Brenchley G A, Carlton J T
Biol Bull. 1983 Dec;165(3):543-558. doi: 10.2307/1541464.
During the nineteenth century the mud snail Ilyanassa obsoleta was abundant on sand and mud flats, wood works, sea walls, salt marshes, eel grass beds, and cobble beaches in New England. With the exception of sand and mud flats, these habitats are now largely occupied by the introduced periwinkle, Littorina littorea. To determine whether Littorina competitively displaces Ilyanassa, an experimental study was conducted at a site in Barnstable Harbor, Massachusetts where the observed distributions overlapped by 3% by Morisita's index. Mark-recapture studies suggested that the distribution of Littorina was limited by an abiotic factor, currents, through which this species realized its fundamental niche. In contrast, density manipulations demonstrated that Ilyanassa emigrated from areas where Littorina exceeded densities of 2 to 5 per 0.25 m. Littorina limited the upper and lower distribution of Ilyanassa and affected its microhabitat distribution in the mid intertidal zone. Habitat displacement was 70% for Ilyanassa, calculated as the difference between Ilyanassa's observed distribution and its distribution during littorinid removal experiments. The two species display reciprocal niche overlap with each possessing an exclusive region from which the other is physically restricted. The results suggest that the historical change in the distribution of Ilyanassa was due to competitive exclusion by introduced Littorina.
在19世纪，泥螺Ilyanassa obsoleta在新英格兰的沙滩和泥滩、木制品、海堤、盐沼、鳗草床和卵石滩上数量众多。除了沙滩和泥滩外，这些栖息地现在大多被引入的滨螺Littorina littorea占据。为了确定滨螺是否通过竞争取代了泥螺，在马萨诸塞州巴恩斯特布尔港的一个地点进行了一项实验研究，根据森下指数，观察到的两种螺的分布重叠率为3%。标记重捕研究表明，滨螺的分布受到非生物因素——水流的限制，通过水流该物种实现了其基础生态位。相比之下，密度操纵实验表明，泥螺会从滨螺密度超过每0.25平方米2至5只的区域迁出。滨螺限制了泥螺的上下分布，并影响了其在潮间带中部的微生境分布。泥螺的栖息地替代率为70%，计算方法是泥螺的观察分布与其在滨螺移除实验中的分布之间的差异。这两个物种表现出相互的生态位重叠，每个物种都有一个对方在物理上受到限制的专属区域。结果表明，泥螺分布的历史变化是由于引入的滨螺的竞争排斥所致。
