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Community Ecology
 Diana Capalbo,
 Jane Joseph,
 Nicole Rebusi
 Sunny Yoo
“These sprays, dusts, and aerosols are now
applied almost universally to farms, gardens,
forests, and homes-nonselective chemicals that
have the power to kill every insect, the 'good' and
the 'bad,' to still the song of birds and the leaping
of fish in the streams, to coat the leaves with a
deadly film, and to linger on in soil-all this though
the intended target may be only a few weeds or
insects. Can anyone believe it is possible to lay
down such a barrage of poisons on the surface of
the earth without making it unfit for all life? They
should not be called 'insecticides,' but 'biocides.”
---Rachel Carson, Silent Spring
Biodiversity in an Ecological
Biodiversity is the range of organisms present in a particular ecological
community or system.
Chapter 53 discusses the biogeographic features that affect community
biodiversity. These factors include:
 Geographic size on the community: Species richness is directly related to
geographic size, and this is shown in the “Species-Area Curve”
 Equatorial Polar Gradients: Species richness generally declines along an
equatorial polar gradient.
Silent Spring describe many human activities that affect biodiversity. These
- Environment Destruction: Destruction of habitats all over the world is
happening so that agriculture, and urban development can take place.
-Introduced Species: Humans move species to new places, which can cause
rapid growth in population of the species in the new area, and cause more
competition in an are
-Biological Magnification: Since species become immune to certain pesticides or
insecticides, causing them to adapt and grow stronger; thus affecting the
community they live in.
A community is an assemblage of
populations of various species living
close enough for potential interactions.
Ex: trees and shrubs in Shenandoah
national park.
Interspecific interactions key relationships
in the life of an organ is in its interactions
with other species in the community.
They include: competition, predation, herbivory,
parasitism, mutualism, commensalism and
Interspecific competition is more likely to
occur in our world today because so many
resources are limited because of insecticides
and harmful toxics.
The animals that ate the plants quickly died
which led second consumers to interspecific
Also chemicals pass through water which
lead to a short supply of clean water which
leads to interspecific competition.
More then 200 basic chemicals have been
made to kill “pests” which lead carnivores to
a limited supply of meat which also lead to
interspecific competition.
Biological niche- organism’s job in the
community since harmful chemicals were
released to many types of organisms including
bees, the balance of nature has been thrown out
of control. The bee’s niche is to pollinate flowers
but if the flowers were harmful to the bees then
the bees will not be able to pollinate the flowers
which lead to no fruition which leads to a
decreased amount of food which leads to
competition and competitive exclusion principle.
Strontium used in nuclear explosions was
planted in the soil which contaminated plants
which caused interspecific competition.
Food Webs
In her novel, Silent Spring, Rachel Carson suggests ways
in which DDT and other pesticides/insecticides are
spreading to different species often causing death and
illnesses amongst these species.
Food webs are a series of food chains linked together
which are used by ecologists to summarize the trophic
relationships of a community (the feeding relationships
between organisms).
“And No Birds Sing”
According to the novel, food
webs play an important role of
the spread of DDT and other
pesticides/insecticides proven
by real-life events.
In 1954, Dr. Wallace and Mr.
Mehner at Michigan State
University researched robin
populations during the
spraying for the Dutch elm
disease on campus.
However, when the robins
migrated back the following
spring they were found dead
and dying all over the campus
because of insecticidal
“And No Birds Sing”
Dr. Roy Barker of the Illinois
Natural History Survey at Urbana
traced that the robins’ fate were in
the hands of the food web with the
elm tree as its primary producer.
The DDT sprayed on the trees sent
a streaming poison to all parts of
the trees while forming a
poisonous film over the leaves and
When the leaves fall to the ground,
they become one with the soil
which in turn is fed on by the
earthworms; elm being one of its
favorite foods. Thus, swallowing
the insecticide into their bodies
becoming “biological magnifiers” of
“And No Birds Sing”
One of the robins’ main
foods are earthworms.
Therefore, after the
robin has consumed
enough earthworms
with DDT it was most
likely to die resulting in
the end of the food
Poison Through The Web
This example is one of many
that have occurred during the
naïve usage of DDT and
other pesticides/insecticides.
The spraying of this poison
has contaminated plant life,
the primary producers, which
are consumed by animals and
humans therefore creating a
great “epidemic” throughout
the trophic structure (feeding
relationships) of life causing
death and illnesses which
could lead to extinction.
Humans have the greatest impact on
biological communities.
A disturbance is an event, such as a storm,
fire, flood, drought, overgrazing, or human
activity, that changes a community, removes
organisms from it, and alters resource
Effect on insects:
Some are killed by the
DDT & other
insecticides, while
others adapt and
become immune,
causing stronger, more
harmful formulas to be
Runoff from the toxic
soil caused rivers and
other bodies of water
Effect on
died or
birds: Many
became ill
worms, and
DDT is
Effect on fish: Many
species of fish died and
became ill.
example many trout
caused by DDT.
Effect on humans:
becomes toxic and
causes sickness.
Predation- herbivory- since DDT is fat
soluble it will build up as it moves in the food
chain. The storage of DDT begins with the
smallest conceivable intake of chemical and
continues until quite high levels are reached.
The fat storage depots act as biological
magnifiers, so that an intake of a little as 1/10
of 1 part per million in the diet results in
storage depots about 10 to 15 parts per
million, an increase of one hundredfold or
Diseases now are multiple-created radiation
in all its forms. As we contaminate soil, water,
and food we also poison the organism that
uses them to survive and then eventually
humans will be poisoned.
Chemicals Affect the WHOLE
Ecological Community
“In less than two decades of their use, the synthetic pesticides have been so thoroughly
distributed through the animate and inanimate world that that they occur virtually everywhere.
Residues of these chemicals linger in soil to which they may have been applied a dozen years
before. They have entered and lodged in the bodies of fish, birds, reptiles, and domestic and
wild animals…They have been found in fish in remote lakes, in earthworms burrowing in soil, in
the eggs of birds – and in man himself” (pgs 15 and 16)
“The problem of water pollution by pesticides can be understood only in context , as a part of
the whole system to which it belongs…” (pg39) “Water must also be thought of in terms of the
chains of life it supports- from the small as green cells of the drifting plant plankton, through the
minute water fleas to the fishes that strain plankton from the water and are in turn eater by
other fishes or by birds, mink raccoon –in a n endless cyclic transfer of materials from life to life”
(pg 46)
The world may find that insects and
rodents are pests but in reality, “pests” are
part of our community and they contribute
a niche and balance to all other life forms.
So instead of trying to eliminate organisms
we do not like, we should appreciate all
living things because our lives are not able
to exist without theirs.