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 speciesOf 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. ricordii

A. insolitus usually percheson shady branches.

A. distichus perches on fenceposts and other sunny surfaces.

A. alinigerA. distichus

A. insolitus

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

Lake trout4.83 ppm

Con

cen

trati

on

of

PC

Bs

Herringgull eggs124 ppm

Smelt1.04 ppm

Phytoplankton0.025 ppm

Zooplankton0.123 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.