get from arehzo robert paine rocky temperate

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Unformatted text preview: es, mussels??? GET FROM AREHZO Robert Paine rocky temperate intertidal coastline in Washington macro invertebrate chitons, snails Predators increase diversity of species in an area 11/28/07 Why are there so many species in the tropics relative to temperate conditions? Disturbance – (perturbation) A relatively discrete event in time coming from the outside that disrupts ecosystems, communities, or populations, changes substrates and resource availability, and creates opportunities for new individuals to become established Examples: Wind, flood, fire, drought, animal overuse, and human activities (geese, deforestation by humans) Farming, mining, timbering, stream control, pollution, war, … Distubance Characteristics Size Frequency - # event per unit time Turnover – time between disturbances (ex: once every 5 years) Intensity – physical force of the event (saffer-simpson huricane scale) Severity – impact on the biota J.H. Connells Intermediate Disturbance Hypothesis: Moderate levels of disturbance increase species diversity Figure 16.18 Joseph Connell – INTERMEDIATE DISTURBANCE HYPOTHESIS High level of disturbance biodiversity is low (knocks populations back) Low levels of disturbances create competitive exclusion Medium levels of disturbances have the highest levels of species diversity *when a tree falls in the forest the resulting gap created increases diversity* At intermediate levels of disturbance there is a sufficient time to allow a wide variety of species to colonize but not enough time to allow competitive exclusion -happens in both terrestrial and aquatic enivornments A. Colonizing happens at high/frequent levels of disturbances – open up areas for new species to colonize B. Mixed medium diversity – balanced; not as many disturbances so many thrive C. Climax in low levels of diversity – Figure 16.19 Disturbance and diversity Wayne Sosa: Studied Algae in intertidal zone on boulders Looked at levels of disturbance and looked at the affect on the algae Looked at large rocks that less disturbed, small rocks easily moved found that they were only dominated by one colonizing species The largest rocks that moved the least with least disturbances had a decreased number of species b/c At intermediate levels of disturbance had highest levels of diversity (4-7 species) Figure 16.21 Support for Connell’s hypothesis in Terrestrial communities with prairie dogs Ex: Prarie dogs maintain a high level of disturbances by burrowing and creating dirt mounds. Continues the high diversity of grasses in the plains. Burrowing and grazing by prairie dogs increases the number of kinds of grass species within their praires DISTURBANCE GENERALIZATIONS Disturbance affects community equilibrium and, therefore, species diversity Disturbance is harmful to the individual and may be detrimental to the population or species, but often it is beneficial from the standpoint of maintaining or enhancing species diversity Disturbance and diversity Two quick points o Trophic dynamics Webs Energy flow o Production Primary Secondary Facilitation – enhanced growth, fitness, surv...
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This document was uploaded on 02/23/2014 for the course CHEM 107 at VCU.

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