Lecture_25_community structure_1 April 20110

Lecture_25_community structure_1 April 20110 - I. Factors...

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I. Factors that contribute to diversity Environmental complexity allows for coexistence of organisms with different niches , preventing competitive exclusion
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Sometimes heterogeneity is subtle
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Fig 16.12
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Paradox of the plankton
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Paradox of the plankton G. Evelyn Hutchinson (1961) asked how so many different phytoplankton species can coexist when it appeared that they had the same niche. http://earthobservatory.nasa.gov/Experiments/ICE/Channel_Islands/
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G. David Tilman studied the mechanisms of resource competition The species that can best deplete a resource in the environment wins in competition Jargon for this – the species with the lowest R* wins
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Asterionella formosa Cyclotella meneghiniana Tilman compared the resource requirements of many diatom species and found that Asterionella has a lower R* for P compared to Cyclotella. Cyclotella has a lower R* for Si compared to Asterionella. Best competitor for P Best competitor for P Best competitor for Si Best competitor for Si
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Flow rate (volumes per day) Nutrient ratio [SiO2]/[PO4] 1,000 97 10 5.6 1.0 Asterionella wins P-limited Cyclotella wins Si-limited Stable co-existence Tilman conducted many studies in chemostats and linked the ratio of available silica and phosphorus with the outcome of competition between two diatom species
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Flow rate (volumes per day) Nutrient ratio [SiO2]/[PO4] 1,000 97 10 5.6 1.0 Asterionella wins Cyclotella wins Stable co-existence Cyclotella limited by PO 4 Asterionella limited by SiO2
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Flow rate (volumes per day) Nutrient ratio [SiO2]/[PO4] 1,000 97 10 5.6 1.0 Asterionella wins Cyclotella wins Stable co-existence Intra -specific competition is greater than Inter -specific competition
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What happens when you reduce environmental complexity? Most clear tests result from nutrient enrichment studies – e.g. Rothamsted, England The Park Grass experiment – fertilizing grassland plots since the mid 1800s.
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I. Factors that contribute to diversity B. Disturbance Intermediate levels of disturbance promote higher diversity. Intermediate Disturbance Hypothesis (Connell 1975, 1978) WHY?
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Figure 16.18
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Whicker and Detling 1988
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WHY? Remember Grime’s classification of plant life history
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Lecture_25_community structure_1 April 20110 - I. Factors...

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