Download - Components of benthic communities
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Components of benthic communities “Infauna” classified by size
Bacteria & protozoaMacro- and meiofauna
Major taxonomic groupsPolychaetes, crustaceaEchinoderms, molluscs
In similar habitats, community composition suggests convergence in form
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Major questions What are the major components of
communities in unvegetated sediments? What is the relationship between
taxonomic classification and ecological function? (“Functional equivalents”)
How can disturbance promote diversity? What are the consequences of bottom-
dredging fishing techniques?
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Functional groups: examples of sediment stabilizers and bioturbators
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Parallel infaunal communities in North Temperate oceans: Ecological convergence
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Apparent paradox: high diversity, low habitat heterogeneity “Competitive” exclusion is observed Deposit feeders exclude suspension feeders
(really “amensalism”) Competition for space is documented
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Why not have more competitive exclusion? More niches than we thought?
Vertical sorting hypothesis
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More niches?, continued Biotic facilitation
Mutualism
Commensalism (e.g., inquilines in tubes)
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Can disturbance facilitate diversity? Sources of disturbance Biotic disturbance
Burrowing, sediment processingpredation (exclosure experiments)
Water turbulence, wave action Human disturbance
Beam trawls – designed to scrape sediments a few centimeters below surface
Otter trawls, etc. along surfaceConsider differences in scale
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Effects of local and mid-scale disturbance Very patchy distributions
Leading to high species turnover in space Lower density than required for
competitive exclusionSuperior competitor is reduced before
inferior competitors disappearRecolonization patterns add to diversity
because larval settlement depends on timing
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Effects of trawling on bottom structure
Fished UnfishedKaiser & Spencer. 1996. Journal of Ecology 65: 348-358
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Changes in community diversity with trawling
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Why does disturbance from trawling reduce diversity?
Direct effects on habitat
Scale of disturbanceDisrupt biotic interactionsReduce potential for recolonization
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Benthic processes: deep ocean systems
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Benthic processes: coastal, subtidal systems
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Benthic processes: vegetated, subtidal systems