COMPETITIVE DISPLACEMENT OF NATIVE MUD SNAILS BY INTRODUCED PERIWINKLES IN THE NEW ENGLAND INTERTIDAL ZONE.

摘要: During the nineteenth century mud snail Ilyanassa obsoleta was abundant on sand and flats, wood works, sea walls, salt marshes, eel grass beds, cobble beaches in New England. With exception of these habitats are now largely occupied by introduced periwinkle, Littorina littorea. To determine whether competitively displaces Ilyanassa, an experimental study conducted at a site Barnstable Harbor, Massachusetts where observed distributions overlapped 3% Morisita's index. Mark-recapture studies suggested that distribution limited abiotic factor, currents, through which this species realized its fundamental niche. In contrast, density manipulations demonstrated emigrated from areas exceeded densities 2 to 5 per 0.25 m2. upper lower affected microhabitat mid intertidal zone. Habitat displacement 70% for calculated as difference between Ilyanassa's during littorinid removal experiments. The two display reciprocal niche overlap with each possessing exclusive region other is physically restricted. results suggest historical change due competitive exclusion Littorina.