Components of benthic communities “Infauna” classified by size Bacteria & protozoa Macro- and meiofauna Major taxonomic groups Polychaetes, crustacea Echinoderms, molluscs In similar habitats, community composition suggests convergence in form
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?
Functional groups: examples of sediment stabilizers and bioturbators
More niches?, continued Biotic facilitation Mutualism Commensalism (e.g., inquilines in tubes)
Can disturbance facilitate diversity? Sources of disturbance Biotic disturbance Burrowing, sediment processing predation (exclosure experiments) Water turbulence, wave action Human disturbance Beam trawls – designed to scrape sediments a few centimeters below surface Otter trawls, etc. along surface Consider differences in scale
Effects of local and mid-scale disturbance Very patchy distributions Leading to high species turnover in space Lower density than required for competitive exclusion Superior competitor is reduced before inferior competitors disappear Recolonization patterns add to diversity because larval settlement depends on timing
Effects of trawling on bottom structure FishedUnfished Kaiser & Spencer. 1996. Journal of Ecology 65: 348-358