Ch.37 NOTES
COMMUNITIES AND ECOSYSTEMS
COMMUNITY STRUCTURE AND DYNAMICS
37.2 Define the following and give examples.
INTERSPECIFIC
COMPETITION
Competition
Mutualism
Predation
Herbivory
Parasitism
DEFINITION
-/- popul. of 2 different
species competes for the same limited
resource.
+/+ Both popul. benefit
+/- One species kills and eats
the other
+/- Consumption of plant
parts or algae by an animal.
EXAMPLES
Desert plants compete for water
while tropical plants compete for
light.
Plants and mycorrhizae,
flowers and pollinators.
Predator/prey: lynx and hare;
crocodile and fish
Hippo, Cattle, deer eating grass
+/- parasite/host or
pathogen/host
Heartworm/dog;
Salmonella/humans
Predation resulted in prey adapting to avoid
being seen or eaten.
 Camouflage: Color and/or texture cause
animal to blend with their environment.
Example: Gray tree frog on bark (fig. 37.5a)
 Mechanical defenses: protective quills, hard
shell of clams, oysters, turtles.
 Chemical defenses: include noxious taste or
painful sting. Predators learn to associate
bright colors with these animals. Examples:
monarch butterflies, poison-arrow dart frog.
(37.5b)
37.6 Explain why many plants have
chemicals, spines, or thorns. Define
coevolution and describe an example
Hervibory resulted in plants adapting to
avoid having to regrow eaten parts.
 Spines and thorns: roses, hawthorn trees,
cactus
 Chemical toxins: distasteful so herbivores
learn to avoid them
o strychnine: tropical vine
o morphine: opium poppy
o nicotine: tobacco plants
o mescalin: peyote cactus
o tannins: variety of plants
o sulfur: Brussels sprouts, cabbage
toxic to insects and cattle.
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Coevolution: a series of reciprocal evolutionary
adaptations in two species.
Occurs when a change in one species acts as a
new selective force on another species, and
counter adaptation of the second species in turn
affects the selection of individuals in the first
species. fig. 37.6 and lab manual cover.
37.8 Identify and compare the trophic levels
of terrestrial and aquatic food chains.
Both begin with producers (autotrophs) which
are eaten by
primary consumers (herbivores) which are
eaten by
secondary consumers (carnivores and
insectivores) which are eaten by
tertiary consumers which are eaten by
Quaternary consumers.
Detritivores and decomposers eat detritus, the
dead material produced at all levels. Examples:
earthworms rodents, insects, crows, and
vultures. Catfish and crayfish.
Decomposers secrete enzymes that digest
molecules. Examples: Fungi and bacteria
37.9 Explain how food chains interconnect to
form food webs.
fig. 37.9
 A consumer may eat more than one type of
producer and
 Several species of primary consumers may
feed on the same species of producer.
 Some animals weave into the web at more
than one trophic level.
 Examples:
o the lizard and mantid are strictly
secondary consumers, eating insects.
o The woodpecker is a primary
consumer when it eats cactus seeds
and a secondary consumer when it
eats ants or grasshoppers.
o The hawk is a secondary, tertiary, or
quaternary consumer, depending on
its prey.
 For humans to get the most calories per gram
of biomass eaten, they should eat…?... Meat?
Eggs? Grain?
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37.10 Describe the two components of
species diversity. Explain why large fields of
a single crop are vulnerable to devastating
disease.
Species diversity:
species richness: number of different species in a
community +
relative abundance, the proportional
representation of a species in a community.
Example: fig.37.10a,b
richness = 4 species
abundance = % of each species
Pathogens (viruses, bacteria, fungus)
infect a limited range of host species
(maybe just one). The more closely
spaced the hosts, the more likely the
pathogen will spread. (Irish potato
famine 1845 due to potato blight a
fungus).
37.11 Define a keystone species. Explain why
the long-spined sea urchin is considered a
keystone species.
A keystone species is a species whose impact
on its community is much larger than its biomass
or abundance indicate. It occupies a niche that
holds the rest of its community in place.
Researchers compare the species diversity with
and without the potential keystone species.
The long-spined sea urchin, Diadema, naturally
grazes on seaweed and scrape patches of
substrate clear of algae, providing platforms for
coral larvae to settle.
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In 1983, a disease killed massive numbers of
urchins.

Seaweed grew replacing the low turf of
encrusted red algae that is vital to reef building.

This prevented light from reaching symbiotic
dinoflagellates that corals depend upon for food.

In the following decade, the area of reef covered
by living coral animals plummeted, along with
overall species diversity.
37.12 Explain how disturbances can benefit
communities. Distinguish between
primary and secondary succession.
Communities are constantly changing due to
disturbances.
Disturbances are events such as:
 storms
 fire
 floods
 droughts
 overgrazing
 human activities can:
o damage biological communities
o remove organisms from them
o alter the availability of resources.
Disturbances can have a positive impact on a
community:
 tree falls in a storm creates new habitats
 More light can reach floor allowing new
plants to grow
 depression made by roots may fill with water
and used as egg-laying site for amphibians or
insects.
 Small disturbances increase patchiness which
increases diversity.
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Ecological Succession: Primary and
Secondary
Primary succession begins in a lifeless area with
no soil
o volcanic islands
o volcanic ash
o rubble from receding glacier
PRIMARY SUCCESSION
bare rock

autotrophic bacteria

lichens and mosses grow
from windblown spores

soil develops
from weathered rock and detritus

grasses and shrubs move in
windblown seeds or carried by animals

plants
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SECONDARY SUCCESSION
soil remains after a disturbance wipes out an
existing community. Example: clear-cutting
woods for a field then abandoning it as nutrients
are depleted.
SECONDARY SUCCESSION
Abandoned farm field becomes a hardwood
forest
(fig. 37.12)
Abandoned farm field

favorable to r-selected species
(early reprod. age, many offspring, no parental
care, competition not a major factor)

weedy annuals like crabgrass and ragweed

perennial grasses, small broadleaf plants

softwood species like pine after 5 years

pine forest in 10-15 years

hardwoods like oak and hickory take over
deciduous seedlings are shade tolerant, pine is
not.
Favorable to K-selected species.

final mixture of species depends on abiotic
factors
such as soil and topography.
animal community undergoes succession along
with plants
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37.13 Explain how invasive species can affect
communities.
An invasive species is a non-native species that
has been moved by humans either intentionally
and unintentionally. They can spread far beyond
original point of introd. and cause environmental
or economic damage by colonizing and
dominating wherever they find a suitable
habitat.
Example fig. 3713b:
 1859, 12 pairs of rabbits released on a ranch
in S. Australia by a European who wanted to
hunt familiar game.
 In 1865, 20,000 rabbits were killed on the
ranch
 By 1900, several hundred million rabbits
were all over the continent.
Catastrophic because:
 farm and grazing land became rabbit food
 loss of plant cover caused erosion
 Burrows made grazing treacherous for cattle
and sheep
 Competed with native herbivorous
marsupials
Biological Control: the intentional release of a
natural enemy to attack a pest population.
A virus lethal to rabbits was introduced
Several coevolutionary cycles followed
New viral strains introduced as rabbits became
resistant
1995, different pathogen used to maintain
control.
Article on eradication of European rabbit from
Australia.
http://www.sciencedirect.com/science
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ECOSYSTEM STRUCTURE AND DYNAMICS
An ecosystem consists of all the organisms in a
community as well as the abiotic environment
with which the organisms interact.
37.14 Compare the movement of energy and
chemicals through ecosystems. fig.
37.14
“Matter cycles, energy flows.”
37.15 Compare the primary production of
tropical rain forests, coral reefs, and
open ocean. Explain why the differences
between them exist.
Most of the energy of the sun is scattered,
absorbed, or reflected by the atmosphere or
surface of Earth. Of the visible light that reaches
plants, algae, and cyanobacteria (autotrophs),
only about 1% is converted to chemical energy
(glucose sugar) by photosynthesis.
Biomass is the amount, or mass, of living organic
material in an ecosystem.
The amount of solar energy converted to
chemical energy by an ecosystem’s producers for
a given area and during a given time period is
called primary production. (unit = g/m2/yr)
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Net primary productivity =
biomass produced – amt used by producers as fuel
for themselves
Highest:
algal beds and coral reefs
tropical rain forests
estuary
temperate deciduous forest
savanna
boreal forest (taiga)
cultivated land
temperate grassland
tundra
open ocean
desert and semidesert scrub

Lowest:
% of globe x productivity contributes to overall
production so open ocean contributes the most
overall because it is so vast.
37.16-17 Describe the movement of energy
through a food chain. Explain why there are
more producers than consumers and why
eating meat counts as a great luxury.
Energy supply limits the length of food chains.
fig. 37.16 Illustrates the cumulative loss of
energy with each transfer in a food chain. Only
10% of the energy available at each trophic level
becomes incorporated into the next higher level.
Only a tiny fraction of the energy stored by
photosynthesis flows through a food chain all the
way to a tertiary consumer. Top-level
consumers require a large geographic territory.
It takes a lot of vegetation to support trophic
levels so many steps removed from
photosynthetic production.
Food chains are limited to 3-5 levels; there is
simply not enough energy at the very top of an
ecological pyramid to support another trophic
level.
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Meat is a luxury for humans. fig. 37.17. Many
more people are supported by eating a
vegetarian diet. Feeding the vegetation to cattle
leaves much less to support humans.
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Explain how carbon, nitrogen, and
phosphorus cycle within ecosystems.
Chemical cycles in an ecosystem include both
biotic and abiotic (geological and atmospheric)
components; they are called biogeochemical
cycles.
Chemicals
Carbon
(Depends of
Photosyn. &
Cell Resp.)
fig.37.19
Phosphorus
(Depends on
weathering of
rock)
fig. 37.20
Nitrogen
(Depends on
bacteria)
fig. 37.21
Biotic Reservoir
Plants draw CO2 out of air into sugar
Passed along food chain by consumers
Cellular Resp. returns CO2 to atmosp.
Decomposers break down carbon compounds
in detritus and releases it as CO2
Burning wood and fossil fuels releases large
amts of CO2 back into the air.
Weathering of rock adds phosphate (PO4-3) to
the soil
Plants take up PO4-3 and make compounds
Consumers eat plants to get phosphorus
(PO4-3) returned to soil by decomposers
Runoff takes PO4-3 to the sea where it will
become incorporated into rock but not used
until geologic processes uplift rocks and
expose to weathering.
Nitrogen Fixation: (N2) + bacteria  nitrogen
compounds (NH4+) which can be used by
plants.
Mutualism between legumes and bacteria
Free-living bacteria both fix nitrogen.
(NH4+) in soil can convert to nitrate, (NO3-),
which is more readily absorbed by plants and
converted to protein.
Herbivores eat plants and also make protein.
Protein metab. releases nitrogen as urea (in
urine)
Decomposition releases (NH4+) to soil.
Abiotic Reservoir
Atmospheric
Fossil fuels
Dissolved carbon
compounds in
oceans
Sedimentary rocks
like CaCO3
Rocks
Atmosphere: 80%
N2 gas but is not
usable by plants.
Soil
Phosphates in fertilizers (commercial and animal
waste) can run-off into ponds. Phosphates are
scarce enough to be a limiting factor for algae.
Adding phosphates can cause an “algal bloom.”
So much algae grows that it does not produce
enough oxygen during the day to supply the
demands of cellular respiration throughout the
night. This can cause the pond, all the life in it, to
die. Also called eutrophication. fig. 37.23b
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