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Lecture 9

BIOB50Winter2012 Lecture 9 and 10.docx - notes from lecture and text (includes images)

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Biological Sciences
Marc Cadotte

Lecture 9 and 10 Chapter 11CompetitionAG Tansley did one of the firt experiments on competition in 1917He wanted to explain the distribution of two species of bedstraw GALIUM HERCYNICUM which was restricted to acidic soils and G PUMILUM restricted to calcareous soils Tansley found that if grown alone each species could survive on both acidic and calcaereous soilsBut when grown together soil type determined which would surviveTansley inferred that competition restricted the two species to particular soil types in nature Organisms compete for resources such as food water light and spaceCOMPETITION CAN LIMIT THE DISTRIBUTIONS AND ABUNDANCES OF COMPETING SPECIESAs far back as Darwin competition between species has been seen as an influence on evolution and species distributionsINTERSPECIFIC COMPETITION is an interaction between two species in which each is harmed when they both use the same limiting resourceINTRASPECIFIC competition can occur between individuals of a single species Competition for ResourcesCOMPETITION occurs between organisms that share the use of a resource that limits the growth survival or reproduction of each species Examples of resources that be consumed to depletion include FOOD WATER IN TERRESTRIAL HABITATS LIGHT FOR PLANTS SPACE ESPECIALLY FOR SESSILE ORGANISMS AND SPACE FOR REFUGE AND NESTING MOBILE ANIMALSAn example of competition for space is corals and sea plants on rocks in the ocean Competing organisms reduce the availability of resourcesExperiments using two species of diatoms single celled algae that make cell walls of silica SiO2 were done by tilman et al 1981When each species was grown alone they reached a carrying capacity and silica concentrations were reducedWhen grown together the two species competed for silica and one species drove the other to extinctionWhen grown alone synedra and asterionella purple and red linesrespectively each reached a stable population size and reduced silica concentrations at low levels Synedra reduced silica concentration levels to lower levels than did asterionella and may explain why synedra outcompeted asterionella when the two species were grown together graph below When the two were grown together in competition synedra drove asterionella to extinction
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