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. christophei A. distichus 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 Concentration of PCBs 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.