Larval predation by epifauna on temperate reefs: scale,power and the scarcity of measurable effects

Benthic suspension feeders often occur at high densities on temperate reefs and other hard bottoms. Beeause many such organisms hayc prodigious feeding rates in the laboratory, it has often been predicted that established epifauna would deplete larval populations, thereby influencing density, spatial distribution and species eomposition at settlement. Most field manipulations of filter-feeder density have not controlled for faetors other than larval predation that could produce the same pattern. In controlled experiments, larval predation effects are seldom observed. Intermittent feeding and small radii of predator influenee present many more opportunities for settlement than has generally been assumed. Two important faetors often foil attempts to measure predation effeets: low statistieal power due to small effect sizes, and choice of spatial scales larger than thdse where predation effeets oeeur.     

On the advantages of crossed mandibles: an experimental approach

The importance of the crossed mandibles to crossbills for foraging on conifer cones was studied by removing most of the crossed portion of the mandibles of two Red Crossbills L. curvirostra. The foraging rate of these two bill-altered crossbills on the cones of three species of conifers was compared to their rates prior to bill alteration and to two controls. The mandible crossing proved essential for extracting seeds from closed cones. However, as cones open the bill crossing becomes less critical. The mandible crossing appears to be one of several adaptations of crossbills that have extended the period during which conifer seeds can be exploited effectively.