Testing redundancy at the source: Functional equivalence within a morphologically conservative genus of predators.
Resetarits, William*,1, Chalcraft, David2, 1 Old Dominion University, Norfolk, Virginia2 East Carolina University, Greenville, North Carolina
ABSTRACT- The idea that sets of species may have similar effects on population, community or ecosystem processes is a prevalent theme in many areas of ecology. If indeed species are functionally equivalent, limiting similarity suggests it should be closely related, morphologically similar species that use similar resources in a similar manner. We compared functional effects of three congeneric, morphologically similar fish species in the genus Enneacanthus, feeding on an ensemble of larval anuran prey consisting of Rana sphenocephala, Bufo terrestris and Hyla squirella. Individual predators were matched by body size within blocks to control for size effects. Response variables included both species specific (growth and survival of three species of larval anurans) and ecosystem level (total number and biomass of larval anurans) variables. Although two species (E. chaetodon and E. gloriosus) showed general similarity, the third (E. obesus) was significantly different in its effects on a variety of response variables; thus, only one of three possible species pairs could be judged functionally equivalent. The overall range of effects produced was surprising, given the similarity in morphology and autecology, strong phylogenetic affinity, and the fact that neither predator size nor growth explained significant variation. Our work suggests that functional equivalence may be uncommon, difficult to predict a priori, and that functional diversity, not functional equivalence, may underlie observed diversity-ecosystem function relationships.
Key words: community structure, species diversity , functional redundancy, ecosystem function
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