COMPETITION
Arises when organisms try to make
use of the same resources.
Intraspecific competition

occurs when
individuals of the
same species
compete for a
limiting resource.
(e.g. food, light,
nutrients, space).
Interspecific Competition
occurs when 2 different species compete for
a resource in short supply
Competitive Exclusion


Strong competition can lead to competitive exclusion,
local elimination of a competing species
The competitive exclusion principle states that two
species competing for the same limiting resources
cannot coexist in the same place
G.F. Gause – Competitive Exclusion
Principle
G.F. Gause – In 1932 developed
the CEP after researching mixed
cultures of yeast and Paramecium.
He concluded that no 2 species
can occupy the same niche at the same
time. Over time, one species will be
more successful & outcompete the other.
Competitive Exclusion Principle
1961 J.H. Connell
University of California
Ecological Niches



The total of a species’ use of biotic and abiotic
resources is called the species’ ecological niche
An ecological niche can also be thought of as an
organism’s ecological role
Ecologically similar species can coexist in a community
if there are one or more significant differences in their
niches

As a result of competition, a species’ fundamental
niche may differ from its realized niche

Resource partitioning
is differentiation of
ecological niches,
enabling similar
species to coexist in a
community
Robert MacArthur (1930 - 1972)
Studied 5 species
Of warblers which appeared to
be competing for the same
resource. MacArthur’s research
determined that each species
actually spent most of its time
feeding in different parts of the
tree and ate different subsets
of insects in the tree.
Fig. 54-2
A. distichus perches on fence
posts and other sunny surfaces.
A. insolitus usually perches
on shady branches.
A. ricordii
A. insolitus
A. aliniger
A. distichus
A. christophei
A. cybotes
A. etheridgei
Toxins in the Environment




Humans release many toxic chemicals, including
synthetics previously unknown to nature
In some cases, harmful substances persist for long
periods in an ecosystem
One reason toxins are harmful is that they become
more concentrated in successive trophic levels
Biological magnification concentrates toxins at higher
trophic levels, where biomass is lower
PCBs and many pesticides such as DDT are subject to
biological magnification in ecosystems
In the 1960s Rachel Carson brought attention to the
biomagnification of DDT in birds in
her book Silent Spring
Fig. 55-20
Herring
gull eggs
124 ppm
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
Ozone Shield Depletion


Pertains to O3 in stratosphere
Chlorine atoms from CFCs destroy O3
ex. Freon
cleaning agents
foaming agents
egg carton insulation & padding
Ozone shield is critical for all
living things


UV radiation causes mutations leading to:
skin cancer
cataracts
impairment of immune system
Also affects crop & tree growth and will
kill off algae and krill.
History on ozone depletion






Problem identified in 1980’s
Esp. above Antarctic in the spring
Propellants were banned in aerosols
1995 – U.S. halted production of CFCs
Chlorine pollution began to decrease
2000 – longer lasting polar clouds contribute to
breakdown of O3 by chlorine
pollution.