Functional redundancy of stream detritivores : an experimental test
Date
2002
Authors
Shama, Lisa Nadine Saba
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Abstract
Relationships between species richness and ecosystem function may depend on the degree of functional differentiation vs. redundancy among coexisting species. Functional redundancy occurs when ecosystem function is maintained at nearly constant levels despite shifts in the populations driving that process. Detritivorous aquatic insect communities were experimentally manipulated by separately removing each of two dominant limnephilid caddisfly species to determine: (1) if species were functionally redundant, (2) if coexisting species interacted via inhibition or facilitation, and (3) if there were differential effects of intra- vs. interspecific density compensation. Per capita and per unit biomass effects of two response variables, leaf consumption (resource capture) and secondary production (insect growth) were compared. Density compensation was generally effective at maintaining leaf consumption after species loss, suggesting functional redundancy of the two caddisfly species. The two species, however, were not redundant for secondary production. Psychoglypha prita had significantly higher secondary production (during the experiment) than Psychoglypha sp. A Treatments containing the two species in combination showed less leaf consumption and secondary production than predicted by ' null models' of no interaction, indicating inhibition (interspecific competition) between the two species. In monoculture, interference competition may have decreased individual growth. In summary, classifying these two species as redundant depends on the response variable considered.