarian
compare to that needed to support a meat eater?
i. When people eat corn, we have 10X more energy available to us
compared to when we eat meat.
ii. Takes 10X more energy to feed us when we eat meat
1. likely closer to 100X since cows are endothermic (warmblooded) and use a lot of energy keeping themselves warm
iii. eat meat
1. need more land
2. more water
3. more fertilizers and pesticides
4. 1 pound of beef takes 2500 gallons of water, 16 pounds of grain,
35 pounds of topsoil and energy equivalent to a gallon of
gasoline.
13. Chemicals are recycled between organic matter and abiotic reservoirs
a. Life depends on recycling of chemical nutrients
i. there are no sources outside of Earth to get chemicals
b. Biogeochemical cycles
i. water cycle
ii. carbon cycle
iii. nitrogen cycle
iv. phosphorous cycle
c. in each cycle, the elements bounce between abiotic and biotic components
14. Water cycle
a. global cycle
b. driven by heat from the sun
c. move b/w land, oceans, and atmosphere depend on:
i. precipitation
ii. evaporation
iii. transpiration from plants – evap of water from the aerial parts of plants
through stomata - move water from ground to atmosphere
d. Figure 36.14
i. annual water movement in parentheses (x 1018)
ii. width of blue arrows indicate amounts
iii. over ocean
1. evap. exceeds precip. – good thing!
2. wind carries excess water vapor over land as clouds
iv. on land
1. precip. exceeds evap. and transpiration
2. excess water forms lakes, rivers, ground water
a. all flow back to the sea completing cycle
v. global
1. water is blown around in atmosphere
2. water molecule evaps from pacific ocean and ends up in rain the
hits long island and then I drink it. Now it is in one of my cells
and so on…
vi. human impace
1. transpiration
a. major source of atmospheric water from dense
vegetation of rainforests
b. destroy rainforests and you reduce water in atmosphere
c. alter local and likely global weather patterns
2. pumping groundwater up for irrigation
a. increases rate of evaporation over land
b. if not balanced by increased rainfall over land
c. groundwater will be depleted
i. Large areas already face this problem
1. Midwestern US
2. SW American desert
3. parts of California
4. areas bordering gulf of Mexico
15. Carbon Cycle
a. depends on photosynthesis and respiration
b. atmospheric reservoir (like water) as CO2 (0.03%)
c. Figure 36.15
i. CO2 is converted to organic compounds by photoautotrophs (plants,
algae, cyanobacteria)
ii. Some organic material eaten by primary consumers (their carbon source)
iii. higher level consumers eat lower level for carbon
iv. decomposers pick up the rest from leaf litter, dead organisms, animal
waste etc...
v. cellular resp by all these organisms converts organic back to CO2
vi. return by respiration balances removal by photosynthesis
vii. human impact
1. increased burning of wood, fossil fuels raises CO2 levels
2. important in global warming
16. Nitrogen Cycle
a. atmospheric nitrogen (almost 80%)
b. Nitrogens in N2 are very tightly bound (triple bond)
c. most nitrogen cycles in light purple of 36.16
d. Plants cannot break
i. need nitrogen as:
1. nitrate (NO3-)
2. ammonium (NH4+)
e. Nitrogen fixing bacteria (NFB)
i. make ammonium from atmospheric N2
ii. NFB in roots of many legumes (peas, beans, etc…) and in soil
1. convert N2 to NH3, becomes NH4+ under acidic conditions
f. Nitrifying bacteria
i. convert NH4+ to NO3-, the main source of nitrogen for plants
g. plants
i. use NO3- to make amino acids (proteins)
ii. now available to consumers
h. decomposers (bacteria and fungi)
i. decompose nitrogen containing detritius back to NH4+
i.
denitrifying bacteria
i. complete cycle
ii. convert NO3- back to N2
j. Some NO3- and NH4+ are made in atmosphere by reaction of N2 with NH3
i. reach ground in dust or rain
k. Aquatic ecosystems
i. cyanobacteria fix nitrogen
l. human impact
i. Sewage treatment plants pour inorganic nitrogen into rivers, streams,
etc…
ii. farmers apply inorganic nitrogen fertilizers to crops
1. ammonium compounds and nitrates
iii. Lawns and golf courses get their share of fertilizer
1. some taken up by plants
2. some converted to N2 by denitrifying bacteria
3. excess enter streams lakes and groundwater
iv. So what?
1. Algae population usually limited by nitrogen availability
a. algae now blooms in rivers and lakes
2. groundwater pollution
a. nitrates in drinking water converted to nitrites in human
digestive system
i. nitrites can be toxic
3. Solution – check module 32.10
a. organic farming
i. relies on principles of ecology rather than
pesticides
ii. use beneficial insects to combat harmful ones
iii. use manure or compost to fertilize
iv. usually picked when ripe and sold locally (no
preservatives)
v. the organic label is no guarantee
17. The phosphorus cycle
a. depends on weathering of rock
b. different than C, N, Water whose main reservoir is in atmosphere
i. same for K and Ca
c. phosphates
i. compounds containing PO43d. weathering of rock adds phosphates to soil
e. plants, algae, etc… (autotrophs)
i. absorb dissolved phosphate ions
ii. incorporate them into organic material (DNA, ATP, etc…)
f. comsumers
i. eats plants
g. phosphate returns to soil
i. excretion (removal of wastes) by animals
1. extra phosphate removed in urine
ii. decomposers release from detritus
h. Some phosphates drain into the sea
i. may become parts of new rock
i.
ii. stuck until uplifted by geological processes and weathered
weathering is slow
i. phosphate available to plants and algae is often quite low
1. can limit plant growth
2. can limit algae growth in lakes
a. helps keep water clean
ii. human impact
1. excess phosphate can be a huge problem
a. phosphate are a major component of sewage like
nitrogen compounds
b. found in fertilizer, pesticides, detergents in the past
c. leads to heavy algal blooms in lakes
18. Ecosystem alteration can affect chemical cycling
a. Hubbard Brook Experimental Forest – began in 1963
i. White Mountains of New Hampshire (temperate deciduous)
ii. several valleys
1. each drained by a small creek
2. all creeks drain into Hubbard Brook (they are tributaries)
iii. measured the amount of water and other key nutrients (NO3-, Ca2+,
etc…) in six valleys
iv. built a dam at the bottom of each of the six streams before they met with
the main river to monitor water and nutrients.
1. Initially
a. 60% of water from precipitation went through dams
b. 40% went to transpiration and evaporation
c. flow on nutrients into and out of stream was balanced
i. small compared to recycling in the forest
2. 1966 – one of the valleys was logged and sprayed with herbicide
for 3 years to prevent regrowth of plants. (Fig. 36.18B)
a. all original plant material left to decompose
b. Result
i. water runoff?
1. increased 30-40%
2. no plants to absorb and transpire water
ii. nutrient loss from forest?
1. huge (Fig 36.18C)
2. nitrate loss was 60X greater than control
valley
3. no plants to take up and hold nitrate
4. nitrate levels in stream unsafe for
drinking
3. Other findings
a. acid rain – dissolve Calcium from forest soil
b. streams carried it away
c. Hubbard Brook forests hardly grow due to lack of Ca2+
19. David Schindler – How do the nutrients from deforested lands and agricultural areas
affect aquatic ecosystems?
a. eutrophication – algal and cyanobacteria blooms (photosynthetic organisms) as a
result of added nutrients in ponds and lakes
i. reduces oxygen levels at night
1. all the algae and bacteria are doing cellular respiration
ii. what happens to the photoautotrophs as they die?
1. sink to bottom of lake and accumulate
2. decomposers (bacteria) work on them using much of the deep
water oxygen for cellular respiration.
iii. result: lose species diversity (little oxygen)
b. experiments Schindler performed in Northern Ontario led to the banning of
phosphates in detergent (not an easy task [lobbyists])
i. companies that made phosphate detergent said it was carbon causing the
problem (eutrophication)
ii. divided a lake into two basins
1. added carbon and nitrogen to one basin
2. P + C + N in the other
3. Result
a. tremendous algal bloom in P,C,N
b. no change in C,N
c. published in science – 1974
c. Bottom line
i. acid precipitation (from acid rain)
ii. global warming
iii. changes in land use (bulldozing land for grazing, etc…)
iv. livestock egestion and excretion
v. agriculture (fertilizer, pesticides)
d. How does excessive addition of mineral nutrients to a lake eventually result in
the loss of most fish species?