“螺-草”的互利关系

水生态系统中存在螺-草互利现象。然而，植食性螺类与水生植物之间是否存在这种互利关系目前尚无定论。椭圆萝卜螺（肺螺亚纲）与铜锈环棱螺（前腮亚纲）是常见的淡水螺类，其中，椭圆萝卜螺能牧食多种水生植物的活体。通过室外实验，研究了这两种螺类在不同密度条件下对沉水植物（苦草）生长的影响。实验结果表明，低密度的椭圆萝卜螺促进了苦草的生长，螺、草之间存在明显的互利关系，高密度时螺类对苦草植株本身的大量牧食则显著限制了植物的生长。对铜锈环棱螺而言，不同密度的螺类均明显促进了受附生生物胁迫的苦草的生长，螺-草互利关系成立。分析认为，螺-草互利关系的存在是有其限制条件的，对植食性螺类而言，只有在较低的螺类密度条件下才存在这种互利关系。

Mutualistic relationship between freshwater snails and aquatic macrophytes

Both pulmonate Radix swinhoei and prosobranch Bellamya aeruginosa are common freshwater snails in many Chinese lakes.Two outdoor experiments were conducted to investigate whether a mutualistic relationship exists between the two snail species and submerged plant Vallisneria spiralis.Results indicated that herbivorous snail R.swinhoei at low density stimulated V.spiralis growth through consuming and removing periphyton on plant leaves and the mutualistic relationship significantly existed between them,and as snail density were further increased,the evident herbivory of snails on live plant tissue suppressed the plant growth.For B.aeruginosa,the snails at experimental densities significantly stimulated plant V.spiralis growth,there is always a mutualistic relationship between them.This study suggests mutualistic relationships between freshwater snails and macrophytes depend on snail species.